PROJECT NUMBER: PNA010-0708

MARKET ACCESS & DEVELOPMENT

JULY 2009

Advanced research into floor performance issues Sub project: Concrete slab moisture and associated ongoing timber performance

This report can also be viewed on the FWPA website

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Advanced research into floor performance issues Sub project – Concrete slab moisture and associated ongoing timber performance

Prepared for

Forest & Wood Products Australia

By

P. Beale, R. Diggins and G. Dzinotyiweyi

Publication: Advanced research into floor performance issues Sub project – Concrete slab moisture and associated ongoing timber performance Project No: PNA010-0708 © 2009 Forest & Wood Products Australia Limited. All rights reserved. Forest & Wood Products Australia Limited (FWPA) makes no warranties or assurances with respect to this publication including merchantability, fitness for purpose or otherwise. FWPA and all persons associated with it exclude all liability (including liability for negligence) in relation to any opinion, advice or information contained in this publication or for any consequences arising from the use of such opinion, advice or information. This work is copyright and protected under the Copyright Act 1968 (Cth). All material except the FWPA logo may be reproduced in whole or in part, provided that it is not sold or used for commercial benefit and its source (Forest & Wood Products Australia Limited) is acknowledged. Reproduction or copying for other purposes, which is strictly reserved only for the owner or licensee of copyright under the Copyright Act, is prohibited without the prior written consent of Forest & Wood Products Australia Limited. ISBN: 978-1-920883-73-7 Researcher: P. Beale, R. Diggins and G. Dzinotyiweyi The University of Western Australia 35 Stirling Highway CRAWLEY, WA, 6009 Final report received by FWPA in July, 2009

Forest & Wood Products Australia Limited Level 4, 10-16 Queen St, Melbourne, Victoria, 3000 T +61 3 9614 7544 F +61 3 9614 6822 E info@fwpa.com.au W www.fwpa.com.au

Contents

1.0 Introduction ...................................................................................................................... 1

1.1 Aim of Report ................................................................................................. 1

1.2 Testing Methods used .................................................................................... 1

1.3 Breadth of Research ....................................................................................... 1

2.0 Testing Conditions ........................................................................................................... 2

2.1 Overview of Climatic Conditions and Soils ...................................................... 2

2.2 Slab Construction ............................................................................................. 4

2.3 Admixtures ........................................................................................................ 5

3.0 Assessing Moisture Measuring Techniques ................................................................... 7

3.1 Findings from Literature on Testing Methods .................................................... 7

3.2 Tests and Results .............................................................................................. 8

3.21 Overview of Calcium Chloride Test (MVER) ......................................... 8

3.22 Overview of Relative Humidity Sleeve Test ......................................... 13

3.23 Overview of Insulated Relative Humidity Testing Box .......................... 15

3.24 Overview of Rapid Relative Humidity (RH) Probes .............................. 17

3.25 Overview of Electrical Resistance Probes ........................................... 18

3.26 Overview of Capacitance Meter Test ................................................... 20

3.3 Test Summary and Recommendations ............................................................. 22 4.0 What Deems the Slab Ready to Accept Timber Flooring? ............................................ 24 5.0 Influencing Factors on Flooring Behavior Other Than Concrete Moisture Content .................................................................................................................................................... 26

5.1 Case Study Title: Cupping Floor in High Wycombe, Perth, Western Australia......................................................................................................................... 26 5.2 Case Study Title: Cupping Floor in Hillarys, Perth, WA ...................................... 27

5.3 Air-conditioning ................................................................................................... 27

5.4 Ambient Environmental Conditions .................................................................... 28

6.0 Timber Flooring ................................................................................................................. 29 7.0 Concluding Recommendations ....................................................................................... 31 8.0 References ......................................................................................................................... 38

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Executive Summary Objective: The objective of this research was to evaluate commonly available methods for determining the moisture content in concrete slabs. Through the processes of testing and evaluation the Advanced Timber Concepts Research Centre (ATC) was to provide a reasonable estimate of the length of time it takes a concrete slab to dry so that timber flooring could be laid directly on the slab without chance of failing thereafter. Quantitative Tests conducted by the ATC comprised of:

- Calcium Chloride Test (MVER) -Relative Humidity Sleeve Test - GE Protimeter depth-selectable humidity sleeves - Electrical Resistance Probe Test -Bollman BES Combo 100 resistance meter - Insulated Relative Humidity Testing Box -Rapid Relative Humidity Probe - Tramex “Concrete Encounter” Capacitance Meter

Key Findings: Over the Period of 18 months, the ATC conducted multiple tests on a total of 29 sites, nine in the North-West of Western Australia, seven in the South-West, three in Kalgoorlie, and 10 in the Perth metropolitan region. These sites encompassed four of the five different climatic zones of Western Australia and all tests were conducted on job sites awaiting application of direct stick timber flooring. The key findings were as follows:

- The time it takes a slab to dry varies between slabs and will be influenced by the climatic zone the slab is in, the cement mix used and if any chemical admixtures have been employed in the mix.

- MVER and Relative Humidity Box tests are influenced substantially by ambient climatic conditions. Warmer, more humid air can yield a higher MVER even if the internal concrete moisture condition is unchanged.

- There is no strong correlation between MVER and Relative Humidity test results and no constant by which to measure MVER results.

- Methods of determining moisture content in concrete slabs may be influenced by the chemical make-up of the original concrete mix. Electrical Resistance Probe tests conducted by the ATC were all influenced by chemical admixtures outside of the Perth Metropolitan region. Calcium chloride tests show deceptively low results where set-retarding mixtures have been used and deceptively high results where accelerating mixtures are used. Where chemical admixtures have been employed, the MVER, electrical capacitance and resistance tests can be used as qualitative rather than quantitative test methods.

- The test results differed between slab-on-ground and suspended slabs. The internal temperature of a slab-on-ground is affected by the sub-slab soil temperature, whereas the internal temperature of a suspended slab is driven by the temperature of the air-space above and below.

- Relative Humidity Sleeves consistently returned the most reliable results and did not appear to be influenced by chemical admixtures or external climatic conditions.

- The age of a concrete slab effects and changes the ability of it to transport water. An older, re-wetted slab will take a substantially longer time to dry than a newly poured slab.

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Interpretation of Results:

- Various testing methods should be employed over the slab to gauge the overall behavior of moisture at a time when the building can accurately reflect in-service conditions.

- The ATC suggests that a slab should be tested for suitability after the three-month period stipulated as the length of time it takes a concrete slab to dry by the Cement Concrete & Aggregates Association. If the slab is deemed suitable for timber flooring after this time, it may still be good practice to install a moisture barrier between the concrete and timber flooring. Any timber flooring failure after this point is more likely to be attributed to fluctuation of the internal relative humidity of the building when in-service, or that the timber was not stored / acclimatised properly or was prone to failure.

 

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1.0 Introduction 1.1 Aim of Report The aim of this report was for the Advanced Timber Concepts Research Centre (ATC) to evaluate commonly available methods of determining the moisture content in concrete slabs. Through the processes of testing and evaluation it was expected that the ATC could provide a reasonable estimate of the length of time it takes a concrete slab to dry so that timber flooring could be laid without chance of failing thereafter. The following report outlines the reasons why such a figure is idealistic, and not appropriate, and pays particular attention to concrete behavior within the different climatic regions of Western Australia. It also provides a matrix demonstrating which testing methods give the most accurate results under different conditions. 1.2 Testing Methods used There are both qualitative and quantitative methods of testing for concrete moisture content. Qualitative methods, which involve covering the concrete surface with an impermeable material such as a rubber mat, glass or a plastic sheet, will indicate whether moisture is moving through the slab. Quantitative methods will provide the fundamental connection between qualitative observation and mathematical expression of quantitative relationships. After reviewing literature on the commonly available tests for moisture testing of concrete, the ATC decided to conduct the following quantitative tests:

• Calcium Chloride Test (MVER) • Relative Humidity Sleeve Test - GE Protimeter depth-selectable humidity sleeves • Electrical Resistance Probe Test - Bollman BES Combo 100 resistance meter • Insulated Relative Humidity Testing Box • Rapid Relative Humidity Probe • Tramex “Concrete Encounter” Capacitance Meter

1.3 Breadth of Research Over the research period of 18 months the ATC conducted tests on a total of 29 sites, nine in the North-West of Western Australia, seven in the South-West, three in Kalgoorlie, and 10 in the Perth metropolitan region. All of these sites were visited at least twice. All of the case-study sites have been tested by a combination of tests mentioned in Section 1.2. The ATC tested slabs which varied in age, and had three sites in Perth and two in Kalgoorlie which were considered mature slabs. It should be noted that the new slabs tested were exposed to the weather on the first visits, and on some of the subsequent return visits. This obviously rendered these tests void, and was taken into consideration when assessing the accuracy and the reliability of the individual testing methods.

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2.0 Testing Conditions 2.1 Overview of Climatic Conditions and Soils Information on climate was sourced in form of extracts from the Australian Bureau of Meteorology. Information on soils came from the Atlas of Australian Soils.1 Western Australia covers an area of some 2.5 million square kilometres and extends over a latitude band from about 14 degrees south to 35 degrees south. Consequently there are a variety of climatic zones, ranging from the north Kimberley, where heavy rains are experienced in the summer 'wet' season, through the mostly dry interior which endures excessive summer heat, to the South-West’s distinctively Mediterranean climate.2 Our testing has taken place in Broome in the North-West, Kalgoorlie in the East, Manjimup, Busselton and Dunsborough in the South-West and within the suburban area of Perth. According to the Building Code of Australia’s 2007 Climatic Zone Map (Image 1), Broome is in Zone 1, Kalgoorlie is in Zone 4, Perth, Busselton and Dunsborough are in Zone 5, and Manjimup is in Zone 6. Broome The climate of Broome is tropical by nature and is characterised by hot and humid summers and warm winters. There are two distinct seasons: the ‘wet’ usually from December to March and the ‘dry’ for the remainder of the year. The median annual rainfall is 532 mm on an average 44 days, although there is considerable variation from year to year. Evaporation is high, and in November the average daily rate is 9.5 mm per day. The relative humidity is generally uniform from month to month, averaging about 60 - 70 % at 9 a.m., while at 3 p.m. values range from about 35 % in the cooler months to about 60 % in the wetter months.3 During the ATC’s second round of testing during February 2008, the afternoon relative humidity peaked at 94%. The soils of Broome are sandy with weak pedologic development. They are red sands with an earthy fabric. Kalgoorlie Kalgoorlie-Boulder has a dry climate with hot summers and cool winters. The average annual rainfall is 260 mm on an average of 65 days, and while the average rainfall is fairly evenly distributed throughout the year, there is considerable variation from year to year. January is the hottest month with an average maximum temperature of 33.6°C. By contrast winters are cool with July average maximum and minimum temperatures being 16.5°C and 4.8°C respectively. The majority of the annual average evaporation of 2664 mm occurs from November to February. The average rate in January is 12.7 mm per day, while on a hot windy day the evaporation can be over 20 mm. During the winter the average daily evaporation decreases to 2.6 mm. The relative humidity averages less than 30% at 3 p.m. during summer while the 9 a.m. winter figures are typically around 70%.

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The soils of Kalgoorlie are loamy with weak pedologic development, i.e. shallow calcareous soils. Perth Perth experiences a Mediterranean climate, characterised by hot dry summers and mild wet winters. These seasons extend into the autumn and spring months, which are transitional periods between the main seasons. Mean monthly air temperature range from 31°C in February to 18°C in July and August. Summer maximum temperatures are strongly dependent upon the arrival time of the reliable sea breezes. On some days the difference between the maximum temperatures on the coast and the eastern suburbs may exceed 10°C. Mean daily pan evaporation ranges from a maximum of about 10 mm in January to just 2 mm in June and July. The average annual evaporation exceeds 2000 mm. The majority of the Perth metropolitan area is sited on sandy soils. Water infiltration of the sands is rapid. South-West (Busselton, Dunsborough, Manjimup) The climate of the South-West is mainly temperate / Mediterranean and it does not differ greatly from that of Perth. With the latitudinal difference, temperatures tend to be lower than those of Perth and rainfall tends to be higher. Although Busselton, Dunsborough and Manjimup can be categorised under the same climatic region, their soil structures differ greatly. Busselton has calcareous sandy soils of minimal development, Dunsborough lies on grey leached earths, and Manjimup sits on hard-setting loamy soils with mottled yellow clayey sub-soils. Water infiltration is rapid and the available water store is small.

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Image 1: Building Code of Australia’s 2007 Climatic Zone Map 2.2 Slab Construction All slabs observed appear to have been constructed according to good building practices in Western Australia. The concrete that has been used is of no less than N20 grade and most floors are the 100 mm standard thickness. All edge rebates of the ground slabs have been flashed and drained according to AS2870 to prevent water ingress into the building and drainage has been designed and constructed to avoid ‘water ponding’ against or near the footings / slab in most cases. As the Australian Building Codes require, all newly constructed slabs have been laid with a vapour barrier. The tested slabs come from a range of different building types. These include buildings of solid masonry, steel frame brick veneer, steel frame with steel cladding, and Formcraft construction (an example of which is in Broome). Formcraft consists of insulated concrete formwork which uses high density expanded polystyrene panels as a form to accept steel reinforced concrete. This method of construction is becoming increasingly popular in Australia. All structures report protection of their ground slabs from the ingress of precipitation and other forms of moisture accordingly. Since we were aiming to test a slab’s response to seasonal ambient temperature and relative humidity change, it must be kept in mind that there will be considerable differences between the readings of slabs in the same climatic zoning, but at different stages of construction. For

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example, an open slab will be greatly affected by the atmospheric conditions of the locality, however, a slab which is at the ‘lock-up’ point of construction will be less so. The test results also differ between slab-on-ground and suspended slab. This is because concrete slabs in contact with the earth are a heat sink and their internal temperature is affected by both the sub-slab soil temperature and by the temperature of the air space above. However, the internal temperature of a suspended concrete slab will be driven by the temperature of the air space above and below the slab. There is a trend in some areas to apply slab moisture barriers before laying flooring. The recommendations concluding this report consider the necessity of such barriers. 2.3 Admixtures Why they are used Chemical admixtures are materials in the form of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. They are generally less than 5% of the mass of the cement. There are two common types of admixtures employed in Western Australia to deal with the extremes in climate. These are accelerating admixtures and set-retarding admixtures. Accelerating admixtures speed up the hydration of the concrete. The effective component of the admixture is inorganic salts, or calcium chloride. The admixture works to increase the rate of early strength development in the concrete, which reduces the time required for proper curing and protection and speeds up the start of finishing operations. Calcium chloride also lowers the free water content of the concrete faster. Accelerating admixtures are therefore presumed to be particularly useful for modifying the properties of concrete in cold weather; for example, the ATCs case study on Perup Road, Manjimup, used Hanson Concrete’s SuperSet Silver mix. The opposite is true for set-retarding admixtures. Retarders are known to delay the hydration of concrete, and are used to counteract the accelerating effect of hot weather on concrete setting, without affecting the long term mechanical properties of the concrete. High temperatures can cause an increased rate of hardening which makes placing and finishing difficult. Retarders keep concrete workable during placement and delay the initial set of concrete. Readymix with Daratard concrete mix was used on multiple case study slabs in Broome. Where they have been used Our research has shown that set-accelerating admixtures have been prevalent in the cooler climates of the South-West, and set-retarding admixtures have been employed in the warmer locality of Broome. The slabs we tested in Perth have not had any admixtures added while those in Kalgoorlie have had set-accelerating admixtures added as the slabs were poured in winter. In summer, however, the concrete suppliers in Kalgoorlie tend to add set-retarding admixtures to their concrete due to the intense heat and evaporation that can be experienced in that region.

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How Admixtures Effect Test Results The ATC hypothesised early in the project that test results from localities outside of Perth, where admixtures are more likely to be used, would vary in their accuracy. Our assumptions were:

• Calcium Chloride Tests are likely to show deceptively low moisture vapour emission rate results where set-retarding admixtures have been used, as the flow of free water in the slab is, to a degree, inhibited.

• Where accelerating admixtures have been used, the flow of free water from the slab is likely to be faster, and will result in a false high MVER.

• Admixtures are likely to interfere with the conductivity of concrete, and as a result, any readings obtained through the use of the Bollman resistance meter, or the Tramex Capacitance Meter, cannot be considered to be entirely reliable.

Results will be discussed further in this document.

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3.0 Assessing Moisture Measuring Techniques 3.1 Findings from Literature on Testing Methods The following table gives the upper moisture content limits for concrete recommended by each test when applying timber flooring (Table 1): Table 1: Available tests and recommended moisture levels before applying timber flooring. Test Upper moisture limit recommended for the

application of timber flooring Calcium Chloride Test 1360.7g / m² / 24 hr* Relative Humidity Sleeve Test 70% relative humidity Insulated Relative Humidity Box Test 70% relative humidity Rapid Relative Humidity Probe 70% relative humidity Capacitance Meter Test 5.5% moisture content Electrical Resistance Probe Test 5.5% moisture content

* In the article When 3lbs is not 3lbs 4, it is stipulated that properly conducted calcium chloride tests often result in values higher than the 3-lb (1360.7g) MVER required by most flooring manufacturers. This figure is the total moisture vapour evaporation over a 24 hour period and differs significantly from the 170 g / m² / second recommended on the Papworths Pty Ltd Calcium Chloride Moisture Test 3-Pack – Test Procedure sheet. It is assumed that the figure given by Papworths is incorrect. AS/NZS 2455 states that textile floor coverings shall not be laid until the moisture content is not more than 5.5% or the relative humidity level is not more than 70%. This is relevant to all tests other than the calcium chloride test. There is some ambiguity about these figures. Firstly, the 5.5% moisture content figure seems purely anecdotal. Research by the ATC did not uncover the origins of this figure. Some speculate that 5.5% is:

• A moisture level at which typical adhesives (for vinyl for example) are at risk • Related to average relative humidity (the moisture in concrete will not be less than the

ambient relative humidity) • A moisture level at which the applied products could be affected.5

If we are to question the consistency of 5.5% as a standard, then it only makes sense to question 70% as the upper limit for the internal relative humidity. Before moisture-sensitive floor coverings can be installed, Swedish specifications require the concrete’s internal relative humidity to reach 85%. As a relative humidity reading of 75% for a slab equates to a moisture content of about 2%6, it is alarming that the concrete could be almost fully saturated and still have moisture content less than 5.5%.7 Another anomaly is the anhydrous Calcium Chloride Test. This test for moisture emission rate (MVER) was developed in the 1940s as a qualitative evaluation of floor moisture condition. Without any scientific basis, it became a quantitative test in the 1960s8. It is now “widely used by the flooring industry”9. Howard Kanare, author of Concrete Floors and Moisture10, works with CTLGroup who have investigated the performance of the MVER test over the last decade, and have found “it suffers from several serious deficiencies”11. The most discouraging of these

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deficiencies is the interference of ambient conditions on test results. Kanare reports that “warmer, more humid room air can yield higher MVER results even if the internal concrete moisture condition is unchanged”12. The calcium chloride test is a measurement of dynamic volume whereas the other tests undertaken are a measure of static content. So far, there is no established relationship between the two measures. Many studies have been done to find that correlation, but it is not well defined13. Any MVER tests conducted by the ATC have been coupled with an RH test, an electrical resistance or capacitance test, or a combination of the three. Below is a table of lengths of time each test needs to be conducted to gain accurate results (Table 2): Table 2: Required testing times for concrete moisture levels Test Testing Period (hours)Calcium Chloride Test 60 - 72 Relative Humidity Sleeve Test 72* Insulated Relative Humidity Box Test 72 Rapid Relative Humidity Probe 0 (instantaneous) ^ Electrical Resistance Probe Test 0 (instantaneous) Capacitance Meter Test 0 (instantaneous)

* Sleeve should be in slab 72 hours prior to testing, to allow moisture to redistribute evenly after drilling of slab. ^ Test is instantaneous only after the device has been placed into the slab. 3.2 Tests and Results

3.21 Overview of Calcium Chloride Test (MVER) As mentioned in Section 3.1, the Calcium Chloride Test is a measure of the moisture vapour evaporation rate from the slab, and is not indicative of the moisture content of the concrete. The Calcium Chloride Test gives an estimate of the movement of the moisture within the upper portion of the slab. Application of flooring without testing beyond this initial 20 mm depth could ultimately lead to flooring failure. In such a scenario, if the concrete is covered by flooring with low permeability too early, the moisture content will continue to equalise within the thickness of the slab, and the moisture will have nowhere to flow. As the flooring becomes a barrier that inhibits the escape of excess moisture vapour that may have been present in the deeper portion of the slab before the flooring was applied, the build-up of moisture below the surface of the flooring will ultimately cause the flooring to fail. As the MVER test does not give the actual moisture content of the slab, it is recommended that this test is used in conjunction with either a relative humidity sleeve test or an electrical resistance test, to understand both the location and quantity of moisture within the slab. It is also necessary to undertake multiple MVER tests over the one slab. Positions which are exposed to direct sunlight will generally have a higher MVER then positions which are not. It is also true that upper storey slabs exposed to the air on both faces will dry at a different rate to those which are slab-on-ground. In order to obtain the optimum result from the Calcium Chloride Test, it is necessary for it to be carried out in an enclosed building space that reflects the anticipated in-service conditions at least 48 hours prior to the test being performed14. If this is not possible (for example, where the HVAC

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system has not yet been installed), then the test should be performed when the temperature is 23.9°C +/- 5.6 °C with the RH at 50% +/- 10%. As mentioned above, these tolerances are quite important as moisture within slabs will ‘flow’ according to ambient temperature and humidity changes. Chemical admixtures will affect the flow of moisture though the slab (results will either prove too low or high depending on the type of admixture). In such case the Calcium Chloride Test should be used as a qualitative test, rather then quantitative. It is also important that testing surfaces are free of contaminants such as residue from paint, adhesives or from parting compounds. The presence of these substances will restrict moisture release and test results will be too low. Influencing environmental factors Tables 3(a) and 3(b) have been constructed to demonstrate the influence of ambient temperature and relative humidity on the moisture vapour evaporation rate:

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Table 3(a): Results of MVER during first round of tests. Site Date of

Testing Age of Slab

Covered/ Exposed

Ambient Temp (°C)

Ambient Relative Humidity (%)

MVER (g/m²)

Lot 325 Banu Rd, Broome

19.10.07 21 days Exposed 29.6 59 663.99

362 Biny Lane, Broome

14.12.07 4 months Exposed 30.3 71 641.80

Jigill Rd, Broome

14.12.07 2.5 months

Exposed 30.3 71 727.15

Lot 1 Scott St, Broome

14.12.07 3.5 months

Exposed 30.3 71 Upper Floor: 397.71 Lower Floor: 479.64

Snowbill Rd, Broome

14.12.07 6 months Covered 30.3 71 371.25

17 Cathedral Loop, Busselton

30.11.07 5 months Covered 20.1 61 259.45

57 Glover Rd, Dunsborough

30.11.07 1 month Exposed 20.2 66 240.68

Perup Rd, Manjimup

02.12.07 1 month Exposed – rain during testing

20.7 56 Wardrobe: 1026.71 Bedroom 5: 891.86

Sherrington Rd, Manjimup

02.12.07 1 month Exposed 20.7 56 669.96

26 Thorpe St, Rockingham

29.11.07 2 months Exposed 21.8 52 468.55

8 Morgan St, Shenton Park

14.11.07 Old Slab: 33 years New Slab: 3 months

Exposed 22.6 48.5 Old Slab: 666.55* New Slab: 340.53

18 Lincon St, Vasse

30.11.07 12 months Covered 20.1 61 215.92

Note: Ambient temperature and ambient relative humidity are averaged over a 72 hour period. * Old slab had been exposed during the winter season.

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Table 3(b): Results of MVER during second round of tests Site Date of

Testing Age of Slab

Covered/ Exposed

Ambient Temp (°C)

Ambient Relative Humidity (%)

MVER (g/m²)

Lot 325 Banu Rd, Broome

06.02.08 5 months Covered 30.8 80 614.5

Lot 1 Scott St, Broome

06.02.08 5.5 months

Covered 30.8 80 Upper Floor: 473.7 Lower Floor: 896.1

Spoonbill Rd, Broome

06.02.08 8 months Covered 30.8 80 Upper Floor: 448.1 Lower Floor: 460.9

17 Cathedral Loop, Busselton

04.02.08 7 months Covered 25.6 51 546.2

57 Glover Rd, Dunsborough

04.02.08 3 months Exposed 25.6 51 614.5

Perup Rd, Manjimup

04.02.08 3 months Exposed 20.3 74 Wardrobe: 614.5 Bedroom 5: 597.4

Sherrington Rd, Manjimup

04.02.08 3 months Covered 20.3 74 435.3

In Table 3(a), most of the slabs tested were in their initial four months of construction and largely uncovered. Of all the sites shown in the table above, only 18 Lincon Street, Vasse, was fully enclosed. Snowbill Rd and 17 Cathedral Loop were about to have the glazing installed when the concrete testing was being carried out. A comparison of the tables above demonstrates that MVER tests are influenced by ambient atmospheric conditions. A MVER test on the slab in Banu Road, Broome returned a result of 664.0 g/m². This is not a realistic MVER for the slab under in-service conditions as the project was not yet at lock-up stage of construction, and the slab was still exposed to the weather. However, as the Bollmann electrical resistance test returned an in-slab moisture content of 2.6%, and the mean daily temperature during the month of testing (October) was 32.8°C, this scenario demonstrates that ambient conditions interfere with test results. That is, warmer, more humid air can yield higher MVER results even if the internal concrete moisture condition is unchanged. As mentioned earlier, the results of MVER testing on ground slabs and suspended slabs will differ due to the proportion of surface area exposed to ambient conditions. In terms of the MVER test, this would correlate to a higher MVER from a slab-on-ground, and a lower MVER from a suspended slab. This is demonstrated by a comparison of the MVER readings taken from a two storey residence in Broome. The suspended slab revealed a moisture vapour emission rate of 397.71 g/m², whereas the emission from the ground slab was 479.64 g/m² (Table 3(b)).

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Summary of Test There are many variables which can affect the Calcium Chloride Test, and no constant to compare results with. It is alarming that all of the MVER tests conducted by the ATC returned results appropriate to lay timber flooring even if the slab was still exposed to the weather (see Image 2). Although it is crucial to understand the movement of moisture within the slab, there are too many influencing factors and grey areas to make it a reliable test as it stands. It is recommended that this test is revised before its use is encouraged in Australia However, David Hayward, Technical Manager for the Australian Timber Flooring Association, suggests that from a floor installers’ point of view the Calcium Chloride Test is too difficult and installers will not use it15.

Image 2: “Most of the slabs tested were in their initial four months of construction and largely uncovered”. Obviously this test should have failed due to influence of ambient conditions. The MVER reported to be 1011.3 g/m2/24 hr however, which is within the 1360.7g/m²/24 hr upper limit for concrete moisture content when applying timber floors.

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Relative Humidity Tests Table 4(a): Results of relative humidity tests during first round of testing. Site Ambient

Temp (°C)

AmbientRH (%)

Slab Covered/ Exposed

Humidity Box Readings (%)

Humidity Sleeve Readings at 60mm depth (%)

Rapid Relative Humidity Readings (%)

Biny Lane, Broome

30.3 71 Exposed 87 81 84

Scott St, Broome

30.3 71 Exposed 82 80 83

Glover Rd, Dunsborough

20.2 66 Exposed 86.5 95.7 97

Perup Rd, Manjimup

20.7 56 Exposed* - 88.5 88

Morgan St, Shenton Park

22.6 48.5 Exposed 73.8 63.6 74

* Rained during testing period Table 4(b): Results of relative humidity tests during second round of testing. Site Ambient

Temp (°C)

AmbientRH (%)

Slab Covered/ Exposed

Humidity Box Readings (%)

Humidity Sleeve Readings at 60mm depth (%)

Rapid Relative Humidity Readings (%)

Banu Rd, Broome

30.1 89 Exposed 91.4* - -

Scott St, Broome

30.1 89 Exposed 93.4* 78.8 Not functioning

Cathedral Loop, Busselton

26 52 Covered 79 71.8 -

Glover Rd, Dunsborough

26 52 Exposed - 56.5 Not functioning

Perup Rd, Manjimup

21.2 74.5 Exposed* 92* 95.2 79

Sherrington Rd, Manjimup

21.2 74.5 Covered 80.9 69.5 Not functioning

* Rained during testing period 3.22 Overview of Relative Humidity Sleeve Test Relative Humidity (RH) testing gives a much more useful and accurate measurement of the actual moisture condition within the concrete. Unlike the Calcium Chloride Test, electrical resistance and (to a certain extent) capacitance tests, sleeve tests are not affected by concrete additives or aggregate types, or by ambient relative humidity and temperature. As with all tests, a number of RH sleeves should be inserted over the slab. It is good practice to make two readings in areas up to 25 m², three readings in areas up to 100 m², and six readings in areas up to 500 m². Sleeves should enable measurement of the RH within the centre of the slab, and RH towards the edges of the slab and near internal walls, as tests conducted by the ATC have proven to return varying RH within these different zones.

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Practical Issues Although this seems to be the most reliable test, there were issues with the actual sleeve mechanism that could potentially affect its performance. Firstly, on a number of occasions the sleeve was damaged as it was being inserted into the concrete slab. The way the sleeve works is that it has one hole punched in it so that it is open to a certain depth within the concrete. The relative humidity reading is appropriate to the depth at which this hole is punched. If the sleeve is damaged and moisture is also able to pass into it at a depth other than the hole, the test readings will be void. The second concern is the design of the cap and seal mechanism. In order to seal the sleeve there are two washers, one rubber and one plastic, which the sleeve cap slides into. The rubber and plastic washers, however, are fitted within, but not fastened to the sleeve and often become dislodged by the removal of the RH probe after taking a reading. This renders it impossible to reliably seal the sleeve again or to enable subsequent tests to be carried out accurately. The main problem with this test, however, is that the cap and upper lip of the sleeve sit slightly above the slab for ease of access to take readings on subsequent visits. On a construction site, where various tradesmen are coming and going, the sleeve is exposed and the ATC experienced instances where the cap was knocked off between visits, or the cap and lip had been sheared from the sleeve, rendering the mechanism useless. It must be noted here that problems experienced were with one brand and other brands of sleeve available may not have these same issues. If used with care and protected from events on site, the Relative Humidity Sleeve Test has proven to be the most accurate of the relative humidity tests. The main advantage of using the relative humidity sleeve testing method is that most of the kit is reusable. The plastic sleeve that is inserted into the concrete can be returned to as many times as is necessary to obtain an instant reading of the concrete’s relative humidity value any time it is required. The relative humidity sleeves only need to stand for 72 hours before the initial reading is taken. After this period, subsequent readings can be taken instantly without the need to wait, as long as the sleeve’s cap remains in place. Another advantage is that measurements are taken from deep within the slab, which significantly minimises the impact of ambient temperature and relative humidity conditions.

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Image 3: Humidity Sleeve with cap and washers. Summary of Test As with trends overseas, it is predicted that the in-slab RH tests will be used more frequently in the future. In contrast with the Electrical Resistance in-slab test, Relative Humidity Sleeves are not affected by the presence of chemical admixtures, which means they are the most reliable form of in-slab RH testing. 3.23 Overview of Insulated Relative Humidity Testing Box During the testing period the box traps water vapour evaporating from the surface of the slab, causing the relative humidity in the air space to rise. As the humidity increases, the evaporation rate from the slab decreases and a point is reached at a particular relative humidity where no further evaporation occurs. The point where this equilibrium is reached is dependent on the moisture present in the slab16. The basic RH box in its present design does not seal well to the concrete slab. The relative humidity upper limit for installation of direct glue-down wood flooring is approximately 60%.17 Few of the relative humidity box tests conducted by the ATC returned RH values under this upper limit. It is assumed that this is a direct influence of ambient relative humidity and temperature conditions. Although the test results are not entirely reliable, the case study in Hawker Approach, Busselton, demonstrates the importance of conducting multiple types of tests on the slab. Where the capacitance meter gave readings between 3.2% and 4.7% - within the acceptable moisture limits for timber flooring – the humidity box returned a reading of 71%. Various sources claim that the readings obtained from the box method tend to be five per cent lower than with the sleeve method18, however the field testing conducted by the ATC shows a trend that opposes this assertion (Table 4). This is likely to have occurred as it has proven difficult to adequately seal the box to the slab with a non water-based sealant. Since it cannot be guaranteed that the boxes were sealed completely to the surface of the slab, it is likely that the

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relative humidity within the box had been affected by external atmospheric conditions. This is most obvious in the second round test result of Sherrington Road, Manjimup. Influencing Factors As mentioned above, this test is highly susceptible to the influence of external ambient temperatures and relative humidity. This method will only provide accurate results when the slab has been allowed to dry normally and does not contain chemical admixtures. It can therefore be assumed that the Humidity Box readings from Broome and the South West have some inaccuracy.

Image 4: Unable to reliably seal the humidity box to the concrete slab, pieces of timber have been used in this site in Broome to prevent ambient conditions affecting the humidity within the box. With a final reading of 91.4% RH, we can assume that this ‘technique’ was not successful.

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3.24 Overview of Rapid Relative Humidity (RH) Probes As written in the Literature Review by the ATC (see Appendix item 2), the Rapid RH Probe is promoted as a ‘small and rugged’ device which combines a moisture sensor, power supply and display all in one unit that is composed of a tail and head portion. The head portion contains a digital display which provides the viewer with a visual indication of sub-surface relative humidity and temperature. The unit is intended to monitor the concrete’s moisture content and behaviour over a period of up to six years. There is no doubt that if this mechanism was not so prone to failure it would be one of the more useful tools for measuring relative humidity within the slab. The most beneficial aspect of this test is that, in theory, it should be able to take a reading of the relative humidity within the slab instantly, and at any time required. The battery is also meant to last for up to six years. Unfortunately only one out of seven of the RRH probes still functioned on the third round of testing. As each probe costs $70, the ATC does not recommend this as a reliable or efficient test for gauging relative humidity within the slab over time. Results Within the first round of testing the Rapid Relative Humidity Probe results were within 3% of those of the Relative Humidity Sleeves (Table 4). During the second round of testing it became obvious that the Probes are not yet reliable enough to be considered a serious frequent testing option. Influence of External Factors During testing we found that the screen on the probe is very fragile and it is likely to become damaged as the probe is being inserted into the hole – this occurred on two occasions. On an additional two trials the probes gave satisfactory readings, however, when returning to them at a later date one of the probes returned an “error” reading, while the second did not turn on at all.

Image 5: Wagner Relative Humidity Probe embedded in concrete. Summary There are very few suppliers of Rapid RH probes in Australia. The initial cost for the whole kit was $1210. With an ongoing cost of $70 per probe, and a presumably low success rate, it is

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highly unlikely that a floor layer, without expertise in the area, would be willing to bear such a cost, or that this method of testing will become popular in Australia while other less expensive and more reliable methods are available. 3.25 Overview of Electrical Resistance Probes The resistance testing on the concrete slabs has been carried out using a Bollman BES Combo 100 resistance meter. As mentioned in the Literature Review by the ATC (see Appendix 2), this meter works by relating the moisture content to the conductivity of the concrete between two sensing probes that must be placed 200 mm apart, as the conductivity of the concrete is proportional to its moisture content. If the concrete has high moisture content, then its conductivity will increase and this will result in a high moisture reading. The greatest advantage of this test is that it is far less susceptible to fluctuations in ambient weather conditions than most of the other testing methods, as the probes can be inserted deep into the concrete. Many resistance meters have numerous calibration settings that allow the instrument to be used to determine the moisture content in various building materials. A failure to ensure that the meter is calibrated to test on concrete will render inaccurate readings. The manufacturers of the meters recommend for that meters should be serviced once a year to maintain accurate calibration, as repeated use without servicing is capable of producing inaccurate readings. Results None of the electrical resistance tests conducted by the ATC returned results greater than 2.6% moisture content. The electrical resistance test results collected by the ATC revealed that slabs reach fairly consistent moisture content shortly after being laid. This is demonstrated by the case study in Banu Road, Broome, which was tested at three weeks of age (Table 5) and returned results within 0.4% of the 20-year-old slab in Osmetti Drive, Kalgoorlie. Table 5(a): Electrical resistance test results. Site Age % moisture

content at 70 mm

% at 50 mm % at 20 mm

Banu Rd, Broome 3 weeks 2.6 2.6 2.2 Biny Lane, Broome 4 months 2.6 2.4 2.3 Scott St, Broome 3.5 months 2.5 2.2 2.1 Osmetti Dr, Kalgoorlie 20 years 2.5 2.2 1.8 Smyth St, Kalgoorlie 2 years 2.6 2.5 2.5 Sherrington Cres, Manjimup

3 months 2.5 2.5 2.5

Morgan St, Shenton Park

>20 years 2.5 2.5 2.5

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Table 5(b): Electrical resistance test readings as various depths of the slab. Site Reading at 70 mm

as % moisture content

Reading at 50 mmas % moisture content

Reading at 20 mmas % moisture content

Banu Rd, Broome 2.6 2.6 2.2 Scott St, Broome 2.5 2.2 2.1 Spoonbill Rd, Broome 2.5 2.5 2.2 Osmetti Rd, Kalgoorlie 2.5 2.2 1.8 Smyth St, Kalgoorlie 2.7 2.1 2.3 Lincoln St, Vasse 2.5 2.5 2.5 Sherrington Cres, Manjimup

2.5 2.5 2.5

Australian Standards suggest that the slab is ready to receive flooring when the probe gives a moisture content reading of less than 5.5%19. Our tests responded with consistent results of around 2.5% which indicated that the slab is ready for flooring to be laid. However, different tests on the same slab have provided results which suggest otherwise. For example, although the resistance probe results for Scott Street, Broome, are well within the acceptable moisture content range for the application of timber flooring, relative humidity probe readings for the same slab returned a result of 78.8%. External Influences Admixtures interfere with the conductivity of the concrete, and as a result any readings obtained through the use of a resistance meter on a concrete slab that has had admixtures added to it cannot be considered to be entirely reliable. Within Western Australia we believe the resistance meter can only be reliably used in Perth, where because of the moderate climate it is quite unlikely that concrete admixtures would have been used. Test results from Broome and Kalgoorlie are somewhat erratic which the ATC considers a consequence of testing concrete containing chemical admixtures. Summary of Test When testing on normal Portland concrete, the ATC research group agrees that the Resistance Probe gives a good overall indication of the behaviour of the moisture in the concrete. The greatest advantage is that the test can be performed at various depths and allows a profile of the moisture condition of the slab to be created, thus giving an indication of the long term moisture situation that will exist when the moisture level within the slab reaches equilibrium20. However, ATC results favour the Relative Humidity Sleeve for reliability.

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Image 6: Bollman Resistance Meter and Probes. The probes are placed within 8 mm holes, to any depth within the slab and 200 mm apart, to measure the conductivity of the concrete. 3.26 Overview of Capacitance Meter Test Although electrical resistance meters have been used for many years for testing concrete within Australia, “capacitance meters are now becoming more popular”.21 Capacitance meters provide an immediate reading of the moisture content within the upper 50 mm depth of the concrete slab only. As they are a spot-check they give no indication of long term moisture conditions and “there are no flooring or adhesive manufacturers who will accept this method as a “go or no-go” test for installing resilient flooring over concrete”.22 As with all other tests, the capacitance meter should be used in many different locations over the slab to better understand moisture behaviour. The meter should be used to take readings from the centre of the slab, the edges of the slab and near internal walls. It should also be used to observe the difference between areas of the slab receiving direct sunlight, and those which do not. Results The accuracy of this method of testing is overall questionable. The greatest difference noted was from the slab in Hawker Approach, Busselton. A test in the centre of the slab returned a reading of 3.2%, whereas a test closer to an external wall had a result of 4.8%. As it is recommended that a slab is ready for flooring if it has a moisture content of 5.5% or less, the slab in Hawker Approach would be deemed ready for flooring. It would be expected, however, that if timber flooring was laid directly to the slab, the timber would behave differently over its entirety as a reflection of the varying moisture content within the slab23.

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Electrical capacitance meters relate the moisture content to the measured electrical AC impedance. Admixtures interfere with the conductivity of the concrete, and as a result any readings obtained through the use of a capacitance meter on a concrete slab containing admixtures cannot be considered to be entirely reliable, they can, however, be used for qualitative comparison rather than quantitative. Below is a table of moisture vapour evaporation rates against average capacitance meter results over six sites north of Perth (Table 6; Figure 1a, 1b). All sites were within 1 km of each other, and all floors were to receive flooring within one to two weeks of testing. The ambient relative humidity over the testing period did not exceed 60%, and the temperature was typical of fine winter weather in Perth – maximum average temperatures of 19°C and minimums of 8°C. Table 6: Comparison between MVER and capacitance meter readings in six different sites. Site MVER (g/m²) Average Capacitance

Result (%) 1 334.1 4.6 2 331.6 3.6 3 236.8 4.2 4 344.4 5.4 5 295.7 4.5 6 353.3 4.6

Note: all slabs are within the recommended limits for the application of timber flooring.

Figure 1(a): Rate of moisture vapour evaporation measurements.

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Figure 1(b): Capacitance meter readings of six tests on concrete. It is evident from the graphs above that there is no strong correlation between MVER testing and relative humidity testing. 3.3 Test Summary and Recommendations Site Applicability All tests, other than the Bollmann electrical resistance test, will report true results if set correctly and when tested at in-service conditions. The electrical resistance and capacitance tests should not be considered to give accurate results in any location other than the Perth metropolitan area due to the influence of chemical admixtures on results. These tests can be used to gauge a qualitative (rather than quantitative) idea of moisture behaviour within the slab when chemical admixtures have been used. Calcium chloride and relative humidity box tests will all be affected significantly by the ambient temperature and the relative humidity of the immediate location and should only be utilised when the building is at, or following the “lock-up” stage of construction. Ideally all tests should be conducted 48 hours after the building has been running at in-service conditions (especially when HVAC systems will be in use). Test Usability and Reliability The tests requiring drilling of holes into the slab (humidity sleeve, rapid relative humidity probe, and electrical resistance tests) are considered to less ‘user-friendly’ than the surface tests. However these sub-surface tests will inevitably give a more accurate and more useful result than the humidity box test. The calcium chloride, or MVER test, is not comparable to the other tests as it is a measure of the flow of moisture from the slab rather than the amount of moisture within the concrete. It is an easy test to conduct, and if it is to be used it should be run in conjunction with one of the in-slab relative humidity tests or an electrical resistance test to adequately illustrate the behaviour of moisture within the slab.

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Recommendations Arising from Research by the ATC

• All slabs should be tested by various methods, including testing for moisture vapour evaporation rate and in-slab relative humidity.

• Each test then needs to be performed over various locations on the slab to ascertain the overall moisture behavior within the slab.

• Relative humidity sleeves should be used wherever possible, as they have proven to be the most reliable of the relative humidity tests.

• Tests should be conducted only when a building’s ambient relative humidity and temperature have reflected in-service conditions for at least 48 hours.

• Capacitance meters and electrical resistance tests will be affected by the presence of additives in the concrete mix. Relative humidity box results may also be affected.

• Rapid Relative Humidity probes are not recommended as they are likely to be damaged or stop functioning.

It must be kept in mind that different producers may use different additives and the concrete will behave differently. Table 7 summerises the results. Table 7: Test applicability, usability and reliability comparisons. Climatic Zone

Capacitance Meter

Electrical Resistance

Rapid Relative Humidity

Humidity Box

Humidity Sleeve

Calcium Chloride MVER

Perth – Moderate Climate

Fair Good Not reliable*

Fair Good Not reliable^

Broome – Tropical Climate

Not reliable (concrete additives)

Not reliable (concrete additives)

Not reliable*

Fair+ Good Not reliable^

South West – Moderate Climate

Not reliable (concrete additives)

Not reliable (concrete additives)

Not reliable*

Fair+ Good Not reliable^

Kalgoorlie – Hot / Dry Climate

Not reliable (concrete additives)

Not reliable (concrete additives)

Not reliable*

Fair+ Good Not reliable^

Reliability Fair Good Bad Fair Good Fair Usability Easy Moderate Hard Easy Moderate Easy * Product is considered not reliable due to high initial set-up costs, and bad performance. ^ Test needs to be revised before more frequent use is encouraged. + Chemical admixtures may interfere with test results.

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4.0 What Deems the Slab Ready to Accept Timber Flooring? There is much conjecture over the length of time it takes a concrete slab to dry to the point that it will not influence the behavior of direct-stick timber flooring. A laboratory study under ideal conditions found that a standard mix concrete slab took 46 days to dry to acceptable limits for flooring24. This is a considerably shorter length of time than the generally accepted three month standard. Often slab curing and slab drying are thought of as interchangeable processes. This is not true. Curing is the process by which a satisfactory moisture content and temperature must be maintained in order to ensure the quality of the hardened concrete. Curing aids in hydration, where a series of chemical reactions causes the cement to set. The curing period for a standard Portland cement mix generally takes five to seven days after cement has been poured. The length of time it takes concrete to dry is the length of time it takes the free water within the pores of the concrete to evaporate to an acceptable level for use. The Cement Concrete & Aggregates Association stipulates that this time is three months from the point of cement mix being poured. However, the length of time required for the completion of each process is complicated by many variables and differs from slab to slab. It is not reasonable to give a generalized time-frame. On the website for VCS Timber25 it is stated that for new slabs “concrete cures at a rate of 25 mm per month from the last time that the slab was wet. Therefore a 100 mm thick slab will require 4 months from the roof installation to reach a suitable installation point”.26 This supposition is flawed for the following reasons:

• It does not take into account the climate zone the slab is setting in. • It does not stipulate the concrete mix used. • It does not take into account any chemical admixtures which may have been employed.

Finally, it assumes the flooring will be installed on a newly laid slab. Concrete is considered to be one of the most moisture-sensitive construction materials – both during construction and in rewetting conditions, such as flood.27 The distinction between drying of a new slab and drying of mature concrete (after rewetting) must be made as research highlights that concrete maturation effects and changes the ability of concrete to transport water (moisture permeability). This is demonstrated though research conducted by Goran Hedenblad.28 In the article Drying Times for Concrete After Water Damage, Hedenblad tested well hydrated concrete specimens (either fully capillary saturated or saturated to 95 percent) more than a year old. His research found that rewetted mature concrete with a water-cement ratio of 0.70 and drying from one side took 515 days to reach 85% internal RH. To reach the same RH level, newly placed concrete with the same water-cement ratio took 184 days when cured for four weeks.29 This complements the recordings by the ATC on the study of a house in Shenton Park. The house had a new extension, and both the existing slab and new slab were to receive timber flooring. The drying time of the old slab, which had been exposed to rain during the construction period, was significantly longer than the drying time of the new slab. This emphasises the assertion that concrete slabs will continue to uptake and lose moisture (vapour) in order to establish equilibrium with the changing ambient conditions for decades after the slab has been laid.

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The datasheet Moisture in Concrete and Moisture-sensitive Finishes and Coatings30, produced by Cement Concrete and Aggregates Australia stipulates that “unless the relative humidity of the external environment is particularly low, the relative humidity in concrete will usually remain quite high after the majority of water has evaporated, typically about 75%”.31 The sheet goes on to recommend that “for any given relative humidity, the moisture content of concrete is far less than that of timber. This indicates that timber framing/materials can be placed directly in contact with the concrete as the lower moisture content of the concrete will not affect the timber (moisture content typically 10 – 17%)”. 32

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5.0 Influencing Factors on Flooring Behavior Other Than Concrete Moisture Content This section of the report deals with two case studies conducted by the ATC into failing floors in the Perth metropolitan region. It should be noted that neither of the slabs involved was new. Both studies highlight possible causes of timber failure other than a high slab moisture content.

5.1 Case Study Title: Cupping Floor in High Wycombe, Perth, Western Australia The case study floor in High Wycombe suffered from raised board edges throughout the affected floor area, although not every board had failed. On those affected, the edges had cupped +/- 3mm resulting in 1-1.5 mm gapping throughout the floor area. The slab had been laid approximately 17 years prior to the testing. The slab had been sandblasted in preparation for flooring with Jarrah boards fastened to the slab with Selley’s adhesive. Good building practices seem to have been followed when the house was constructed, so there is no reason to suspect that a moisture membrane was not laid prior to the slab being poured. Relative Humidity Sleeve and Box readings were 48.5% and 47.5% respectively, which translates to moisture content within the slab around the region of 1.5%. Many international authorities on concrete and moisture sensitive flooring suggest that it is not necessary to apply a vapour barrier over the concrete when its moisture content is below 2.5%. The moisture reading taken from the concrete at the residence in High Wycombe therefore discounts conditions underneath the floor as being the cause behind the failure of the floor. The peculiarities were that some boards had only lifted along one edge, and that the warping of the timber began prior to the use of the reverse cycle air-conditioning system. This discounted internal temperature and relative humidity as contributors to the timber failing. The moisture content readings of the Jarrah were also within expected moisture levels. Since the timber failing could not be attributed to higher than expected moisture within, or emitted from the slab, or the ambient temperature or relative humidity within the house, the ATC queried the adhesive used. It was thought that the Selley’s adhesive used may not have sufficiently allowed for the movement of the Jarrah floorboards. According to the Forest and Wood Products Research and Development Corporation33, adhesives have a significant effect on reducing expansion. Being a proprietary brand, it is reasonable to assume that the Selley’s adhesive used would be ‘plastic’ enough to allow the uptake and loss of moisture from the timber. As the varieties of failures within the flooring did not appear to be consistent with any typical cause of cupping, the ATC concluded that it was possible there was an inconsistent spread of adhesive when the boards were initially laid.34

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5.2 Case Study Title: Cupping Floor in Hillarys, Perth, WA The case study floor in Hillarys suffered from cupping and obvious expansion of floorboards in localised areas. Two key failures noted were; cupping in areas cooled by evaporative air-conditioning, and significant cupping of flooring in front of the fireplace. The nine-year-old 100 mm thick slab supported 12 mm East Coast Blackbutt flooring. The following table lists the Protimeter readings of timber moisture content over four locations within the house (Table 8): Table 8: Protimeter readings of 12mm East Coast Blackbutt flooring over four locations. Protimeter Readings

Timber Moisture ContentLocation 1 Location 2 Location 3 Location 4

Sample 1 13.4 12.5 10.6 10.6 Sample 2 13.8 12.3 10.8 10.7 Sample 3 13.2 14.8 11.8 Sample 4 10.6 12.8 Sample 5 11.3

Location 1: Bedroom 2 Location 2: Bedroom 3 Location 3: Main bedroom Location 4: Study

• In Location 1, all the samples tested apart from Sample 4 and 5 showed signs of cupping.

• In Location 2, Samples 3 and 4 showed signs of cupping whereas 1 and 2 did not. Sample 3 is heartwood and is visually darker. This may account for the substantially higher moisture reading.

• Samples from Location 4 showed no signs of cupping. Blackbutt is known to be highly responsive to changes in the ambient moisture conditions.35 It is important to note that the flooring in Location 1 began to fail one month after the evaporative air-conditioning was introduced. As the moisture content of the concrete slab was well within limits for timber flooring, it is assumed that the Blackbutt floor had been influenced by the increased relative humidity of the indoor conditions - a result of introducing evaporative air-conditioning. This then caused an increase in the overall flooring cover width. In Location 4, where the floor area is relatively smaller than the other spaces, it is likely that these dimensional changes had been accommodated by the space provided under the skirting board. However, in Location 1 and Location 4 the additional space afforded by the skirting board had proven to be insufficient. 5.3 Air-conditioning Timber is a natural product that responds to changes in ambient conditions. Just as timber will respond to changes in weather conditions (temperature and seasonal humidity)36, it will also react to artificial manipulation of the environment. However, as the changes are more exaggerated then natural environmental changes, the effect on floorboards will more apparent.

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Evaporative air-conditioners are colloquially referred to as “swamp coolers” in the United States due to the humid air conditions produced. The air supplied by a residential evaporative cooler typically has a relative humidity between 80% and 90%. Use of evaporative air-conditioners will ultimately cause timber to swell with uptake of moisture. The opposite is true for traditional air-conditioners. These work by removing moisture from the air; reducing the equilibrium moisture content. Moisture will be drawn from timber floorboards under these conditions, and the timber will ultimately shrink. 5.4 Ambient Environmental Conditions Minimum energy efficiency provisions have been incorporated into the BCA in recent years to eliminate poor practice from industry, and it is intended that they will help to reduce the greenhouse gas emissions made by the building sector. Areas singled out include building fabric, glazing, building sealing, air movement, and air-conditioning and ventilation systems. Particular emphasis has been placed on increasing the level of natural ventilation in Class 1 dwellings. In terms of our research, this means that the ambient temperature and relative humidity will never be at a constant, or able to be 100% controlled within the residential fabric. There will always be fluctuation enough to cause constant uptake and loss of moisture from timber flooring. This scenario will only be exacerbated if the timber is exposed to air-conditioning in intermittent periods.

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6.0 Timber Flooring As outlined previously, there are many reasons for timber flooring failure other than the slab having high moisture content. In some cases it has been demonstrated that it is the timber itself that has been prone to failure, rather than the influence of construction materials, or ambient climatic conditions, once the flooring has been laid. In the report Problems Associated with Installations – 80x12 Marri T&G Flooring37, Colin Reale investigated a number of failing floors for Bosch Timber Flooring. It was noted in all cases that the individual concrete sub-floors were found to be within the acceptable parameters for directly adhered timber flooring. Reale concluded that excessive stress within the timber was the most probable cause of failure. This was due to all of the problem floors being sourced from one mill during a period when the mill was experiencing problems with their kilns and drying procedures. Proper storage, acclimatisation and regard for internal relative humidity of the building are key components in ensuring that timber delivered with appropriate moisture content will not fail after it is applied to the slab. Data-Sheet 2 Pre-Installation Assessment38 produced by Timber Queensland, stipulates that “flooring should be delivered by the supplier with plastic wrapping (to top, sides and ends) in good condition in order to maintain the flooring at the appropriate moisture content”.39 It is necessary then to protect the timber from weather exposure and other sources of dampness. Many of the sites visited by the ATC had had timber delivered without having provision for proper storage (see Image 7).

Image 7: This photo was taken in Broome during the “dry season”. Heavy rain had fallen over the previous three afternoons. With just cloth and cardboard to protect it from the weather it is an example of how not to store timber flooring on site.

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Acclimatisation should occur when the building is at in-service stage of construction. Each flooring board needs to be exposed to the ambient internal environment (including heating or cooling systems) so as to find equilibrium moisture content with the internal conditions. If the timber has been stored as recommended then the process of acclimatisation can take as little as 48 hours. When “the moisture content of the timber flooring is close to the average in-service moisture content then subsequent seasonal changes in humidity will only result in small changes in moisture content”40 Occupants of the building need to have regard for the internal relative humidity of areas after flooring has been laid. Heating and cooling systems, refrigerators, direct sunlight and fireplaces can all create localised extremes in relative humidity around them, which can affect the moisture uptake and loss of nearby timber flooring.

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7.0 Concluding Recommendations It is not practical to put an absolute value on the length of time it takes concrete to dry to the point at which timber flooring can be applied. The ATC advises that it would be good practice to follow Cement Concrete & Aggregates Australia’s three month recommendation. After this period a number of tests must be conducted on the slab to gauge the movement of moisture and to calculate the moisture content of the slab. It is supported by the research conducted by the ATC that the most accurate and reliable method to measure the moisture content of the slab is though an in-slab relative humidity test. The relative humidity sleeve test has proven to be the most accurate and least vulnerable to influence by external temperature, ambient relative humidity conditions, or chemical admixtures in the cement mix. Hedenblad concluded his research by stating that drying “often takes so long that practical drying of the structure may be hard to do”41. If moisture content assessment is too difficult then it may be more efficient and cost effective to install a moisture barrier between the concrete and timber flooring. This should only occur after the three month drying period. Any timber flooring failure after this point is more likely to be attributed to fluctuation of the internal relative humidity of the building when in-service.

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Appendix 1 Measuring Moisture Levels in Concrete Slabs In order to determine when a concrete floor is ready to accept a moisture sensitive floor finish such as timber flooring, it is important to carry out tests to establish the moisture levels in the concrete and the rate of moisture migration through the slab, if any. Bulleyment advises to first carry out simple qualitative testing, which indicates whether moisture is travelling through the slab before embarking on more accurate quantitative testing methods which will actually measure the moisture content of the slab.42 Qualitative Testing Methods All the qualitative testing methods are based on covering the concrete surface with an impermeable material such as a rubber mat, glass or a plastic sheet or by applying the floor system to a test area of the intended floor finish for a suitable period of time. This system also has the advantage of testing the suitability of the adhesive used. Where a rubber mat or plastic sheet are used, a 500 mm x 500 mm square sheet of the membrane is taped down to the concrete for 24 hours and then the area is inspected for moisture, which will be evident from a darkening of the slab or even through the presence of condensed water drops on the underside of the membrane. Where a glass sheet is used, the concrete beneath is inspected for signs of moisture (darkening/water droplets) through the glass. The CCA [Cement and Concrete Association] has noted that the main disadvantage that should be kept in mind when using any of these testing methods is that moisture present underneath the membrane may have appeared as a result of condensation rather than moisture travelling through the concrete.43 The prospects of this kind of condensation occurring are dependent on the region and the seasonal and diurnal temperature conditions that pertain where and when the test is being carried out. This threat can be minimised [but not eliminated] by ensuring that the edges of the membrane are carefully sealed to the concrete surface. The CCA has also noted that care should be taken to distribute test locations evenly throughout the slab, avoiding areas subjected to sunlight and any other differential heat sources. Test locations should also be related to the area that can be placed from a single load of concrete. For example, since 5 m³ will cover 50 m² at 100 mm thick, there should be a testing location for every 50 m² of slab in this scenario.44 Quantitative Testing Methods A variety of methods can be used to determine the moisture content in a concrete slab. AS/NZS 2455 contains information for two testing methods to achieve this, the hygrometer which is the most popular method used in Europe, and the electrical resistance test. Other testing methods which will be discussed include the calcium chloride test and the gravimetric moisture content test.

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Measuring the Relative Humidity of Concrete

The relative humidity of a concrete slab can be determined by both surface and sub-surface methods in accordance with BS 8201/8203 and ASTM F 2170-02. The surface method (Image 8), which requires no drilling, involves the use of a humidity box that has an opening on its bottom surface. For a reading to be taken, this box needs to be sealed to the slab’s surface to enable the water vapour evaporating from

the slab to become trapped in the box. After about 16 hours, the pressure of the water vapour in the box reaches equilibrium with that in the slab and a relative humidity reading is taken. One of the most popular humidity boxes on the market is made up of a block of foam with a cavity in the centre of its bottom surface. A meter is required to obtain a reading of the relative humidity by inserting it via a lead into a hole in the box that goes through to the cavity. This hole is plugged during the 16 hour cover period. Another humidity box that is also on the market is composed of a well insulated PVC box that, in addition to the hole on its underside which traps the rising moisture, has a clear window on its top from which a reading can be taken.

The subsurface method, which is also referred to as the “in-situ” test (Image 9), involves drilling a hole in the concrete before inserting a humidity sleeve into it. This sleeve is capped flush with the top surface of the slab for a period of about 72 hours after which a relative humidity meter is connected to the probe to yield an internal relative humidity reading. As noted earlier, if the reading taken is less than 75% and deemed acceptable, then the slab can be considered

ready to receive a timber floor finish. If the reading is higher than 75%, then timber flooring manufacturers would recommend that the floor be left to dry out for a further period before being retested. When returning to the slab, another 16 hours waiting period would be necessary where the surface method is being used. However, in the case of the sub-surface method, no waiting time is necessary as long as the capped sleeve remains in place.45 If the age of the slab and the ambient conditions indicate that further time is unlikely to yield better results, then further investigations should be embarked on.

Image 8  

Image 9 

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Based on the idea of the “in-situ” test, the Construction Technology Laboratories together with Howard Kanare in the US have recently developed a moisture testing device called the Rapid RH relative humidity probe (Image 10). The small and rugged device which combines a moisture sensor, power supply and display all in one unit, is composed of a tail and head portion. The head portion contains a digital display which provides the viewer with a visual indication of the temperature and relative humidity of the concrete all at a touch of a

button. To obtain a reading, it is recommended to insert the probe into a hole drilled at least 40% of the concrete’s depth which not only gives an accurate indication of the concrete’s condition but also allows the device to fit level with the concrete thus preventing damage to the probe. After following ASTM F2170-02 procedures pertaining to stabilisation time, a reading can be taken. In testing the Rapid RH was shown to have a stabilisation time of 30 minutes to several hours depending on the concrete and conditions.46 An added advantage of the device is that it can be left in the left for up to six years during which it can be regularly consulted to give an indication of the moisture behaviour in the in the slab. The only major disadvantage of the device is that it is not reusable and needs to be disposed of after being removed from the slab. In all the above cases, the relative humidity test should be repeated in several different positions on the slab. Where the surface method is being utilised, substantial time can be saved by using more than one humidity box. However, where this is not possible, the CCA recommends covering the subsequent testing positions with an impervious membrane before the humidity box is transferred to the subsequent positions. This will speed up the later readings.47 Electrical Resistance and Capacitance Testing The electrical resistance test (Image 11) relates the moisture content to the conductivity of the concrete between two sensing probes that are placed about 100 mm apart. Where the concrete has a high moisture content, the conductivity of the concrete will be much greater which will result in a high reading. Electrical capacitance meters (Image 12), on the other hand, relate the moisture content to the measured electrical AC impedance. They are able to measure to a depth of about 51 mm as opposed to the electrical resistance meters whose probes enable it to typically measure to a depth of 200 mm. Suprenaut is of the opinion that electrical impedance meters are only useful for making a quick survey to determine positions in the slab that require more thorough quantitative testing to take place.48 He also suggests that the user of both the electrical resistance and impedance meters should check the manufacturer’s calibration procedures that accompany the meters to ensure that they are correct, as this could adversely impact the readings. The use of these meters in Australia has declined to some extent in recent years to the point where few suppliers seem to be promoting them, focusing instead on relative humidity apparatuses.49 The CCA has also shown a reluctance to fully endorse these meters as they have noted that the resistance of aggregates, reinforment chlorides and other additives that may have been added to the concrete mixture can influence the reading obtained.50

Image 10 

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Calcium Chloride (MVER) Tests

Although not commonly used in Australia, the National Ready Mixed Concrete Association (NRMCA) in the USA notes that this is the test specified by most floor covering manufactures in the USA.51 The calcium chloride (Image 13) test was developed by the Rubber Manufacturers Association (RMA) in the 1950s and is now published as ASTM F 1869. The test involves placing a measured amount of anhydrous calcium chloride in a cup under a plastic dome that is sealed onto the slab surface for

60 to 72 hours. During this time the calcium chloride crystals absorb the moisture vapour in the air beneath the plastic dome. After the exposure period, the testing kit is weighed again to determine the difference between the initial and final weights which is then used to calculate the moisture vapour emission rate (MVER). This is calculated from the increased mass of the calcium chloride, the testing time and the surface area beneath the plastic dome sealed to the slab’s surface. The formula for calculating MVER is:

Gain in weight (g) x 6144.9 T(hrs) For example, if a pre-weighed dish weighed 32.5 g and increased in mass by 2.9 g after having been placed on a slab for 64h, the MVER would be calculated as follows:

2.9 g x 6144.9 = 278 g/m² 64 hr In other words, the moisture emission rate is 278 g over a square metre area. In the above example, if the flooring material was to be timber, the manufacturer would not recommend its installation since the upper MVER limit that they would recommend would usually be around 170 g/m².52 Craig and Donnelly point out that it should be noted that if the calcium chloride test is carried out before doors and windows are installed or before HVAC systems have been activated, the resulting MVER will be different to that when the building is under its normal operating

Image 11  Image 12

Image 13 

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conditions.53 This is due to the fact that concrete is a hygroscopic material that will easily take in or give up moisture, depending on the conditions of its environment. It is therefore essential to ensure that the ambient conditions above the slab be as close as possible to those of the building’s anticipated operating environment when the test is carried out. ASTM F 1869 sets out the conditions under which the calcium chloride test should be carried out. The standard specifies that testing environments that aren’t under HVAC control should be carried out when the ambient temperature is 23.9 +/- 5.6°C and 50 +/- 10% relative humidity. The biggest criticism of the calcium chloride test has come from experts who believe that the test is merely an indicator of the moisture present only in the upper layer of the (13-19 mm) of the concrete slab.54 This assertion is indeed true in the case of uncovered slabs where a lower moisture content will be present in the top portion of the slab than in the lower regions. However, Craig and Donnelly have pointed out that once the slab is covered, the moisture will redistribute throughout the depth of the slab such that a higher moisture content will be detected in the upper region of the slab when a problem has been detected.55 The suggestion for moisture testing to only commence once the slab has been covered should therefore be taken seriously. Howard Kanare, however, has come out recently still debunking the notion that moisture in a concrete slab will redistribute throughout its depth once it has been covered. In an article published in September 2007, Kanare still portrays his belief that the calcium chloride test only determines a portion of the free moisture near the slab’s surface.56 If this test is to retain its credibility in the timber flooring industry, it is imperative that more research be undertaken to verify Craig and Donnelly’s claims regarding the distribution of moisture in a covered concrete slab. In addition to the standard calcium chloride test, Craig and Donnelly also suggest a modified method that will give an indication of the effect on the MVER once the slab has been covered and the building watertight. With this method, a 0.5 x 1.0 m area of the slab is completely cleared of any curing, sealing compounds or any other residue. Half of this area is then covered with an impervious material such as a sheet of plastic or rubber, which is sealed to the slab for a minimum of seven days. After the cover period, a calcium chloride testing kit should be placed on the previously covered portion of the slab while another kit is placed on the location that remained uncovered. A comparison of the results from the two test kits will indicate the changes in MVER that are likely to occur once the floor covering has been applied. To further complement this test, particularly where the MVER is found to be higher than the recommended level, Craig and Donnelly also advise that a relative humidity test of the concrete be taken using one of the relative humidity testing instruments detailed in this report. Such a test will help decipher whether the inability of the slab to reach the MVER necessary is due to ambient conditions or a high level of moisture content in the slab itself. Tramex Capacitance Meter “Concrete Encounter” Capacitance Meters work on the principle of electrical impedance measurement to give accurate non-destructive moisture readings. The electrical impedance of a material varies with its moisture content. It is measured by creating a low frequency alternating electric field between the electrodes. This field penetrates the material under test. The very small alternating current flowing through the field is inversely proportional to the impedance of the material. The instrument detects this current, determines its amplitude and derives the moisture content which is displayed by the instrument.57

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References 1 Northcote, K. H. with Beckmann G. G., Bettenay E., Churchward H. M., van Dijk D. C., Dimmock G. M., Hubble G. D., Isbell R. F., McArthur W. M., Murtha G. G., Nicolls K. D., Paton T. R., Thompson C. H., Webb A. A. and Wright M. J. (1960-68): 'Atlas of Australian Soils, Sheets 1 to 10, with explanatory data'. CSIRO and Melbourne University Press, Melbourne. 2 Australian Government Bureau of Meteorology – Climate of Western Australia, viewed on 13 October 2008, <http://www.bom.gov.au/lam/climate/levelthree/ausclim/ausclimwa.htm>. 3 Australian Government Bureau of Meteorology – Climate of Broome, viewed on 13 October 2008, <http://www.bom.gov.au/weather/wa/broome/climate.shtml>. 4 Moisture Testing of Concrete Slabs When 3lbs is not 3lbs. Peter Craig and George Donnelly. Concrete International, September 2006, P23. 5 Communication between Robyn Diggins (ATC) and Harry Backes, Manager of the Perth office for Cement Concrete & Aggregates Australia. 6 Moisture in Concrete and Moisture-sensitive Finishes and Coatings, Datasheet, Cement Concrete & Aggregates Australia. April 2007. 7 Ibid 8 Kanare, H., “Concrete Floor Moisture Tests”, in Concrete Construction Magazine, Chicago, USA, Sept 2007, viewed on 13 October 2008, <http://www.concreteconstruction.net/industrynews.asp?sectionID=700&articleID=560289>. 9 Ibid. 10 Kanare, H. Concrete Floors and Moisture, Portland Cement Association, 2005. 11 Ibid, p19 12 Ibid, p19 13 Common Questions Asked About Floor Slab Testing, viewed on 13 October 2008, <http://www.vaportest.com/Webpages/common_questions.htm>. 14 ASTM F 1869. See Literature review produced by the ATC for more detail. 15 Communication between Robyn Diggins (ATC) and David Hayward (ATFA), 2 October 2008. 16 Hayward, D., “Timber Flooring” Australian Timber Flooring Association (Version 1), 2005, p. 47. Appendix A3. 17 Ibid. 18 Testing of Concrete Moisture and Alkalinity, viewed on 13 October 2008, <http://www.floortests.com/moisture-alkali/testing/>. 19 Australian Standard, DR 99463 Timber Flooring – Part 1: Installation. (This is a revision of AS 1262 – 1972 and AS CA31 – 1960). 20 When a floor covering is placed on top of the slab, it restricts evaporation from the top surface and the moisture within the slab distributes itself to achieve equilibrium due to temperature and chemical interactions from the top to the bottom of the slab. 21 Communication between Patrick Beale and David Hayward 18 June, 2007. 22 Indoor Environment Connections newspaper, Volume 7, Issue 10 (August 2006). Produced by Indoor Environment Communications. 23 This assertion has been agreed with by Dr. Graeme Siemon. 24 Indoor Environment Connections newspaper, Volume 7, Issue 10 (August 2006). produced by Indoor Environment Communications. 25 VCS Products Introduction, viewed on 13 October 2008, <http://www.vcsproducts.com.au/index.php?controller=category&path=14_140_1401>. 26 Ibid. 27 Lezell, C., ‘Concrete: When Do You Know It’s Dry?’ in Restoration and Remediation Magazine, August 23, 2007. 28 Hedenblad, G., “Drying Times for Concrete After Water Damage”, The Swedish Council for Building Research, 1993. 29 Ibid. 30 Moisture in Concrete and Moisture-sensitive Finishes and Coatings, April 2007, Cement Concrete and Aggregates Australia. 31 Ibid. 32 Ibid. 33 Forest and Wood Products Research and Development Corporation - Media Release, 7th June, 2006 : Laying Down ‘Best Practice’ Recommendations for Timber Floors, pp 1-2. 34 This assertion has been agreed with by Dr. Graeme Siemon. 35 Hayward D., “NDTP Flooring Program, Technical Report No 2, Milestone No 2”, Timber Queensland, Australia (October 2003), pp 22-24.

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36 Hayward, D., Timber Flooring Australian Timber Flooring Association. December 2005. P13. 37 Report: Problems Associated with Installations – 80x12 Marri T&G Flooring. Prepared by Colin Reale on behalf of Bosch Timber Flooring. 38 Timber Queensland, Data-Sheet 2, Pre-Installation Assessment, Version 1, October 2005. 39 Ibid 40 Ibid 41 Hedenblad, G., “Drying Times for Concrete After Water Damage”, The Swedish Council for Building Research, 1993. 42 Bulleyment, A., “Hygrometer Take The Guesswork Out of Concrete Floors”, in Build, New Zealand (Mar / April 1999), p.41 43 “Moisture in Concrete and Moisture-sensitive Finishes and Coatings”, in Cement Concrete & Aggregates Australia, Mar 2007, p 7. 44 Ibid, p 7. 45 Capobianco, C. ‘ASTM F2179-02: A Concrete Moisture Testing Method’, in National Floor Trends, volume 6, issue 10, (Oct 2004), p 61. 46 Rapid RH Installation and User Manual, viewed on 13 October 2008, <http://www.rightergroup.com/docs/terroxyresinsystems-rapidrhinstallationandusermanual.pdf>. 47 “Moisture in Concrete and Moisture-sensitive Finishes and Coatings”, op-cit, p 7. 48 Suprenaut, B.A., “Moisture Testing Basics”, in Task Group on Moisture, ACI Committee 302, Strategic Development Council, p 6, viewed on 13 October 2008, <www.concretesdc.org/FloorMoisture/chapter_3_-_moisture_testing_basics.pdf >. 49 Correspondence between David Hayward and Patrick Beale, 17 October 2007. 50 “Moisture in Concrete and Moisture-sensitive Finishes and Coatings”, op-cit, p 7. 51 “Concrete in Practice, What, Why & How”, (National Ready Mixed Concrete Association, USA, 2004) p 2. 52 Calcium Chloride Moisture Test data sheet published by Papworths Pty Ltd Site Testing Equipment. 53 Craig, P and Donnelly, G. “Moisture Testing in Concrete Slabs: When 3lbs is not 3lbs”, in Concrete International, (American Concrete Institute, USA, Sept 2006) p 24. 54 The NRMCA report sited in this report also makes this assertion. 55 Craig, P and Donnelly, G. “Moisture Testing in Concrete Slabs: When 3lbs is not 3lbs”, in Concrete International, Op-cit, p 24. 56 Kanare, H. “Concrete Floor Moisture Tests”, in Concrete Construction Magazine, Op-cit, viewed on 13 October 2008, <http://www.concreteconstruction.net/industry-news.asp?sectionID=700&articleID=560289>. 57 Tramex Concrete Encounter 4, viewed on 13 October 2008, <https://tramexltd.com/pdf/CME4.pdf>.