osmosis and the blistering of liquid applied … · osmosis and the blistering of liquid applied...

Osmosis and the Blistering of Liquid Applied Polyurethane Roof Membranes

Brian Hubbs, P.EngGraham Finch, MASc EITRob Bombino, PE

RDH Building Engineering Ltd. Vancouver, BC

BEST2 Portland April 2010

Background

Cold-applied asphalt-modified polyurethane waterproofing membranes

Commonly used in inverted roofing and waterproofing assemblies Very common in the Pacific Northwest and Western CanadaHistorical performance problems often attributed to poor details and/or inadequate thickness.

- Concrete Pavers or Ballast

- Pedestals (Optional)

- Filter Fabric

- Extruded Polystyrene Insulation (2-4")

- Molded Polyethylene Drainage Matt (Optional)

- Cold-Applied Polyurethane Roof Membrane

- Concrete Slab (6-8")

Background

Maintenance Manuals and Condition AssessmentsWater Filled Blisters:• Low thickness• Filled with water under pressure• Blisters vary in size from small (12mm) to entire roof or deck areas• No obvious detail or discontinuity • Pavers and ballast floating in some locations• Blistering observed over both conditioned (interior) and

unconditioned space (Parkade)• Blisters also observed on vertical planter walls and in water features• Top of membrane almost always wet when insulation removed

Two Different membrane manufacturersBuilding age varied between 3 to 12 years

2004 - Review of Roofs For Maintenance Manuals

Moderate Blistering

Typical Blister

Summary of Cut Tests

Minimum Thickness - CCMC Listing (1.5mm)

2004

10

12

12

2008

10

11

2008 - Large Blister Lifting Pavers

2008 - Membrane Blistering – Waterbed Effect

Membrane Blistering In Water Feature

Membrane Pore Structure – Membrane #1, 30 mil agedMembrane #1, 120 mil - NEW

Membrane #1, 30 mil - AGED

Possible Causes?

Details?No penetrations or adjacent detailsMembranes fully adhered except at blisters

Vapour Diffusion or Capillary Flow?large quantity and pressure of water cannot be explained by these mechanisms

Interior Sources?Vapour flow from membrane is always towards the interior

Pinholes and membrane?Not present at blisters.Water can not be contained under pressure

Hypothesis: Osmosis

What is Osmosis ?

The flow of water across a semi-permeable membrane from low to high salt concentrationRequires 2 things:

Difference in salt concentrationmembrane permeable to water molecules

Other Osmosis Research

Not well Documented by Building Industry Either rare or unreported

Other Industries:Fiberglass boat hulls• Uncured resins create a chemical osmotic cell leading to destructive

fiberglass hull-blistering

Epoxy Floor Coatings• Moisture from slabs on grade creates blisters beneath certain

membranes

Bridge decks• De-icing salts cause blistering of coatings

Could it be Osmosis ? - Is the Blister Water Salty ?

Blister water extracted and tested Contains high concentrations of dissolved metals:

Sodium: naturally occurring within cement and aggregatesPotassium: Potash commonly used concrete additiveSilicon: naturally occurring within cement and aggregates

Calculated osmotic suction pressures 300-400 kPa

Water extracted from membrane blisters was under pressure As blisters grow the membrane delaminates

Rainwater from the top surface of the membrane contained no relevant concentration of minerals

Vapour Permeance TestingAged 30-60 mil reinforced membranes removed from buildings

4 to 7 US perms (230 to 400 ng/Pa s m2) New membranes 90-150 mil membranes

0.3 to 2.0 US permsImportance of Inverted Wet Cup ASTM E96 Method

0

50

100

150

200

250

300

350

400

450

Dry Cup Wet Cup Inverted Wet

Cup

Vap

ou

r P

erm

ean

ce

ng

/Pa s

m2

Membrane #1 - 30 mils (Aged)

Membrane #2 - 60 mils (Aged)

Membrane #3 - 150 mils (New)

Impermeable Roof Membranes

(SBS, TPO, EPDM)0.00

0.10

0.20

0.30

0.40

0.50

0.60

Dry Cup Wet Cup Inverted

Wet Cup

Vap

or

Perm

eab

ilit

y

ng

/Pa s

m

Membrane #1 (Aged)

Membrane #2 (Aged)

Membrane #3 (New)

Impermeable Roof Membranes

(SBS, TPO, EPDM)6” Concrete

50% RH

Dry Wet Water

IWC

Looks like

an

inverted

roof ?

#1

Impact of Membrane Permeance

Use WUFI to simulate initial saturation or wetting of Concrete surface

Polyurethane – top 10 mm of concrete

Polyurethane – entire slab

SBS mod-bit – entire slab

SBS mod-bit – top 10mm of concrete

Laboratory Apparatus - Trial 5

Proof of Concept – Commercial Reverse Osmosis Membrane

Initial flow rates of up to 15 L/m2/day

Per manuf. specs

Measured Osmotic Flow – Control SamplesMembrane #1 - Controlled Salt Solutions - Osmotic Flow through Membrane

0

500

1000

1500

2000

25000

20

40

60

80

10

0

12

0

14

0

16

0

18

0

20

0

22

0

Days from start of test

Osm

oti

c F

low

th

rou

gh

Mem

bra

ne - g

/m2

Distilled Water - Control - No Osmotic Pressure

0.1 Molar Salt - 460 kPa Osmotic pressure

1.0 Molar Salt - 55,000 kPa Osmotic Pressure

Osmotic Flow – Blistered Membranes & Blister Water

Polyurethane Membranes #1 & #2 - Average Osmotic Flow through Membrane

0

500

1000

1500

2000

0

10

20

30

40

50

60

70

80

90

10

0

11

0

12

0

13

0

14

0

15

0

# of Days

Osm

oti

c F

low

th

rou

gh

Me

mb

ran

e -

g/m

2

Membrane Sample #1 - 30 mil

Membrane Sample #2 - 60 mil#2

#1

Osmotic Flow – Blistered Water & Control Samples

Osmotic Flow through Membrane #1 with Different Salt Water Concentrations

0

500

1000

1500

2000

0

10

20

30

40

50

60

70

80

90

10

0

11

0

12

0

13

0

14

0

15

0

16

0

17

0

Days from start of test

Osm

oti

c F

low

th

rou

gh

Mem

bra

ne - g

/m2 Membrane 1 - Distilled Water - 0 kPa

Membrane 1 - 0.1 M NaCl - 460 kPa

Membrane 1 - 1.0 M NaCl - 55,000 kPa

Membrane 1 - Blister Water - 326 kPa

Concrete Primer & Membrane Testing – New Membrane (150 mils)

Effect of Membrane Primer Type - Polyurethane vs Epoxy

0

50

100

150

200

250

300

350

400

0 20 40 60 80 100 120 140 160 180 200

Time (days)

Osm

oti

c F

low

th

rou

gh

mem

bra

ne - g

/m2

Epoxy Primer on membrane - 0.5 Perms

Polyurethane Primer on membrane - 0.9 Perms

Membrane Cured during first 50

days of testing. Permeance initially

2x5 times higher. Osmotic Rate

affected

0.4 to 1.0 g/ m2/ day

0

100

200

300

400

500

0 20 40 60 80 100 120 140 160 180 200

Osm

oti

c Fl

ow

-g/m

2

# days from start of test

M1-1 - 30 mil blistered




M3-1 - 120 mil new primed

M2-3 - 60 mil new

M3-2 - 100 mil new field applied

M4 - 100 mil new

Osmotic Flow Rate – All Samples

Aged Samples

New Samples

Results – Vapour Permeance and Osmotic Flow

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

M1

, B

1 (

Bli

ste

red

)

M2

, B

2 (

Bli

ste

red

)

M2

, B

3 (

Bli

ste

red

)

New

M1,

Un

pri

me

d

New

M1,

Ure

tha

ne

Pri

me

r

New

M1,

Ep

oxy

Pri

me

r

New

M2,

un

pri

me

d

New

M2,

wit

h A

lum

Pa

int

Co

ntr

ol

Me

mb

ran

es

0

1

2

3

4

5

6

7

8

9

10

11

12

M1

, B

1 (

Bli

ste

re

d)

M2

, B

2 (

Bli

ste

re

d)

M2

, B

3 (

Bli

ste

re

d)

Ne

w M

1,

Un

prim

ed

Ne

w M

1,

Ure

tha

ne

Prim

er

Ne

w M

1,

Ep

ox

y

Prim

er

Ne

w M

2,

un

prim

ed

Ne

w M

2,

wit

h A

lum

Pa

int

Co

ntr

ol

Me

mb

ra

ne

s

Permeance (US Perms) Osmotic Flow – (g/m2/day)

Pe

rme

an

ce (

US

Pe

rms

–H

igh

lo

w a

ve

rag

e)

Os

mo

tic

Flo

w –

(g/m

2/d

ay –

Hig

h L

ow

Ave

rag

e)

Blistered New

Blistered New

Is This Good Enough

to Eliminate Blistering ?

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Ne

w M

3, U

np

rim

ed

Ne

w M

3, U

reth

an

e P

rim

er

Ne

w M

3, E

po

xy

Pri

me

r

Ne

w M

2, u

np

rim

ed

Ne

w M

2, w

ith

Alu

m P

ain

t

Ne

w M

3 -

Fie

ld A

pp

lie

d

Ne

w M

4 n

o p

rim

er

Ne

w M

4, p

rim

er

1

Ne

w M

4, p

rim

er

2

Co

ntr

ol M

em

bra

ne

s

6" C

on

cre

te S

lab

Results – Vapour Permeance, Membrane vs ConcreteP

erm

ean

ce (

US

Pe

rms

–H

igh

lo

w a

ve

rag

e)

Reported Vapour Permeance of a 6

inch Reinforced Concrete Slab Varies

between: 0.05 and 0.2 US Perms.

Difficult to Measure.

Control membranes (SBS, EPDM,

PVC are all below the permeance

range of 6 inch concrete slab.

New 90mil membranes with primer

have much higher water vapour flow

rate through the membrane than

though the concrete. Is accumulation

and blistering still possible ?

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Ne

w M

3, U

np

rim

ed

Ne

w M

3, U

reth

an

e P

rim

er

Ne

w M

3, E

po

xy

Pri

me

r

Ne

w M

2, u

np

rim

ed

Ne

w M

2, w

ith

Alu

m P

ain

t

Ne

w M

3 -

Fie

ld A

pp

lie

d

Ne

w M

4 n

o p

rim

er

Ne

w M

4, p

rim

er

1

Ne

w M

4, p

rim

er

2

6" C

on

cre

te S

lab

…

Results – Osmotic Flow Through Membrane vs Concrete Vapour Flow

Estimated Vapour flow though a 6

inch Reinforced Concrete Slab in

g/m2/day.

Difficult to Measure.

Osm

otic F

low

–(g

/m2/d

ay –

Hig

h L

ow

Avera

ge)

Summary - Osmotic Blistering Process

Water on top of membrane almost year round in inverted roof

assembly (poor slope = more water)

Concrete is initially at or close to saturation. Vapour diffusion

moves additional moisture though membrane to concrete

interface.

Concrete is less permeable than membrane and water begins to

saturate the concrete and accumulate at the membrane

interface.

Mineral ions dissolve out of concrete increasing the salt

concentration of the water beneath the membrane. Osmosis

begins and small blisters are formed.

Vapour diffusion to interior through concrete is relatively

slow compared to the rate transported by Osmosis.

Blisters grow and expand due to osmotic flow.

Top surface of the membrane wet all yearMoisture moves though the membrane via vapour diffusion Concrete less permeable than the membrane = moisture accumulation Moisture dissolves minerals from concreteOsmosis forms small blisters at localized voids or debonded areas Osmosis continues expanding blisters over time - 3-6 mm of water per year

Is Osmotic Blistering a Regional Issue ?

• RDH Observations• West Coast of Canada• Pacific Northwest

• Discussions at NBEC 2009• Florida• Hawaii

• Discussions at RCI San Diego 2009

• Florida

• Appears to be more prevalent in temperate, humid climates

Next Steps

Determine maximum safe permeance threshold for inverted roofing and waterproofing membranesDevelop Osmotic flow test method and determine acceptable maximum flow rates.Revise Applicable Standards (ASTM C836-00 and CAN/CGSB–37.58-M86) to specify:

Maximum allowable inverted wet cup permeance (0.1 ?)Maximum allowable osmotic flow rate (1 g/m2/day ??)

Further testing of membranes currently on marketNeed solutions or further research to confirm performance:

Questions

osmosis and the blistering of liquid applied … · osmosis and the blistering of liquid applied...

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