Floor Screeding

Lesson no 1

Learning outcomesby the end of this lesson you should be able to

Identify the bonded floor screed

Describe the monolithic floor screed

Recognise a Floating screed

Types of floor screed systems

Bonded. (Monolithic.) Un Bonded Floating screed

Bonded ( monolithic) floor screed

Bonded systems tend to be the most common methods it fits better with the nature of construction and the set and leave approach of concrete.

In this method a screed is applied to a previously laid concrete base

Bonded thickness is from 25mm to 40mm

Bonded floor screed

Un Bonded floor screed An unbonded floor is

where no bond to the concrete base is possible owing to its condition. Minimum thickness is 50mm.

A number of different forms of floor construction are included in this type, and are often grouped on their own, e.g. laying a screed on a damp-proof sheet membrane.

Un Bonded floor screed

Floating floor screed Floating screed • An Floating screed floor is

where no bond to the concrete base is possible owing to its condition. Minimum thickness is 50mm.

• A number of different forms of floor construction are included in this type, and are often grouped on their own, e.g. laying a creed on a damp-proof sheet membrane, and laying a floor on a layer of insulation

Floating floor screed

Task

1. How much mixed material is needed to complete a floor screed 5.000 m long by 4.000 m wide

and 0.050 m thick?

Answer

1 m3

Task

Tools and equipment for floor screeding will generally include:

1. sweeping brush, trowel, float, mixer, shovel2. splash brush, small tool, gauger, trowel, float3. spirit level, trowel, buckets, mixer, float4. levelling equipment, trowel, float, shovel

buckets, mixer Answer 4

Answer

Types of materials used

Mixing is one of the most important jobs of the whole operation

The quality of the sand is important and must be sharp,gritty and clean

The mix ratio is 3 parts sand and 1 part cement

Types of materials used

Some floors are laid using granite chipping

On large work , a pump mixer can be used.this will increase productivity and ensure an even mix

Preparation of floors

Remove all loose particles and high points on the floor

Brush all the area to remove dust For certain floor surfaces , a mix of

cement slurry and P.V.A can be brushed into the surface

Smooth surface should be scrabbled to form a key

Question

Plastic sheeting below the structural floor is the:

1. damp proof membrane2. vapour barrier3. moisture trap4. aid to curing the floorAnswer 1. damp proof membrane

Question

The type of cement used in floor screeds is:

1. Masonry Portland2. Extra Portland3. Rapid Portland4. Ordinary PortlandAnswer Ordinary Portland

Finishes

• Floors are generally finished with either a floated or trowelled surface.

• A wood fl oat produces a sand-faced texture.

• Trowelling gives a smooth finish which closes in the surface of a wood fl oat finish.

• Power floats, tampers and rollers can be used to assist the floor layer.

Finishes

Float finish These are laid mainly to receive mastic asphalt, asphalt

tiles, bitumen, concrete tiles and other heavy finishes. Trowel finish These are laid mainly to receive carpet, hardboard, vinyl

and cork tiles.

Task make a copy of this chart

CAUSE EFFECT

Poor preparation of sub-base. Cracking and lack of bond.

Mix too dry. Hard to lay; gives weak finish.

Too much cement. Shrinkage cracks.

Too little cement. Will break down when load applied.

Too much water. Hard to form flat surface; may shrink and be weak.

Poor material mix. Could leave pockets of sand with no cement, or vice versa.

Over-trowelling/trowelling too soon.

Brings water to the surface with cement.

Poor curing. Weakens surface.

Over-trowelling/trowelling too soon.

Brings water to the surface with cement.

Questions

What is one of the most important jobs in the whole operation

Answer Mixing is one of the most important

jobs of the whole operation What is the mix ratio of a floor screed Answer The mix ratio is 3 parts sand and 1 part

cement

Curing

It is essential that sufficient moisture is available for the continued hydration, or setting action, between the Portland cement and water for up to seven days after laying.

This is achieved by restricting the moisture loss of evaporation from the mix by covering

the finished topping with: Building paper. Polythene sheets. Damp hessian sacks.

A floor scrabbling machine

How do we key a smooth floor to receive a screed

Answer With a scrabbling

machine Basic floor Scrabbled floor Scrabbling machine

Grinding High Spots

The screed is ground using a power operated grinding machine.

Throughout the process the surface is kept wet.

Any ground material is removed using squeegees or some modern grinders collect the material as they operate

Question

How should we prepare the floor to receive a screed

Answer Remove all loose particles and high

points on the floor Brush all the area to remove dust

Floor screeding

Floor area is calculated by volume i.e length x width x depth. Length = 29m, x width = 30m, x

depth = 0.035mm, = 30.45 m3

Question

How do we key a smooth floor to receive a screed

Answer With a scrabbling machine

Monolithic floor screed

Monolithic in construction terminology means 'one body' or 'laid as one'.

That is to say when materials such as a concrete base and its screed are laid within three hours, they are deemed to be laid as one

Monolithic thickness is from 10mm to 15mm

Question

Name the three types of floor screed Answer Bonded (Monolithic) Un-bonded Floating screed

Floor screeding

Monolithic thickness is from 10mm to 15mm

Un-bonded thickness is 50mm

Bonded thickness is from 25mm to 40mm

Separate Minimum thickness is 40mm..

Task

Now work in groups to answer questions 14-22 on pages 324 –326 of your work book

Floor Screed

Lesson no 2

Floor screedingby the end of this lesson you should be able to

Recall why we use a datum line, and how to set out levels

Understand the term Curing Be aware of common faults that might

occur when floor screeding

Recap on lesson no 1

Name four types of floor screed Answer Monolithic Bonded Un-bonded Floating screed How do we key a smooth floor to receive

a screed Answer With a scrabbling machine

Recap on lesson no 1

How should we prepare the floor to receive a screed

Answer Remove all loose particles and high

points on the floor Brush all the area to remove dust

Datum line

A datum line is a level line around the room

This can be drawn by using a sprit level , or a laser level, or a water level.

The height of the screed can be set from the datum line by using a builders square

Water level

The green pipe is filled with water .

Then with two operatives each take an end of the water level,

By raising the end of the water level up or down they will both reach a point where both reading are the same

At this point a mark will be made on the wall, this is a datum point,from which datum lines can then be drawn

Water level

Setting datum level to wall areas

Set the liquid container at a suitable height for working

Set adjustable gauge to zero at the level of liquid in container

Water level Move instrument rod 3

from station point 1 to point 2,3,4 in sequence.

Raise or lower the rod until liquid is at zero on gauge and then mark this datum point on the wall at each of the points 1 – 2

Join up station points to obtain level datum line

Water level

Water level

Laser level

The laser level will project a level line around the room it is located in

Laser level

Laser level

Battens levelled in.

Bays filled in working in chequer board batten.

An initial trowel as work proceeds and turn back when floor has ‘picked-up’ and give

final Trowelling up.

Dots levelled in.

Screeds ruled off dots in order indicated.

Bay filled in ruling off screeds.

Rubbing up and consolidating with a wood fl oat giving sand faced texture or when

trowel finish is required lightly Trowelling up fl oat finish.

Task 1

In your own word describe how to seta datum level for setting up a level floor

Make a sketch of a water level

Tools required for the task You will need the following

tools to carry out the floor screed:

• Flooring trowel. • Large fl oat. • Spirit level. • Gauger. • Large and small straight

edges. • Shovel. • Timber for dots. • Builders square. • Water or laser level.

Question

What is a datum line Answer A datum line is a level line around the

room

Curing

It is essential that sufficient moisture is available for the continued hydration ,or setting action

This is achieved by restricting the moisture loss of evaporation from the mix by covering the finish topping with

Building paper Polythene sheets Damp hessian sacks

Task 2

Describe how to set up a floor with a fall

Common faultsDusty Floors

This is a common problem. The surface of a floor begins to loose adhesion and does not resist abrasion well, the top layer of laitance (cement paste) turns to dust. This can be caused by :-

a) Insufficient curing of dryer mixes

b) Too much water in the concrete or screed mix

c) Lack of cement in the mix d) Too much fine aggregate

in the mix e) Weak aggregates in the

mix

Question

How do we let a floor cure Answer This is achieved by restricting the moisture

loss of evaporation from the mix by covering the finish topping with

Building paper Polythene sheets Damp hessian sacks

Question

Give me two reasons why a floor screed may become dusty

Answer Insufficient curing of dryer mixes b) Too much water in the concrete or

screed mix c) Lack of cement in the mix d) Too much fine aggregate in the mix e) Weak aggregates in the mix

Task

Now work in groups to answer questions1 –19 , pages 327 –335 of your work book

Then complete the word search

Floor with a fall

Fall are put in floor screeds to drain away water, i. e a shower room

Achieving a fall on a floor screed is not as daunting as it may first seem.

The secret is in the preparation of the dots used to control the levels and thus the falls for the screeded area.

Achieving a fall

Achieving a fall on a roof screed is not as daunting as it may first seem. The secret is in the preparation of the dots used to control the levels and thus the falls for the screeded area.

Achieving a fall

On roofs, dots are started from the lowest outlet position and worked back and lined in to an agreed fall. The best way of achieving this is by the use of a fixed length rule or straightedge of known length.

Achieving a fall

For example, if a fall of 1:100 is required this is the same as 10mm in every metre. If you have a 3m straightedge, then place a packing piece 30mm thick (10mm x 3m length) below one end. You will find when you level the straightedge using a spirit level, this will mean that from one dot to another will rise by 30mm - simple ! This technique can be used for whatever fall you need, just calculate the packing thickness.