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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
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
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.
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
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
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
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
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..
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
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.
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
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.