Floor
Screeding
Lesson no 1
Learning outcomes
by 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 dampproof 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

1.
2.
3.
4.


Tools and equipment for floor screeding will
generally include:
sweeping brush, trowel, float, mixer, shovel
splash brush, small tool, gauger, trowel, float
spirit level, trowel, buckets, mixer, float
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:
damp proof membrane
2.
vapour barrier
3.
moisture trap
4.
aid to curing the floor
Answer
1.
damp proof membrane
1.
Question

The type of cement used in floor screeds is:
Masonry Portland
2.
Extra Portland
3.
Rapid Portland
4.
Ordinary Portland
Answer
Ordinary Portland
1.
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 screeding
by 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 faults
Dusty 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.