1. Floor Screeding
Lesson no 1

3. 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

4. Types of floor screed systems
Bonded. (Monolithic.)
Un Bonded
Floating screed

5. 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

6. Bonded floor screed

7. 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.

8. Un Bonded floor screed

9. 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

10. Floating floor screed

11. Task
1. How much mixed material is needed to complete a floor screed m long by m wide
and m thick?
Answer
1 m3

12. Task 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

13. Answer

14. 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

16. 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

18. 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

19. Question Plastic sheeting below the structural floor is the:
damp proof membrane
vapour barrier
moisture trap
aid to curing the floor
Answer

20. Question The type of cement used in floor screeds is: Masonry Portland
Extra Portland
Rapid Portland
Ordinary Portland
Answer

21. 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.

22. 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.

23. 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.

24. 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
The mix ratio is 3 parts sand and 1 part cement

25. 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.

26. 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

28. 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

30. 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

31. Floor screeding Floor area is calculated by volume
i.e length x width x depth.
Length = 29m, x width = 30m, x depth = 0.035mm, = m3

32. Question How do we key a smooth floor to receive a screed Answer
With a scrabbling machine

33. 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

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

36. 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..

37. Task
Now work in groups to answer questions on pages 324 –326 of your work book

38. Floor Screed
Lesson no 2

39. 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

40. 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

41. 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

42. 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

43. 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

44. 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

45. 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

46. Water level

47. Water level

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

49. Laser level

50. Laser level

53. 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.

54. 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.

55. 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

56. 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.

57. Question What is a datum line Answer
A datum line is a level line around the room

58. 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

59. Task 2
Describe how to set up a floor with a fall

60. 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

62. 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

63. 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

64. Task
Now work in groups to answer questions1 –19 , pages 327 –335 of your work book
Then complete the word search

66. 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.

67. 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.

68. 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.

69. 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.