form screeds and granolithic finishes

• Learning outcomes

• The purpose of damp proof membranes

• The recommended area of separate construction flooring that can be laid without an expansion strip?

• The thickness of a Monolithic floor

The materials used in granolithic work include granite chippings 6 mm to dust, and Ordinary Portland CementGranite chippings and cement are mixed by volume in the ratio5 parts to 2

Question

The purpose of damp proof membranes is to:

Answer

prevent damp rising through the structure

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13 14

What is the recommended area of separate construction flooring that can be laid without an expansion strip?

Answer

14 square metres

Expansion strip

form screeds and granolithic finishes

• Monolithic 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 within 3 hours of the base being laid

• Monolithic thickness is from 20mm

Monolithic

• An unbonded floor is where no bond to the concrete base is possible owing to its condition. Minimum thickness is 75mm.

• 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 screed • • An Floating screed floor is

where no bond to the concrete base is possible owing to its condition. Minimum thickness is 65mm.

• • 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

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

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, which is know as laitance

Poor curing. Weakens surface.

• Learning outcomes• The use of a storey rod • How to form Granolithic coves• Why riser boards are cut to a splay:

Nosing line

Floor line

Spirit level

Storey Rod

Straight edge resting on nails

Nails

Tread Riser

Fix riser into position

Fix bottom riser

Use a long straight edge to line in other boards

Total Going

Total rise

Treads and risers are in the ratio of 2:1

I.e. for every inch you rise you tread,2inch

Riser of 6” = tread of 12”

Total going equal the proposed length of travel

Total riser equals the distance travelled from the floor

Stringer

Struts used to wedge stringer into position

Riser board

Fixing blocks

Fixing riser boards

Laying a granolithic staircase

• Set out• Fix riser boards and

stringer• Working on alternative

steps• Fill in the treads with

granate and trowel to a smooth finish

• When material has dried remove riser boards and fill in the missing treads

• Face up the risers

Struts

Stringer

Struts

• Coved cement skirting can be formed in cement/sand screeds and granolithic screeds. They are usually formed by running using skirting or coving trowels in conjunction with battens or screed grounds.