Felix Group Qatar

What is Floor Screed

Quality

Concrete is the most common base. The designer must establish the surface characteristics of

the slab and the normal thickness being allowed for the screed early in the design process. The

thickness will have a large influence on the make-up and method of laying, as well as the nature of

the bond. Screeds can be laid on timber but it must be stable and a good-quality damp-proof

course must be used.

Screed can achieve a high-quality finish with less than 3mm deviation over any 3m. The finish

material defines the quality needed. For thinner materials such as a vinyl less than 2mm thick, an

even and blemish-free finish is needed.

Material

Screed is usually a cementious material made from a 1:3 to 1:5 ration of cement to sand. A simple

cement and sand mix will be fine for a simple application but more sophisticated mixes are suitable for

a wider range of apllications. There are screeds that can be pumped in to place and are used to achieve

very level finishes thus allowing flexibility in laying.

Pumping the Screed

The sand, cement and water are mixed in the screed

pump machine and is then pumped via hoses to the

desired concrete area.

Spreading the Screed

The pumped screed is poured over the concrete

construction and divided with a floor wiper. In this way

the top-layer will be reinforced. The “semi-dry” screed

can be compacted and finished by simple hand methods

using a steel float or a screed board to give it a uniform

cover.

Screeding

The actual screeding process involves dragging a screed

board over the partially-compacted course material and

scraping-off the top layer to create a smooth, profiled

laying surface. After the screed has been spread,

compacted and screeded to level, it will be bull floated

or power trowelled.

Compacting & Finishing

Hand compaction of screeds may be carried out using a

screed board with a vertical chopping motion. The

compaction will be made much easier and more

efficient with the use of a hand rammer, a roller, or a

mechanical plate vibrator. A wooden or steal float may

be used to finish the screed. Steel trowels should not

be used until all bleed water has evaporated from the

surface.

After screeding

Bonding

Unbounded screeds ranging from 60 to 75mm thick can be laid at any time after the slab has been

constructed. They will usually have a damp-proof course separating them from the sub-floor. They

must be allowed to dry slowly, however, as fast drying will make them cure like a curly sandwich. If the

floor loading requires it, the screed may need reinforcement. This can be achieved either by the

addition of plastic particles to the mix or the use of one layer of fine reinforcement.

Services

Thicker screeds can be accommodate services,

but it is rarely a good idea to place these directly

in the screed. It is a better practice to feed pipes

and cables through a conduit, particularly heating

pipes, as these expand and contract. Typically,

the heating elements in underfloor heating

systems are surrounded by a specially designed

screed. This includes plastic reinforced pipes that

can flex with temperature and a screed

compound that will not crack even if relatively

thin.

Movement Joints

Movement joints must be considered as these

restrict the stress that can build up with the

material and control cracking. Ensure that any

building movement joints are mirrored in the

screed, too. No large areas or significant changes

in finish should be designed without a movement

joint so you will need to seek expert advice.

Shape should also be considered. Keep each area

of screed as rectilinear as possible and

incorporate movement joints at all changes of

level, structural elements and fixed points.

Curing

Screeds are cured as soon as possible after laying

by covering them with polythene sheeting. This

ensures that all the water remains in the mix

allowing the full strength of the screed to

develop. After curing, screeds should be allowed

to dry out naturally. Accelerated dying will

increase the probability of dying shrinkage cracks.

Cement

Cement is a binder that sets and hardens independently, and

can bind other materials together.

Sand

Clean and sharp sand is used. An excessively fine or dirty sand

will result in a screed of insufficient strength and durability with

increased drying shrinkage and curling.

The Mix

A sand:cement mix of 4:1 batched by weight is generally used.

For screeds of over 50 mm thickness, a concrete screed may be

used (10 mm maximum aggregate size). Such a screed would be

laid as would concrete, i.e. with a higher workability than a

sand/cement screed.

Screeding Process

Services

Screeds can be bonded to the sub-floor or unbonded.

Bonded screeds are laid directly to the new sub-floor or

chemical agent is applied before laying to ensure a good

bond. This ensures the screed acts as one with the slap

below. However, the laying process must be

undertaken carefully to ensure de-bonding does not

occur this will make the screed unstable and it will fail.

Usually, thinner screeds are bonded. An unbounded

screed of less than 50mm must be designed using a

specific mix to ensure it is strong enough.

Pouring Floor Screed into the Screed Pump

Screed thickness & moisture control

The moisture in a new screed needs time to evaporate.

Especially screeds more than 10mm thick contain large

quantities of water that needs to dry out. Otherwise

they can cause significant disruption late in the build

process. Moisture content is important, as most floor

finishes and adhesives are sensitive to it. They are also

sensitive to the build-up of water vapor if it is sealed in

to the screed. This has resulted in the development of

screed compounds that chemically control the water

used. Optimum screed thickness is from 30 to 70 mm as

there are a large number of sophisticated and versatile

compounds available for this range.

Screed Machines

See here for our screed pumps and other

equipment used for the screeding process.

You can check out as well as all our other

equipment and machines for our other services.

A screed is usally a mix of cement, water and

sand laid over a concrete base to provide a

surface close to a specified level. To achieve a

good-quality solid flooring, the use of screed is

needed. In many cases, it is not desirable or

practical to apply the floor finish directly to the

structure. So a screed is applied to create a

smooth, level surface. Screeds can also be used

to enclose heating elements or as a path to route

services.

Three basic criteria are at the heart of good

screed design: strength, bonding and moisture

control. With floor screeds, the standard of

materials and workmanship will greatly affect the

quality of the final material.