A floor screed is usually a cementitious material made from a
1:3 or 1:4.5 ratio of cement to sharp sand. It may be applied onto
either a solid in-situ concrete ground floor slab or onto a precast
concrete floor unit.
The screed may be directly bonded to the base,
with a minimum thickness of 40mm, laid unbonded onto a suitable
damp proof membrane which is placed over the slab, with a minimum
thickness of 50mm, or, if containing underfloor heating pipes a
minimum of 65mm thick.
Alternatively it may be applied as a floating
finish over a layer of rigid insulation material where the screed
should be a minimum 65mm thick or 75mm if it contains underfloor
If reinforcement is required, this can either
be in the form of a fine metal mesh or fibres which are normally
The screed may be left as finished, or floated
to produce a smooth surface on which to lay the specified flooring
or finish. Screeds can also be used to enclose underfloor heating
pipes or as a path to route services.
Ready-mixed sand and cement screeds that are
factory-mixed and then delivered to site offer additional quality
assurance over site mixed screeds and offer a more consistent
Some manufacturers provide pumpable flowing
screeds which can achieve very level finishes. Most of these
screeds are anhydrite compounds and are based on a calcium sulphite
binder. They are quicker to apply than a traditional sand and
cement screed and may be applied to a minimum thickness of 25mm if
bonded, 30mm if unbonded, or 35mm if a floating finish is required.
They can also be used in conjunction with underfloor heating
systems where a minimum 30mm cover to the pipes is needed. Up to
2,000M²/day may be laid using these screeds.
It is important to note however, that
whichever type and depth of screed is specified, the decision
should be made early in the design process.
Guidance should be sought from BS 8204 which
is in several sections and covers a number of screeds, bases and