Floor finishes

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Non-structural floor screeds shall be adequate for the location and intended use, and provide a suitable background for floor finishes. Issues to be taken into account include:

  1. installation
  2. screed thickness
  3. screed over insulation.


Before screeding, background surfaces should be:

  • clean and free of debris (e.g. dust and gypsum removed); concrete should be wetted and brushed
  • suitably prepared to provide an adequate mechanical key, where bonded screeds are required, cement grouting or a bonding agent should be specified to provide adequate adhesion.

Damp proofing should be completed before screeding starts.

Screeding should not take place in weather conditions which could adversely affect the finished construction, and:

  • should be scheduled to allow suitable drying time before following trades
  • in hot or dry weather, precautions should be taken to prevent the screed surface drying out too quickly
  • in cold weather, screeds should not be installed (screed damaged by cold should be removed and replaced).

Non-structural screed should be:

  • installed to the specified thickness and provide an even surface, suitable for the intended finish in accordance with the relevant British Standards and the floor finish manufacturer’s recommendations
  • of a suitable sand cement mix (generally between 1:3 and 1:4½ cement:sand). Where deeper than 40mm, concrete may be used
  • (where the floor is to include a monolithic slab) installed within three hours of the concrete sub-floor being poured.
  • mixed using only proprietary additives that have been assessed in accordance with Technical Requirement R3
  • thoroughly compacted, where required by the design, using either a heavy tamper, mechanical compactor or vibrator.

Proprietary non-structural screeds should be installed in accordance with the manufacturer’s recommendations.

Surface sealers or hardeners should only be used in accordance with the manufacturer’s instructions.

Where services are bedded in the screed:

  • there should be a minimum 25mm of cover over the highest point of pipes and insulation
  • provision should be made for the thermal movement of water pipes
  • pipes should be protected against chemical attack (e.g. by using purpose-made sleeves or ducts).

Non-structural screed over underfloor heating should:

  • be sub-divided into bays not exceeding 40m², with a maximum length of 8m, or installed per room
  • have expansion joints which are consistent with those in the slab.

Where concrete floor slabs are to serve directly as a wearing surface without an additional topping, they should be in accordance with BS 8204-2 and power floated.

Completed floor finishes should be protected against damage from traffic.

Standards relevant to screeding include:

BS 8204‘Screeds, bases and in-situ floorings. Code of practice’.
BS 8201‘Code of practice for installation of flooring of wood and wood-based panels’.
BS 8203‘Code of practice for installation of resilient floor coverings’.

Non-structural screed thickness

Thickness of cement and sand screeds should be in accordance with Table 2.

Table 2: Thickness of non-structural screed

Method of layingMinimum thickness at any point (mm)
Installed monolithically with base12
Installed on, and bonded to, a set and hardened base20
Installed on a separating membrane (e.g. 1000g polyethylene)50
Installed on resilient slabs or quilts (screed reinforced with wire mesh)65
Above services, reinforcement or insulation to services25

For concrete ground-bearing floors, a maximum 20mm monolithic screed may be acceptable as part of the required thickness.

Screed over insulation

Where screed is to be installed over insulation, the screed should be reinforced, and the insulation should:

  • provide adequate compressive strength to support wet construction screeds and floor loads
  • be tightly butted and, where required, turned up at perimeters to prevent cold bridging
  • be separated from the screed by a membrane (the membrane should be compatible with the insulation, and have joints lapped and taped, and be turned up at the perimeter).

Sound insulating floating floors should be in accordance with building regulations.