Floor finishes

9.3

9.3.5Ceramic, concrete, terrazzo and similar tile finishes

Tile flooring shall provide a suitable wearing surface for the location and intended use.

Before tiling is started:

  • ensure that the substrate is sufficiently dry (generally, six weeks for concrete bases and three weeks for screed is adequate)
  • ensure the substrate is reasonably true and flat (±3mm using a 3m straight edge), and installed to falls where required
  • differences in level should be dubbed out
  • the surface should be clean and free from laitance, dirt, dust, grease and materials incompatible with the adhesive.

Where a Calcium sulphate (Anhydrite screed) is used:

  • ensure that the substrate is sufficiently dry. Calcium sulphate screeds generally should be allowed to dry at a rate of 1 day per mm of screed thickness for screeds up to 40mm thickness, and 2 days per mm for any additional thickness over 40mm, however it should be ensured that the moisture content does not exceed 75% RH before tiling begins.
  • the weak layer of laitance which forms on the surface of the screed should be removed.
  • the screed should be sealed with an appropriate primer in accordance with the manufacturer’s recommendations.

When installing tiles to floors:

  • they should be bedded on a solid bed of mortar or proprietary adhesive, of a thickness appropriate for the material
  • the manufacturer’s recommendations should be followed where proprietary adhesives are used
  • they should be arranged to minimise cutting and to provide joints which are straight, neat, and of even width
  • accessories, such as covings and skirtings, should match the tile pattern, and be fixed so that joints are aligned with those in the floor
  • they should be installed with minimum 3mm joints, unless otherwise specified by the manufacturer.

Where tiles are to be fixed to a wood-based substrate:

  • the floor should be designed to take the additional loads of tiles, and any other materials (e.g. overlays)
  • they should be suitable for laying over a timber base
  • they should be bedded with deformable (flexible) tile adhesive, e.g. C2S1, and grouted in accordance with the manufacturer’s recommendations

Timber floor decking should be:

  • plywood for use in exterior conditions (minimum 15mm for joists at 400/450mm centres and minimum 18mm for joists at 600mm centres) screwed to the joists at 300mm centres with all square edges supported on joists or noggings (plywood should be installed with a 1.5-2mm movement gap between boards and at abutments, and be acclimatised to the room conditions and sealed on the underside and square edges, before laying, with a suitable sealer such as polyurethane varnish) or
  • chipboard floor decking overlaid with minimum 10mm plywood suitable for exterior conditions, acclimatised, sealed and fixed as previously indicated, or proprietary separating/decoupling layers, tile backer boards or tile bedding reinforcement sheets used in accordance with the manufacturer’s recommendations.

Movement joints should be:

  • provided around the floor perimeter and at rigid upstands, where tiled areas are wider than 2m
  • used to separate bays at 8-10m centers. Where underfloor heating is proposed the floor area should be divided up by intermediate movement joints into bays of size not greater than 40m2 with an edge length not greater than 8m
  • a minimum of 3mm wide unless otherwise specified by the manufacturer
  • provided on suspended floors where tiles continue over changes in the sub floor construction and flexing is likely to occur e.g. over a supporting wall where end bearings of beam and block joists may be found.

Grout should be:

  • cement-based epoxy resin or a proprietary product
  • water resistant, where tiles may become saturated.

Standards relevant to floor finishes include:

BS 8204-3‘Screeds, bases and in-situ floorings. Polymer modified cementitious levelling screeds and wearing screeds. Code of practice’.
BS EN 13748-1‘Terrazzo tiles for internal use’.
BS EN 14411‘Ceramic tiles. Definition, classification, characteristics, assessment and verification of constancy of performance and marking‘.
BS 5385-3‘Wall and floor tiling’.
BS EN 13888:2009'Grout for tiles. Requirements, evaluation of conformity, classification and designation'.