NHBC Standards 2011

8.3 Floor finishes

SITEWORK STANDARDS

8.3 - S1 Sitework standards
8.3 - S2 Screeding
8.3 - S3 Ceramic, concrete, terrazzo and similar tile finishes
8.3 - S4 Asphalt finishes
8.3 - S5 Flexible sheet and tile finishes
8.3 - S6 Wood finishes
8.3 - S7 Staircase finishes

8.3 - S1
All sitework shall:
(a) meet the Technical Requirements
(b) take account of the design
(c) follow established good practice and workmanship
 


Sitework that complies with the design and the guidance below will be acceptable for floor finishes.

SCREEDING

8.3 - S2
Floor screeds shall be laid to provide a suitable background for the intended floor finishes
 

Items to be taken into account include:

(a) background

MOISTURE PROTECTION

Check that any specified damp-proofing treatment has been completed before screeding is commenced.

SURFACE PREPARATION

All surfaces should be clean and dust free. In particular, any traces of gypsum should have been removed. Concrete surfaces should be wetted and brushed before screeding.

BOND

Where screeds are to be bonded to the substrate, the surface should provide adequate bond. If necessary, the surface should be improved by:

  • hacking
  • roughening
  • grouting
  • application of a bonding agent.

(b) services

Provision should be made for:

  • thermal movement of water pipes
  • protection against chemical attack, for example by using purpose-made sleeves or ducts, see Chapter 8.1 'Internal services' (Design and Sitework).

There should be at least 25mm thickness of screed above the highest point of any service pipe or insulation placed around the pipe.

(c) mixing

Cement and sand screeds should be mixed in the specified proportions.

Proprietary screeds should be mixed in accordance with the manufacturer's recommendations.

(d) laying

WEATHER CONDITIONS

Screeding should not be carried out under weather conditions which could adversely affect the result. The following precautions should be taken:

  • hot or dry weather - screeds should not be laid in hot or dry weather unless precautions are taken to prevent the screed surface drying out too quickly
  • frost - screeds should not be laid if there is a risk of freezing.

Any screeds damaged by frost should be removed and replaced (reference should be made to Chapter 1.4 'Cold weather working').

TIMING

Monolithic screeds should be laid within three hours of the concrete sub-floor being poured.

Wet screeding should be programmed to allow sufficient drying out time before dry lining is to commence.

BAY SIZE

Screeds above underfloor heating should not exceed 40m2 with a maximum length of 8m.

THICKNESS

Screeds should be laid to the specified thickness.

COMPACTION

Screeds should be thoroughly compacted, using a heavy tamper or a mechanical compactor or vibrator.

Proprietary screeds should be laid in accordance with manufacturers' recommendations.

(e) protection, curing

Screed surfaces should be protected against damage from traffic and be kept continuously moist until sufficient strength has been attained to resist shrinkage stresses (at least 7 days).

(f) surface finish

SCREEDS PROVIDING A WEARING SURFACE

Floor screeds to be left as a wearing surface should be either treated with a surface hardener in accordance with manufacturers' recommendations or be power floated to a smooth and durable surface.

SCREEDS TO RECEIVE A FLOOR FINISH

Where a screed is to be used as a sub-base for a floor finish, the surface should be suitable for the required finish as specified in the design.

(g) screeds on resilient insulation materials

Screeds above resilient insulating materials should be laid on a separating membrane and reinforced as specified.

The slabs of resilient material should be tightly butted, and turned up at the room perimeter to prevent contact between the screed and the structure which could create sound transmission paths.

Joints in the isolating membrane should be lapped and taped. The membrane should be turned up at the perimeter to prevent grout seeping through.

Membrane turned up at perimiter 

(h) screeds on thermal insulation

The procedure for laying screeds on resilient materials should be followed. Turning up insulation at perimeters prevents cold bridging.

CERAMIC, CONCRETE, TERRAZZO AND SIMILAR TILE FINISHES

8.3 - S3
Tile flooring shall provide a suitable surface for the intended use
 

Items to be taken into account include:

(a) background

EVENNESS

The background to be tiled should be reasonably even and laid to falls where required.

PREPARATION

Before bedding is commenced, the following precautions should be taken:

  • the surface should be clean and free from all laitance, dirt, dust, grease and any other material incompatible with the adhesive
  • where appropriate, a damp-proof membrane should have been incorporated
  • differences in level should be dubbed out
  • the screed or concrete surface should be true and level (±3mm under a 3m straight edge)
  • the screed or base should be sufficiently dry.

(b) bedding

Cement and sand mortar should normally be a mix between 1 : 3 and 1 : 4½.

Where proprietary mortars or adhesives are used, manufacturers' recommendations should be followed.

(c) laying

Floor tiles should be bedded in a solid bed of mortar or proprietary adhesive of a thickness appropriate for the material. The tiles should be arranged to minimise cutting with straight joints of even width. Any cutting necessary should be done neatly and accurately.

(d) jointing

For ceramic tiles, joints should be not less than 3mm wide.

Movement joints should be provided around the floor perimeter and at rigid upstands. In large areas tiling should be divided into bays at 8-10m centres.

(e) grouting

Grout should be a cement based epoxy resin or a proprietary product. Where tiles may become saturated the grout should be water resistant.

TILES ON WOOD-BASED SUBSTRATE

The 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 noggins. Plywood should be laid 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
  • chipboard floor decking overlaid with minimum 10mm plywood suitable for exterior conditions, acclimatised, sealed and fixed as above, or proprietary separating/de-coupling layers, tile backer boards or tile bedding reinforcement sheets used in accordance with the manufacturer's recommendations.

Floor tiles on wood based substrates should be bedded with deformable (flexible) tile adhesive (e.g. C2S1) and grouted in accordance with the manufacturer's recommendations.

Tiles should be laid with minimum 3mm joints unless otherwise specified by the manufacturer. Movement joints should be provided at rigid abutments where tiled areas exceed 2m in length.

(f) accessories

Any accessories, such as covings, skirtings, etc, should match the tile pattern and be fixed so that joints are aligned with those in the floor.

(g) protection

Where necessary, tile flooring should be protected until the dwelling is handed over. Temporary covering should be building paper or an alternative material which will withstand traffic from other trades and any plaster droppings or other spillage.

ASPHALT FINISHES

8.3 - S4
Asphalt and pitch mastic shall be suitable for its use
 

Suitable thicknesses and grades include:

Use Thickness (mm) Grade
Floor finish 15 to 20 I or II
Underlay for other finishes in one coat 15 to 20 I or II

 
Suspended floor system manufacturers should be consulted where mastic asphalt floor finishes are to be used with such systems.

FLEXIBLE SHEET AND TILE FINISHES

8.3 - S5
Flexible sheet and tile floor finishes shall be laid to provide a suitable wearing surface
 

Items to be taken into account include:

(a) background

MOISTURE PROTECTION

The substrate should be sufficiently dry to prevent any adverse effect on the flooring.

Where applicable, manufacturers' recommendations should be followed.

EVENNESS

The surface should be even and without high spots or cracks. Where a levelling underlay is needed, it should be of a type and thickness recommended by the flooring manufacturer.

Boarded surfaces may be covered by a sheet underlay.

The following types are acceptable:

Type of underlay Minimum thickness (mm)
Hardboard 3.2
Plywood 4.0
Chipboard 9.0
Oriented strand board 6.0


(b) laying

CONDITIONING

Flexible and sheet flooring materials should be stored in a clean and ventilated place. Unless specifically permitted by the manufacturer, materials should not be stored in cold conditions. The temperature should be not less than 18°C for at least 24 hours before and during laying.

UNDERLAYS

Plywood or hardboard underlays should be fixed with ring shank nails or staples; and chipboard and oriented strand board with ring shank nails or screws, 2½ times the thickness of the boards.

Fixings for plywood or hardboard should be at 100mm centres at perimeters (12mm from edges) and 150mm centres across the sheets; and for chipboard and oriented strand board, at 300mm centres at perimeters (9mm from edges) and 400mm centres across the boards.

Measures should be taken to prevent damage to underfloor services.

FLOORING

Sheet or tile flooring should be fixed with the specified adhesives and in accordance with manufacturers' instructions.

Flooring should be fully bonded, where appropriate. Adhesives should be spread evenly, and dry and contact adhesives left for the correct period of time to ensure full bonding. Provision for adjustment after initial contraction or expansion should be made where necessary.

Welded joints should be provided, where specified, in accordance with manufacturers' recommendations.

The flooring should be pressed down firmly where appropriate, surplus adhesive removed, and the completed surface loaded or rolled as necessary to prevent curling or bubbling.

(c) fittings

Where specified, skirtings, coves, coverstrips and other pre-formed components should be fixed in accordance with manufacturers' recommendations.

(d) quality of finish

The floor finish should be reasonably level and smooth. Particular care should be taken at doorways and junctions. Flooring should be cut so that it fits neatly around fittings, pipes, etc.

(e) protection

All sheet or tile flooring should be kept protected until handover of the dwelling. Temporary covering should be building paper or other material, which will withstand traffic from other trades and any dampness caused by plaster droppings or spillage.

WOOD FINISHES

8.3 - S6
Wood flooring shall be laid so as to be suitable for the intended use
 

Items to be taken into account include:

(a) moisture protection

For wood finishes to be laid on concrete slabs or screeds, the substrate should be sufficiently dry to prevent any adverse effects. A 50mm screed is likely to require at least 2 months to become sufficiently dry. A concrete slab requires at least 6 months to become sufficiently dry. Alternatively, it should be tested for moisture content in accordance with BS 8201.

Where specified and where timber battens are used above a dry slab, a continuous vapour control layer should be fixed under the wood flooring, with lapped and taped or sealed joints coincident with supports.

The supporting battens below the vapour control layer should be preservative treated and a dpm should have been provided below the slab.

preservative treated battens

Wood blocks and strips should be conditioned before laying to the appropriate moisture content for the specified period.

(b) services

Underfloor heating, where installed, should be kept on before and during the floor laying.

(c) laying and fixing

PREPARATION OF SCREEDS OR CONCRETE SURFACES

Preparation should be as follows:

  • high spots, nibs and major irregularities should be removed
  • differences in level should be dubbed out.

DIRECTLY APPLIED FINISHES

(wood block and strip flooring)

Wood block and strip flooring should be laid and fixed in accordance with manufacturers' recommendations, using the specified or recommended adhesive as appropriate.

Adhesive should be evenly spread, and blocks laid to the specified pattern, leaving gaps around the perimeter for movement.

INDIRECTLY APPLIED FINISHES

(softwood boarding, wood-based panel products)

  • batten spacing - battens should be at centres appropriate to the floor finish material, and generally in accordance with the following:
Thickness of finish (mm) Maximum batten centres (mm)

Chipboard (type P5)

18/19 450
22 600

Plywood

12 450
16 600

Oriented strand board (type OSB3)

15 450
18-19 600

  • batten fixing to substrate - battens may be shot-fired or fixed with suitable clips.
  • chipboard and oriented strand board fixed to battens
Fixing Length Centres
Flat headed ring shank nails or screws 2½ x board thickness 200mm to 300mm centres around perimeters


400mm to 500mm centres on intermediate supports

or in accordance with manufacturers' recommendations.

  • plywood fixed to battens
Fixing Centres
10 gauge nails or screws 150mm centres around perimeter

300mm centres on intermediate supports

nails/screws at least 10mm from edge of panel

or in accordance with manufacturers' recommendations.

FLOOR COVERINGS LAID ON RESILIENT MATERIALS

Where flooring is to be laid on resilient materials on a separating floor, it is important that edges are isolated from walls and skirtings by a resilient layer.

STRUCTURAL DECKING

Floor boards and decking should be laid and fixed as described in Chapter 6.4 'Timber and concrete upper floors' (Sitework).

(d) protection

All wood flooring should be kept protected until handover of the dwelling. Temporary covering should be building paper or other material, which will withstand traffic from other trades and any dampness caused by plaster droppings or spillage.

STAIRCASE FINISHES

8.3 - S7
Staircase finishes shall be suitable for their intended use
 

Items to be taken into account include:

(a) provision of slip resistant nosings

For communal stairs, eg in escape routes in blocks of flats, non-slip nosings or inserts should be provided where specified, and fixed in accordance with the manufacturer's recommendations.

(b) consistent rise and going

The rise and going should remain uniform after application of the staircase finish. Reference should also be made to Chapter 6.6 'Staircases' (Design and Sitework).