8.2 Wall and ceiling finishes
SCOPE
DESIGN STANDARDS
| 8.2 - D1 | Design standards |
| 8.2 - D2 | Statutory requirements |
| 8.2 - D3 | Plastering |
| 8.2 - D4 | Plasterboard and dry lining |
| 8.2 - D5 | Ceramic wall tiling |
| 8.2 - D6-D7 | Provision of information |
Design that follows the guidance below will be acceptable for wall and ceiling finishes.
Where a fixed shower or showerhead fixing is provided over a bath at a height that will permit persons to stand under, a screen or other suitable means of containing the water should be provided.
Sufaces which will be subjected to water from the use of a showerhead over a bath should be tiled or have an appropriate alternative water resistant finish.
STATUTORY REQUIREMENTS
Designs should be in accordance with relevant Building Regulations and other statutory requirements.
PLASTERING
Items to be taken into account include:
(a) background
Backgrounds should be given appropriate treatment before plastering in accordance with BS 5492 Code of Practice for internal plastering.
HIGH DENSITY CLAY OR CONCRETE BRICKS AND BLOCKS AND DENSE CONCRETE (including floor soffits)
- suitable bonding treatment
- hacking
- spatterdash
- stipple.
MIXED BACKGROUNDS, eg CONCRETE WITH BRICKS/BLOCKS
- may require expanded metal, to provide key for plastering and to reduce the effects of differential movement.
LIGHTWEIGHT CONCRETE BLOCKS
- plaster should not be stronger than recommended by the blockwork manufacturer.
AUTOCLAVED AERATED CONCRETE BLOCKS
- plastering should be carried out in accordance with manufacturers' recommendations, with special care taken regarding the moisture condition of the blocks.
NORMAL CLAY BRICKWORK, CONCRETE BLOCK
- may require raked joints or the use of keyed bricks.
PLASTERBOARD
- reference should be made to BS 5492 for plastering on plasterboard.
(b) services
Services to be concealed by plaster should be tested, where possible, before plastering is commenced (reference should be made to Chapter 8.1 'Internal services' (Sitework)).
(c) plaster mix
Plaster mixes should be specified as appropriate for the:
- strength and surface characteristics of the background
- intended quality of the plaster surface
- application of further finishes.
Undercoats, finishing coats and mix proportions should be as recommended by the plaster manufacturer for the particular conditions of use. Portland cement and gypsum plaster should not be used in the same mix.
(d) plaster thickness
DECORATIVE FINISH
The number of plaster coats should be sufficient to achieve a reasonably plane finish in accordance with the following:
| Surface to be plastered |
Min no of coats |
Thickness of plaster |
| Walls | ||
| Metal lathing | 3 | 13mm (nominal from lathing) |
| Brickwork | 2 | up to 13mm |
| Blockwork | 2 | up to 13mm |
| Plasterboard or concrete |
1 | sufficient to provide a crack-free surface |
| Ceilings | ||
| Concrete | 2 | 10mm (maximum) |
| Plasterboard | 1 | skimcoat |
FIRE RESISTANCE AND SOUND INSULATION
Where plaster is intended to contribute to fire resistance or sound insulation, minimum requirements for plaster thickness are specified in the appropriate statutory regulations.
(e) plastic compound finish
Plastic compound finishes containing asbestos should not be specified.
PLASTERBOARD AND DRY LINING
Dry lining work should be in accordance with BS 8212.
Items to be taken into account include:
(a) support of plasterboard
Supports for plasterboard should be designed so that the following span limits are not exceeded:
| Board thickness (mm) |
Timber support centres (mm) |
Intermediate noggings required |
Perimeter noggings required |
| 9.5 | 400 | No | Yes |
| 450 | Yes | Yes | |
| 12.5 | 400 | No | Yes |
| 450 | No | Yes | |
| 600 | Yes | Yes | |
| 15 | 600 | No | No |
Notes
1. Cut edges should only be used at perimeters. In all other situations cut edges should finish over a support or nogging.
2. Additional intermediate noggings may be required where fire resistance is necessary.
Plasterboard to receive ceramic wall tiling should be supported in accordance with the details given in Appendix 8.2-A.
Where double layers of plasterboard are used, for example for improved sound insulation, board joints should be staggered from one layer to the other and extra noggings provided to support the second layer.
(b) surface facing
Plasterboard should be fixed face side out for both plastering and direct decoration finishes.
Tapered edge boards should be used for surfaces to be decorated directly on the board surface.
(c) fire resistance
Where plasterboard contributes to fire resistance, its thickness and treatment should be as specified in the appropriate statutory regulations.
(d) vapour control layers
Where required to control interstitial condensation, vapour control layers should be incorporated. In timber frame walls, vapour control layers should be in accordance with recommendations detailed in Chapter 6.2 'External timber framed walls' (Design).
In roof constructions, vapour control layers should be in accordance with the following chapters:
7.1 'Flat roofs and balconies' (Design)
(e) fixings
PLASTERBOARD
Plasterboard may be fixed to:
- timber, using plasterboard nails or dry wall screws
- metal, using dry wall screws.
DRY LINING
Dry lining may be fixed by:
- adhesive dabs
- nailing or screwing to timber battens
- screwing to metal channels
- proprietary fixing systems.
Where insulated dry lining is fixed with adhesive dabs, nailable plugs should also be specified in accordance with manufacturers' recommendations.
(f) gap sealing
Gap sealing should be specified, where necessary, to prevent draughts (see Sitework clause 8.2 - S3(f) for details).
(g) coving
Location, type, size and method of fixing should be specified.
CERAMIC WALL TILING
Items to be taken into account include:
(a) background
EVENNESS
Background surfaces for tiling should be sufficiently even to achieve a plane tiled surface.
STRENGTH
Background surfaces should be strong enough to support tiling of the specified thickness.
BOND
The background should provide adequate mechanical key. Very smooth and dense surfaces may require bonding agents for increased adhesion.
UNIFORMITY
Surfaces should be sufficiently uniform to avoid differential movement. Metal lathing or wire netting may be necessary to cover junctions.
SUCTION
Background surfaces should have adequate porosity for the specified method of fixing the tiles. Where cement mortar is to be used as an adhesive, a background containing soluble salts may require special precautions, such as the use of mortar with sulfate-resisting cement.
(b) tile quality
Tiles should be appropriate for their location and intended use. Specification items may include:
- surface finish
- size and thickness
- colour
- edge shape
- fittings (coves, skirtings, etc)
- accessories (soap tray, paper holder, hooks, etc).
The weight of tiles on lightweight plasters should not exceed 20kg/m2 (e.g. not be thicker than 8mm).
(c) fixing
Tiles should be fixed as appropriate for the background, using:
- cement mortar, or
- proprietary adhesive.
Tiles likely to be frequently wetted should be fixed using solid bed fixing method with a water resistant adhesive on a moisture-resistant background.
(d) joint filling
Grouting should be:
- cement-based epoxy resin or a proprietary product
- waterproof in and around shower enclosures where tiling can be saturated.
A sealing method should be specified for the joint between sanitary fittings and adjacent tiling - this is particularly important where movement can take place, eg where timber floors are used.
PROVISION OF INFORMATION
Design information should include:
- schedule of finishes
- plaster thickness, mix and special requirements
- location of vapour checks behind dry lining
- extent and detail of tiled surfaces
- location of services adjacent to tiled surfaces.
Ensure that design and specification information is issued to site supervisors and relevant specialist subcontractors and/or suppliers.
