This part of BS 5385 gives recommendations for the design and installation of ceramic, natural stone and mosaic wall tiling in normal internal conditions.
It deals with classes and types of background and their suitability to receive tiling using the following fixing methods.
- Bedding in cementitious adhesives on an intermediate substrate or as a direct bedding method.
- Bedding in organic-based adhesive (dispersion or reaction resin) on an intermediate substrate or as a direct bedding method.
- Bedding in cement: sand mortar on rendering or as a direct bedding method.
Terms and definitions
- Bond breaker tape :- self-adhesive tape, usually polyethylene or polytetrafluoroethylene (PTFE) used to prevent sealant sticking to a substrate.
- Natural stone tiles :- Tiles made from rock which has been sorted, dressed or machined to finish.
- Open time :- period of time during which tiles can be adequately bedded after spreading the adhesive.
- Large tile :- Tile that has an edge that exceeds 60 cm combined with a surface area of greater than 1800 cm².
Classification of Tiles
- Ceramic tiles :- Water absorption (E)
- Natural stone tiles :- The thickness of natural stone tiles should not exceed the weight restriction requirements of the different background types (see 22.214.171.124 and 6.4.1). The density of natural stone tiles can vary quite considerably and this should be established at the design stage; they are usually prepared and polished by wet processes and consequently they should be allowed to dry in natural ventilation and be clean before use.
- Mosaics :- The backing material and its adhesive do not occupy more than 25% of the area of each tessera; the critical factor is the spread of the adhesive over the backs of the tesserae.
- Cement :- The cement for cement:sand mortar beds to be used for bedding mosaics should be one of :- a) Portland cement (CEM I) conforming to BS EN 197-1; b) sulfate-resisting cement conforming to BS 4027; or c) calcium aluminate cement (high alumina cement) conforming to BS EN 14647.
- Sand :- For joints of nominal widths of less than 6 mm wide :-
- Plaster :- Plaster backgrounds to receive tiles are usually based on gypsum building plasters and should be in accordance with BS 8481. Gypsum plasters should conform to BS EN 13279-1.
- Water :- Water should be fresh and clean and free of materials deleterious to mortar beds in their fresh and hardened states (see BS EN 1008). NOTE Drinking water is suitable; seawater is not suitable
- Adhesives :- Cementitious adhesives (C), dispersion adhesives (D) and reaction resin adhesives (R) should all conform to BS EN 12004:2007. NOTE For each type it is possible to have different classes, related to the different characteristics. These classes are designated with the following abbreviations. 1: Normal adhesive. 2: Improved adhesive (meets the requirements for additional characteristic). F: Fast setting adhesive. T: Adhesive with reduced slip. E: Adhesive with extended open time.
Backgrounds :- The nature of the background should be established before choosing any intermediate substrate or other preparatory treatment necessary before tiling.
- Porosity and suction :- Porosity and suction affect the adhesion of cement:sand rendering; the amount of wetting required to reduce suction and to ensure uniformity of suction depends upon the nature of the background, the type of mix, the method of application and the ambient conditions.
- Mechanical key :- If a mechanical key is necessary but not afforded by the nature of the background, it should be artificially provided.
- Moisture movement and thermal movement :- Stresses might develop between the background and the tiling system from differential expansion and contraction movements and are potential causes of failure. Where it is suspected that moisture movement or thermal movement of the background and/or tiling threatens the stability of the installation, special precautions or provisions of additional movement joints should be considered.
- Soluble salts in backgrounds :- Soluble sulfates are present in some backgrounds such as brickwork; if these backgrounds become wet, soluble sulfates can migrate into cement-based mortars in sufﬁcient quantities to cause damage from sulfate attack. This type of damage is likely to affect the adhesion of cement:sand renders/beds and cement-based adhesives. Gypsum plaster (calcium sulfate) based materials should not be used as backings for ceramic tiling in wet or damp conditions.
- Staining :- Moisture migrating from bedding mortar or adhesive and from temporally wetted backgrounds can carry soluble materials to the surface of some natural stone tiles and this can result in staining; a trial fixing should be carried out to see if the tiles are affected by moisture from the bedding mortar or adhesive.
Classes and types of background :-
- Dense, strong and smooth materials :- These factors should be given due consideration when choosing the bedding system to use for such backgrounds (which include high density clay bricks or blocks, dense concrete either pre-cast or in situ, some natural stones, glazed bricks and glazed tiles). • Low porosity. • Little suction. • Smooth surfaces that offer no mechanical key. • Drying shrinkage of dense clay bricks or blocks is negligible; in dense concrete, it might vary from low to high according to mix, quality, etc., but is usually no more than moderate, though drying out can be slow.
Application of tiles: methods and materials
- Bedding materials :–Bedding materials that should be used are:
- cementitious adhesives, classiﬁed C as in BS EN 12004:2007
- dispersion adhesives, classiﬁed D as in BS EN 12004:2007
- reaction resin adhesives, classiﬁed R as in BS EN 12004:2007
- Cement: sand mortar
- Setting out :- It is important for the appearance of the finished wall tiling that unsightly cut tiles are avoided and that joints are of a uniform width, true to line, continuous and without steps.
- Movement joints ;- Provision should be made to incorporate movement joints in appropriate positions when setting out the tiling (see 6.5). All joints should be rectangular in section, with firm, straight, smooth edges free from cavities and irregularities. The width:depth ratios and dimensions of the sealant profile in a joint should accord with the recommendations of the sealant manufacturer.
- When forming the joints, it is useful to insert a temporary filler strip that can be removed when the tiling is sufficiently firm; the filler strip can be wrapped in polyethylene film to ensure smooth, clean joint faces and to assist in its removal: care should be taken to avoid grout and other materials becoming trapped in the joint cavity that prevent proper application of the back-up and sealant and might prevent movement of the joint, resulting in damage or displacement.
- Preparation of the tile :- Although tiles should be dry for bedding methods, occasionally, ceramic tiles are fixed in cement:sand mortar and might need to be soaked prior to fixing. The need for soaking should be checked, as neglect of this is almost certain to lead to adhesion failures .
- Mixing of the tile bed materials :- When a proprietary adhesive is used as the tile bed, strict attention should be paid to the manufacturer’s instructions
- Bedding in adhesives – The method to be adopted for fixing tiles varies according to the type of background, the nature of the adhesive and the anticipated conditions to which the installation is subjected in service. which are those usually adopted with this group of adhesives, but there are many products available and some variations in fixing procedures exist.
- Backgrounds :-As per the manufacturer guidance adhesives are suitable for use on mature rendered surfaces, concrete and brickwork, can be used directly onto surfaces such as plaster, wood, metal and glazed surfaces such as existing tiling, unless their adhesive properties have been altered/ improved by the inclusion of polymer additives.
- Preparation of tiles :- Tiles should be fixed dry, they should not be soaked.
- Mixing of the adhesives :- Adhesives should be mixed as recommended by the manufacturer to obtain the desired consistency. The open time of the mix and the working time is defined by the manufacturer and these time limits should be strictly observed.
- Application of adhesive and tiles :- Notched troweling method
- Buttering method
- Tile joints