7.6.2.1 General considerations
The relevant British Standard is BS 6431 EN87 Ceramic Wall and Floor Tiles, which is a comprehensive document in 23 parts. Also relevant is BS 5385 Wall
and Floor Tiling. Part 4 of this Standard is a Code of Practice for Ceramic Tiling and Mosaics in Specific Conditions, Tables 3 and 4 list the suitability of
wall and floor tiles in specific conditions. For tiles continuously immersed (e.g. swimming pools), users are advised to ‘refer to manufacturers to confirm suitability’.
For swimming pools, the tiles should be vitrified extruded tiles with a water absorption not exceeding 3% by mass when measured in accordance with Part 11 of BS 6431 Ceramic Floor and Wall Tiles. This type of tile is frost-proof and can be used for open-air pools. The floor tiles in the shallow end of the pool should have a slip resistant finish; this recommendation also applies to the walkways and wet changing areas and other areas which are frequently washed down and used by bathers with bare feet. There are various finishes which are slip-resistant and the choice is largely a matter of experience and personal preference.
Reference should be made to Section 2.16 for additional information on ceramic tiles.
7.6.2.2 Laying the tiles
The tiles should be laid with joints 3–4 mm wide and fixed with a proprietary cement-based adhesive suitable for continuous immersion, such as Ardex Arduflex 5000 or BAL High polymer modified adhesive.
For greater resistance to sulphate attack and leaching of lime from the cement as a result of a negative Langelier Index, a proprietary epoxy-based adhesive, such as Ardipox WS or BAL Epoxy LV, could be used. The cost of an epoxy-based adhesive is significantly higher than a cement-based one, but may be worth the extra compared with the cost and great inconvenience of closing down a pool for extensive remedial work to the tiling, should the pool water prove more aggressive than originally anticipated. The adhesive should be mixed as directed by the manufacturers. It is emphasised in Section 8.6.1 that the pH of the pool water should be strictly maintained in the range 7.2 to 7.8 for effective water treatment. If the pH falls below 7.0, there is a risk that acid attack on the grouted joints between the tiles will take place (Figure 7.6).
The tiles must be fully bedded, the adhesive being applied to the back of the tiles with a toothed and notched trowel, and the tiles being firmly pressed and tamped into position. The thickness of the bed will depend on the regularity of the substrate to which the tiles are fixed. Thin-bed adhesives should be used when the substrate checked with a 2 m straight edge does not reveal any gaps behind the straightedge which exceed 3 mm in depth. Suitable thick-bed adhesives should be
used when the gaps are between 3 mm and 6 mm. It can be seen that the regularity/ trueness of the substrate is of great importance.
Grouting the tiles should not be carried out earlier than three days after completion of fixing. The grout should be a proprietary product from the same manufacturer as the adhesive and compatible with the adhesive.
Figures 7.7 and 7.8 show pools completed with high-quality ceramic tiles and mosaic.
7.6.2.3 Movement joints
Movement joints should be provided in the tiling at 4.5 m to 5.0 m centres, carried down through the rendering/screed to the structural pool shell. Movement joints are also required at all internal angles and changes of direction, and in the floor, at changes of gradient. Movement joints in the tiling are normally 6 mm wide.
As movement joints in the pool shell must be carried up through the rendering/ screed and tiling, it follows that there must be close co-operation between the tile suppliers, tile layers and pool designer if these basic requirements are to be properly met.
All movement joints must be sealed with a suitable sealant. The relevant British Standard is BS 6213 1982 Selection of Constructional Sealants. According to Table
Figure 7.7 View of leisure centre pool finished with high-quality ceramic mosaic. Courtesy,
Pilkington’s Tiles Ltd.
Figure 7.8 View of part of leisure centre pool and walkway slab finished with high-quality
4, the only material recommended without reservation is a flexible epoxy. Other materials are recommended, subject to reference to the manufacturers for their suitability.
This indicates a fairly wide choice, but Table 2 of BS 6213 suggests that the ‘expected service life’ of the silicone, polysulphide and polyurethane type sealants is about 20 years. The estimated ‘life’ of the flexible epoxy sealants is not given, but it would be reasonable to anticipate an appreciably longer life than 20 years.
The British Standards for polysulphide and silicone based sealants are listed by BSI as obsolete. Reference should be made to Section 2.15.
The provision of movement joints recommended for ceramic tiling is also applicable to ceramic mosaics.
7.6.2.4 Tolerances on finished surface Acceptable tolerances on surface regularity are: 1. 3 mm under a 2 m straightedge;
2. difference in level across joints including movement joints: 1 mm for joints not exceeding 6 mm wide; 2 mm for joints exceeding 6 mm wide.
7.6.2.5 Scum channels and deck level pools
Ceramic scum channels provide better circulation of the pool water than skimmer outlets. They should be securely bedded on the shelf formed in the pool wall. The perimeter channel which are an essential feature of deck level pools should be either glazed ceramic or finished with a smooth, impervious and durable coating such as chlorinated rubber paint (see Section 7.10.4), or epoxy resin. The internal surface of the concrete channel should not be left with the bare concrete as this becomes dirty and almost impossible to keep clean.
With deck level pools, the perimeter channel usually discharges to a balancing tank and it is strongly recommended that the internal surface should also be finished with a suitable coating.
Water circulation is dealt with in Chapter 8.
7.6.3 Mosaic
There are two types of mosaic, ceramic mosaic and glass mosaic, the former being the type mostly used. It is particularly suitable for free-formed pools and pools constructed in sprayed concrete when there is a wide cove at the junction of the walls and floor. The ceramic mosaic are fully vitrified and are
therefore frost proof. The tesserae (pieces of mosaic) can be obtained in a variety of shapes, sizes and colours; standard sizes are 20 mm×20 mm and 25 mm× 25 mm.
The basic recommendations for laying ceramic mosaic are similar to those for ceramic tiles and are covered by BS 5385 Part 4 Code of Practice for Ceramic
Tiling and Mosaic in Specific Conditions.
The experience of the author is that the use of a nylon or other mesh embedded on the back of the mosaic can reduce the bond between the mosaic and the substrate (screed and rendering). It is better if the sheets of mosaic have paper on the face which is removed after laying.
Very attractive patterns can be formed with mosaic as can be seen in Figure 7.8.
For the best results, the work should only be entrusted to experienced firms. 7.7 Walkways and wet changing areas
The recommendations given for screeds and tiling for insitu reinforced concrete pool shells apply to walkways around the pool and wet changing areas and shower rooms.
It is essential that the surface of these areas should be ‘non-slip’, i.e. slip resistant, and when the floor slabs are suspended and use made of the space below, the floors must be completely watertight to the same standard as the roof of a building. See Section 4.12.
The non-slip requirement can be readily met by the provision of slip resistant tiles, but the requirement for complete watertightness requires special attention to design, specification and execution.
The design should be based on the water retaining Code (BS 8007). In view of the serious trouble which has occurred in a number of public pools where these floor areas have not been watertight, it is recommended that a waterproof membrane be incorporated in the floor. An insitu brush or spray applied coating in two coats is recommended. The second coat can be sprinkled with coarse sand to provide a key for the cement—sand screed. Because the key provided is not as good as that obtained by exposure of the coarse aggregate in the concrete slab, the screed should be not less than 30 mm thick and laid in bays not exceeding 3 m in width. The length of the bay is less important than the width as the fine transverse cracks which occur can be readily grouted in before the tiles/mosaic are laid.
The membrane should be carried up walls which are built directly from the slab, and all openings in the slab for pipes and gulleys must be carefully detailed so as to be watertight. If a sheet membrane is used this will completely debond the screed from the base concrete and the screed should be not less than 75 mm thick and should be concrete with 10 mm maximum size coarse aggregate. Such a construction would increase the dead load of the floor.
The floors must be laid to falls to drainage channels which discharge to the drainage system and not to the water circulation system of the pool. A gradient of
1 in 40 (25 mm in 1.00 m) should be adequate to prevent ponding, but for safety reasons (to prevent slipping) a gradient of 1 in 60 (25 mm in 1.50 m) is recommended.