Natural stone can be specified for a variety of installations, from light domestic use to heavy pedestrian traffic areas such as shopping centres and banking halls. The purchase of natural stone represents a significant investment. So two things are critical - to select the right material for the environment and choose an experienced installer with a demonstrable record of quality work on comparable projects.
INSTALLATION
Many factors influence the choice of how best to install natural stone. Reference should be made to BS 5385: Parts 1 to 5 inclusive and BS 8000: Part 11: section 11.1 and 11.2 for full details.
SUBSTRATE
The choice of fixing method will depend on a variety of factors, but the background or substrate to which the tiles are fixed will be the greatest factor influencing the method adopted.
Concrete Floors - Unless finished with a power float, concrete floors are generally too uneven to accept thin bed adhesives. Therefore the tiles will need to be fixed using a semi dry sand cement bed in a thickness from 25 to 70mm. Alternatively, a thick bed adhesive such as Floorfast 20 may be used. Whilst thick bed adhesives can be used up to 20mm thick, the economical average thickness should be approximately 6mm. It is usually more cost effective to either screed the floor or use a self-levelling compound e.g. Periplan 10, prior to using an adhesive to fix the tiles.
Whichever method is adopted, concrete floors should be left to cure for at least 6 weeks before commencing any fixing. When using light coloured stones, white cement with coarse sharp river washed sand is recommended for all sand and cement beds. For thin bed applications the use of white adhesives is recommended to avoid any discolouration caused by absorption through the pores of the stone.
Screeded Floors - A well screeded floor will generally provide a smooth and flat surface suitable for using Tilefast 6 thin bed adhesive. Designed to be used to a maximum thickness of 6mm, such adhesives should be applied with a notched trowel to ensure a solid bed of around 3mm is achieved overall. As with concrete floors, screeds must cure thoroughly before commencing fixing. A minimum of three weeks is recommended.
Timber Floors - It is always necessary to ensure the structural integrity of a timber floor prior to installation of stone. Guidance is given in BS 5385: Parts 3 and 5. In general the most important consideration is to reduce flex in the floor by using a double layer of boarding rather than one single layer of 20mm. The top board must resist moisture movement so a proprietary tile backer board e.g. Pecidur is recommended. This will allow the use of a thin bed adhesive such as Tilefast 6 Flex to be combed directly onto the backing board. If it is not possible to apply a tile backer board, then specialist adhesives such as Timberflex may be used directly onto the timber floor. However, such adhesives are often dark in colour and may cause some discolouration to lighter coloured stones.
Cement-sand Rendering - This is the preferred background for adhering wall tiles providing the render is sound and has been left to dry for a least 2 weeks. Tiles up to a thickness of 15mm can be adhered to a wall using Tilefast 6 Flex.
Plasterboard - If fixing to unskimmed paperfaced plasterboard, the weight allowance for tiling is 32kg per m2. This then allows 10mm thick stone tiles to be applied using Tilefast 6 Flex.
Gypsum Plaster - Before plastering a wall, the masonry should be left for at least 6 weeks to dry. This is particularly important on concrete and concrete block walls or cement-sand rendering. Once plastered, the wall should then be left for a further 4 weeks to allow the plaster to dry. Due to the risk of loss of adhesion between plaster and background, the maximum weight of tiling it can support is 20kg per m2. Only ceramic tiles are recommended for this substrate.
Source: Kirkstone.com