TECHNICAL INFORMATION FOR NATURAL STONE
Disclaimer: The correct installation of stone tiles is as important to choosing the product itself. This following section provides some general information that may be helpful in understanding the installation of tiles. The information in this section is of general application only and may not apply to the unique specifications of your site. We recommend that you always follow the advice of your architect, engineer or specialist installer.
- All substrates that are to be tiled to, whether floor or wall, should always be suitably prepared. They should be level, clean, dry and free of dust, grease and any loose material. New sand and cement screeds, for example, need to cure or dry out for about 1 day per mm of thickness.
- All surfaces must be completely secure without any obvious deflection and capable of carrying the additional load. Correct identification of the substrate is vital to ensure the correct advice. With the increasing use of large format materials on walls, it is imperative to ensure that the substrate has a suitable weight bearing capability to accommodate the desired material. For example, the weight limitation for fixing tiles onto a mechanically prepared and roughened concrete surface is 60kg/m2 whereas gypsum plaster skim has an extremely low weight bearing capability of 20kg/m2 (generally precluding the use of natural stone tiles).
- Prior to fixing tiles, damp of any nature should be rectified. If any doubt exists, an expert should be consulted.
- Stone tiles are packed very tightly into crates and because they are wet at the point of production they may have residue from the various finishing processes employed on them. It is recommended (particularly in the case of pale materials) that they are washed and allowed to dry out completely before installation. They will lighten in colour as they dry.
- Dry tiles are necessary before installation so that any tonal markings you don't like can be placed in less visible areas or used for cuttings. At the point of installation always make sure that stone tiles are mixed to ensure you are satisfied with the overall appearance of the tiles. This will mean opening all the crates before you start and dry laying the material. Dry laying is a very important step in ensuring an installation which meets your approval, particularly in the case of pale limestone, sandstone or marbles which may exhibit a marked degree of colour variation.
- Some materials have very little colour variation and others have more, so in cases where the material is very consistent in colour the above step may not be necessary.
- Minor damage such as edge chipping is often caused in packing or unpacking tiles, and should be expected, it is normal practice for these to be used as cuts during the installation process. Don't unpack tiles and store them on hard or uneven surfaces during the tiling process as this can result in edge chipping.
- Uncalibrated stone tiles need to be graded prior to installation; the thicker tiles will dictate the floor level and should be installed first with thinner tiles being bedded up with an appropriate large format floor adhesive.
- Make sure that you have discussed your requirements fully with your stone fixer so that they are familiar with the product to be fixed and your expectations
- Stone tiles must be solidly bedded; cement or gypsum-based tile adhesives are the most appropriate for this method. Some travertine or large format tiles may have to be 'buttered' with adhesive on the back in order to ensure complete adhesive coverage.
- Tiles should occasionally be lifted during the laying process to ensure that sufficient compaction and full bed adhesion is being achieved.
- Fast setting adhesives are advisable in order that the moisture disperses quickly from the stone. This helps to prevent various reactions (such as efflorescence) that could be caused by the moisture retention in the tile.
- Light materials generally require fixing with white adhesives to prevent possible discolouration should the alkaline mortar bleed into, or react with the minerals within the body of the stone itself, and also to prevent shadowing through to the associated light coloured grout.
- Flexible adhesives, combined with further substrate preparation, are required when the substrate is plywood, existing glazed tiles (floor application only), underfloor and/or undertile heating is present or there is any degree of movement or instability in the substrate.
- Existing expansions joins should be respected and not tiled over.
- Cement based grouts are best for stone tile jointing. Tiles with a textured surface tend to have grout joints of 6-10mm, whereas smoother honed or polished tiles can be jointed at about 3-5mm. Larger format tiles require larger grout joins, 10mm is advisable.
- Grout joints are in place to allow for any movement of tiles and should be a minimum of 3mm, 'butt-joining' tiles is not recommended.
- The width of joint selected should be sufficient to accommodate any variation in tile sizes, so when installing random sized tiles an area should be dry laid first to establish the optimum joint width and joint sizes may vary from 3-10mm across the floor depending on the mixture of tile sizes chosen.
- Do not grout the perimeter joints, it is preferable that these should be finished with a good quality neutral cure silicone sealer after the final seal and not with grout. This will allow for expansion and contraction of the tiles during normal heating and cooling cycles.
- Any grout residue on the surface of the tiles should be wiped off immediately as part of the grouting process. Acid should not be used in removing grout or adhesive residue.
- Some stone tiles may absorb pigments from the cementitious grout, so these materials should have an initial sealant coat after fixing but prior to grouting.
- Heavily pigmented grouts may be subject to efflorescence as the salts which hold in the pigmentation are released as part of the drying process.
- If you have chosen a limestone or marble, ensure that the tiles are well protected to prevent scratching from any debris and dust that will remain present until the site is handed over.
SEALING & MAINTENANCE
- Old stone floors were never sealed and yet they still look beautiful today. Nonetheless, all stone is naturally porous (to varying degrees) and so for contemporary living and to improve the stain resistance of your stone we recommend that it be sealed.
- Different materials and finishes will necessitate different treatments. For honed and antique limestone, travertine and marble use a sealant that absorbs into the body of the stone to quell the porosity. Ideally you should apply some sealer to this type of material after fixing but before grouting, since this will prevent grout residue from adhering to the stone. After grouting, another coat of sealer should be applied.
- Slate is naturally less porous than other stones, so a liquid wax surface sealant is sufficient, while sandstone and schist are more porous (despite being similar in appearance.)
- Honed slate, honed basalt and stones that are highly polished have lower porosity levels and will not absorb much sealer.
- External stone will be subject to staining from natural atmospheric agents and organic matter. There is much debate about whether stone should be sealed externally or left to weather naturally, so ultimately this will come down to personal preference taking into account the type of material (it is worth sealing an off-white limestone over a darker, more rustic sandstone or slate) and the quantity (which will determine the cost).
- Areas exposed to water for intense and prolonged periods will require sealers suited to this purpose.
- Like any surface, stone will require a degree of maintenance. Correctly sealed floors are the key to minimal maintenance.
- Heavily trafficked areas will require more maintenance than other areas. Regular sweeping and vacuum-cleaning together with mopping is advised.
- Abrasive or acidic household detergents should be avoided as they can remove the surface sealant or in extreme cases damage the stone.
- Your stone floor can be buffed, re-polished or re-honed (in addition to being professionally cleaned).