Limestone, sandstone, travertine and all natural stones are products of nature and no two pieces are exactly alike. There will also be small variations in all dimensions. The tiles will arrive in much the same order as they came off the saw, which means that shades of colour and particular markings in the stone are liable to be next to each other. The material should be looked at to establish colour and marking characteristics, and should be “shuffled” before fixing to create a random pattern. Mixing the tiles up will spread these variations naturally over the floor. Any other design details should be agreed before installation.
Stone can be fixed to a suspended floor (with marine plywood or a combination of marine ply and tile backer board) or to a solid concrete sub-floor. Flexible additives to the adhesive and grout are necessary to take up any movement if the stone is being fixed to a suspended wooden floor or over under-floor heating.
The stone is vulnerable until it is fixed, and still vulnerable until it is treated against staining. It may arrive on site wet. This does not prevent it being fixed but it cannot be treated until it is DRY.
Fixing into a screed:
The edges of the tiles will not have been calibrated and are only sawn - a good fixer will "kill" the edges by rubbing each tile with a diamond pad as it is fixed. This 'pass' on all four sides of the tile cleans the edges of the very small chipping from the saw.
White cement should be used as coloured cement may seep through to the face of the stone. Paint the back of the stone with a primer to inhibit any leaching.
The sub-floor should be firm, clean and dry. The recommended depth of screed is at least 35mm for 20mm stone. The mix should be 3 parts washed, sharp sand to 1 part white cement, used semi-dry.
Make sure the stone is clean. Butter the back of the stone with an adhesive slurry before fixing the stone in the screed. In order to stop the stone drying out too quickly, which may result in some tiles not sticking properly, we recommend that the stone is wetted before fixing; alternatively paint the back of the stone with a primer.
Calcium Sulphate or Anhydrite Screeds:
Beware of Calcium Sulphate or Anhydrite Screeds. These are becoming more popular and have several advantages eg. selflevelling, pumpability, good ecological reasons and they work well with underfloor heating. However, normal cementitious adhesives don’t work with these screeds unless the sub-floors are correctly primed. Please refer to adhesive manufacturers advice before fixing any stone to these types of screed. They work well and efficiently if primed and fixed correctly. Ditra matting or other decoupling membranes offer a good solution in these situations.
Using an adhesive:
The stone can be fixed to concrete screed or a suspended plywood sub-floor. However, all floors should be as rigid as possible. Please check this with your builder and/or tiler. Flexible additive should be used in the adhesive and grout especially with suspended floors and those floors with underfloor heating.
Before fixing the tiles ensure that the sub-floor is true and level, free from contamination and loose areas and properly prepared to give a good bond. Ensure that the background to be adhered to is thoroughly dry, solidly bedded, and free from dust and friable matter before starting to tile. Some fixers will paint the sub-floor with a bonding agent.
Make sure the back of the stone is free of dust or similar. Fix tiles with adhesive in accordance with the recommendations of the adhesive manufacturer. Stone tiles, especially in larger sizes, can vary in thickness, so it may be necessary to build up the adhesive to ensure a floor with a minimum of “lipping”. Always start with one of the thicker tiles. Press tiles onto the adhesive and tap firmly into position. It is essential that each tile be laid on a solid bed of adhesive with no voids. If adhesive gets on the face of the tiles clean it off immediately.
Silicon can be used to fix stone to metal supports.
We recommend a gap between tiles of between 2 to 3mm depending on personal preference. We do not recommend that the tiles be butted up, as the size of the tiles will inevitably vary slightly.
Most fixers prefer to apply one coat of impregnator or sealer to the stone before grouting, which acts as a grout release. (Make sure the stone is clean and dry before application of the protection and allow it 24hrs to cure.)
Grout the joints so that they are completely filled. The grout should be pushed in firmly so it goes right into the gaps. We recommend that the face of the stone be completely covered with grout to avoid any possibility of “picture-framing”. Open-faced stones should also be grouted across the face of the tiles in order to fill up any larger holes.
As the work proceeds, thoroughly clean the grout off the surface using damp cloths or sponges. Tool the joints smooth. It is advisable to test a small area of the floor to make sure the grout colour and texture is suitable.
Grouts come in many colours but we would advise pale neutral colours matching the palest element in the stone. Cement, sand and silver sand can also be mixed in various proportions to suit the stone.
These are recommendations, which should not be thought of as definitive. Clifton Stone would like to emphasise that the above mentioned products protect only. They will not make the floor totally impervious to all stains.