Brief guide for the installation of natural stone tiles.
The purpose of this guide is to give information to cover the core principles when installing natural stone tiles on walls and floors. Preparation is extremely important and care must be made to read the various instructions associated with adhesives, grouts and sealants. We advise that for the best results that a professional should be employed to install natural stone. The following guidelines should be read in conjunction with the relevant British Standards including BS 5385 and BS 8000. Please remember once fixed the tiles will not be able to be exchanged or swapped. The following guide is not intended to be complete in every detail but aimed to inform customers and end users of the overriding principles to be used.
Sub floor
The sub floor or substrate refers to the surface to which the tiles will be fixed. The overriding principle is to ensure that the sub floor is solid and will not move after installation. If the sub floor is able to move it is likely to cause cracking in the tiles that are fixed to it. This is called “reflective cracking”.
If planning to tile onto a sand cement screed the screed should be allowed to cure over a period of time. This may vary from days to weeks depending on the screed, the way it was poured and the depth of screed.
If an anhydrite screed has been laid it must be first covered with a barrier of self-levelling compound before tiling. It is not possible to tile directly onto an anhydrite screed.
Timber floors must be made absolutely rigid. Flexible adhesive is NOT an alternative to correctly bracing the floor. Timber floors must be made rigid by covering with 18mm marine grade plywood fixed with screws (not nails) at 8in centres or 6mm backer board fixed with screws (not nails) at 12in centres. This will eliminate as far as possible any movement and hence reduce the risk cracking.
Concrete floors that have been allowed to dry for at least six weeks usually require little other preparation other than applying self-levelling compound to ensure a perfectly level substrate. It is imperative that freshly laid concrete is allowed to dry completely before tiling.
Power floated concrete slabs are very smooth, dense and impervious surfaces and therefore require special treatment to mechanically abrade the surface.
Remember that the level of the sub floor should be set to take into consideration the thickness of the tile, the adhesive and insulation/under floor heating system (if used). If the floor requires levelling using self-levelling compound the datum point should take this into account. Hence the sub floor should be set to allow for all these components before reaching finished floor level.
Fixing to walls
As with floors, walls must also be solid so that there can be no movement of the substrate after installation.
Cement sand renders that have dried for at least two weeks are the preferred surface to receive wall tiles. These materials are traditionally termed renders to distinguish them from gypsum-based plasters, which must be treated very differently.
Concrete walls will almost certainly have been treated with a mould release agent. This must be removed using a high-pressure cleaner prior to tiling.
It is not recommended to tile onto gypsum plaster nor plasterboard as gypsum plaster and plasterboard does not have sufficient mechanical strength. In new construction if it is known that an area is to be tiled it should be left as a sand cement rendered wall and not covered with gypsum.
In general masonry can provide a good background onto which tiles can be applied. If the substrate is not sufficiently rigid walls should be made firm with 12mm backer board fixed with screws (not nails) at 8in centres.
Tiles must never be fitted so as to bridge any damp proof course fitted in a masonry wall, as this would render it ineffective.
For reasons of health and safety the British Standard advises that wall tiles fixed over 3 metres high should be mechanically fixed i.e. screwed, in addition to being secured with adhesive.
Under Floor Heating
Natural stone tiles work very well with under floor heating. It is of utmost importance however that the system is commissioned correctly. All sub floors should be correctly prepared, as described above - including screeds being cured fully.
Under floor heating systems can be electrical or water based. Electrical systems are simpler to install, especially in an existing building. Water based systems are often installed when an entire building is being refloored.
Whichever system is used it is advisable that the heating elements are encased in a layer of self-levelling compound. This provides an excellent heat conductor and also protects the heating system such that if a tile has to be raised for repair or replacement it does not damage the under floor heating system
The under floor heating elements should be firmly fixed to the substrate (stapled or glued in accordance with the manufacturer’s instructions) before pouring on self-levelling compound.
It is advisable to install insulation board onto the sub floor and beneath the under floor heating to avoid heat loss. A suitable 10mm insulation board should be firmly fixed to the substrate with flexible tile adhesive or as advised in the manufacturer’s instructions.
When tiling large areas (over 36 M2) expansion joins must be installed. These isolate any difference in the expansion/contraction of the tiles from the expansion/contraction of the substrate and therefore reduce the risk of the stone tiles from cracking. Expansion joints should be used strategically at doorways of adjoining rooms.
A CORGI or NIECC qualified person should make all necessary final connections for wet and electric under floor systems.
Finally, the under floor heating should never be turned on immediately after tiling. When a suitable length of time has passed the heating should then be turned on slowly using small increments each day until the ideal normal working temperature is reached.
Adhesives, Sealers and Grouts
Adhesives:
There are various adhesives on the market and you should seek professional advice for the most appropriate product in line with the fixing required. Some adhesives are better for floors and others for walls. Adhesives for wet areas in bathrooms often need special attention due to the need to ensure the area stays watertight.
When tiling to walls or floors the objective is to ensure a full bed of adhesive, ensuring 100% contact between tile and substrate. Different adhesives may have different instructions, which must always be obeyed. However, the usual recommendation is to apply a full bed of adhesive to the substrate using a 6mm notched trowel and additionally to “butter” the rear of the tile with a thin layer of adhesive. However, not all tiles and/or adhesives require this process. The adhesive should always be applied in accordance with the manufacturer’s instructions.
Sealents:
All natural stone is porous even stone that is polished and very smooth. All stone must therefore be sealed with a suitable product to ensure it continues to look its best and perform correctly.
Different sealers can also change the look of the stone. Some enhance veins and fissures; some create a more matt appearance and visa versa.
Most sealant manufacturers recommend at least two coats of sealer that should be applied to clean stone, typically once before grouting and once after grouting. The sealant should be allowed to soak into the stone to ensure it protects the stone fully.
It is imperative that the stone is dry before sealing to ensure the stone looks its best. It is also suggested that depending on the “traffic” on the stone, i.e. how much wear and tear it gets that the stone is periodically sealed again every couple of years or so if required.
Grouting:
Grouting should be done after the first coating of sealant is applied. Grouts come in many colours and textures and grout technology has moved forward considerably to ensure that it complements the stone and requires little maintenance after installation.
Before grouting the stone should be clean. Grout joint width and depth can vary considerably depending on the style and look of the stone. Therefore the time that is required to apply the grout and for it to set may vary. Some grouts are specifically designed to be flexible to allow the stone to move in environments where expansion is expected.
It is very important that excess grout is removed after installation to ensure the stone tiles look their best.
Once again professional advice should be sought to ensure the right adhesive sealer and grout are acquired to complement the stone and style of fixing.
Disclaimer
We cannot accept any responsibility for reliance placed on the information included in this guide, neither do we accept any responsibility for the performance of any products referred to in the guide. This does not affect your statutory rights.
Please always use an experienced and qualified installation person for every element of the preparation and ultimate fixing of our natural stone tiles and other products. Please note that refunds and returns cannot be entertained once fixing is undertaken.