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Stone and Porcelain Tiles - Installation Guide

The following notes are offered as general guidelines and are based on the many years experience we have in the industry, they do not however amount to any particular method statement. Every job has its own peculiarities and the most important factor is your floor layer. Fixing stone tiles and laying wood floors requires a degree of skill and knowledge and the work should be done by someone familiar with the task. As a customer you should seek agreement with your contractor as to how the work is to be done and what methods and products are to be used. You need him to take responsibility for the results. If you decide that you are going to do the work yourself, please read this section carefully before proceeding and seek as much professional advice as possible to ensure a good result.

Stone Flooring

A well laid stone floor is a thing of beauty and we hope some of the information below will keep you on track for a great job and many years of service from your new floor.

Before you start

Unload all of your stone and store it in the dry. Stone should always be stacked upright taking care to protect the edges - use softening material e.g. dry timber battens, polystyrene or underlay to place it on.

The tiles should be clean and dry before you start. Laying damp tiles is not a problem in itself but the presence of moisture will affect the colour of the stone. Damp tiles will appear different to dry ones. The tiles may need to be cleaned as it is common for them to be packed wet and in some cases residues from the cutting process will need to be washed off with clean water. Start the work only when all the stone is on site. Mix the stones from different crates to insure the natural variation is evenly distributed across your new floor.

Installing Limestone Tiles

Limestone is a soft stone and limestone tiles can be installed in many parts of the home. Limestone installation is similar to many other stone tiles, but limestone is porous so can be stained during installation.

Make sure you take cate protecting the tiles from absorbing colour when putting them in space.

Substrates -Floors

General

All surfaces onto which you intend to tile should be thoroughly cleaned and primed. Any loose or poorly adhered material should be removed. If the floor is uneven some levelling work may be needed. This is time well spent as it will make laying the floor easier and minimise subsequent use of adhesives. We recommend Mira X plan fibre reinforced levelling compound for price, ease of use and its versatility.

Sand and cement screeds

It is generally advised that this type of screed be allowed to dry before tiling begins. Three weeks for a 50 mm screed, four weeks for 75mm thickness. During this time the screed will also harden and shrink. If the stone is laid prematurely any cracking in the screed, which occurs as part of this process, will crack the stone finish. If you can't wait, Schluter Ditra matting should be used as an uncoupling layer. This excellent product can cope with the evaporating water vapour and will successfully bridge any cracks in the screed - its two-layer construction effectively isolates the stone from any stresses occurring below the matting.

Gypsum or Anhydrite screeds

These screeds are pumped into place in their liquid form and offer advantages in terms of speed of installation, the establishing of more accurate levels and they are much less prone to cracking than sand and cement. There are however some important points to understand.

Drying times are extended and must be observed. Approximately one day is needed per millimetre of thickness for up to 40 mm thickness. Two days drying must be added for every millimetre of thickness above 40 mm. A 60 mm thick screed would therefore take 80 days to dry. Some manufacturers allow for heating the screed at an earlier stage to aid drying but note the heat must be turned off for four days in order to test the moisture content. This test requires specialist equipment and we would recommend you make your builder or his subcontractor responsible for declaring their screed ready for use. Tiling can begin when the moisture level is 0.5% by volume or 2% if you use Ditra matting.

Many Calcium Sulphate screeds produce a thin, loosely bonded sludge on the surface which dries to a crust. These 'laitance' as they are known must be removed to reveal the aggregated material beneath. I have been told by sales reps and have read elsewhere that these laitance are easily removed by use of a stiff brush or abrasive pads on a machine. Please note that in our experience much more aggressive diamond tooling is required. You might want to employ a specialist to ensure this essential work is done correctly - (link to floor preparation group).

To avoid a chemical reaction between the Calcium Sulphate and the cementicious adhesives it is essential that the screed, once dry is carefully primed with two coats of an acrylic primer - Ardex P51 is suitable.

Underfloor heating

Flexible adhesives and grouts are required. Warm water systems should be subjected to the manufacturers recommended cycle of heating and cooling to cure the screed. New floors should normally be laid after this process is complete and providing no cracks have appeared in the screed. If cracking has occurred or if time does not allow for this process then Ditra matting must be used.

We recommend the use of Ditra matting for all installations where underfloor heating is present.

Both electric and water based heating should remain off while the floor is being laid and for 14 days after the installation is complete. The heating should then be controlled to increase only gradually up to a maximum of 28 C surface temperature.

Floorboards, plywood and chipboard

'Timber' boards and sheet materials fixed as suspended floors are liable to movement both under load and in response to changes of heat and humidity. Stone does not cope with this and 'flexible' adhesives can accommodate very little movement. Having said that a good quality adhesive is essential but importantly the subfloor must be made as stable as possible. You should be able to walk normally around a room without spilling water from a glass filled to the brim and placed in the middle of the floor.

We recommend using 12 mm Hardibacker board to increase rigidity if this is required. If minimising subfloor build up is a priority, floorboards can be removed and replaced with 22 mm tongued and grooved ply. Ditra matting should then be fitted.

We do not recommend ever tiling directly onto ply or chipboard - particularly if electric underfloor heating is to be installed as this can shrink the timber and cause cracking in the stone finish.

Provided the floor is first made sufficiently rigid, Ditra matting can be installed to prevent this problem.

Existing tiles

Check that ceramic tiles are firmly bonded- any loose or 'live' tiles should be removed. The tiles should be thoroughly cleaned and degreased, allowed to dry and a resin primer applied such as Ardex P82.

Vinyl tiles, if securely bonded can be treated in the same way as ceramic tiles.

Thermo plastic tiles bedded on bitumen based adhesives are often poorly bonded and may well need to be removed. The residual bitumen will then need to be ground away with diamond tooling available from hire shops.

Period quarry tiles should be treated with caution as these are usually laid on a weak sand and cement base, are therefore poorly bonded, have often been treated with waxes over the years and ought generally to be removed. Tiles which do appear to be soundly bonded should be sanded or ground back to remove surface contamination then resin primed with Ardex P82.

Substrates - Walls

Plywood

Although it can accept a mechanical load of about 30 kg / sq m, plywood is not an ideal background for tiling with stone. Again it is the potential for movement which can cause problems. It is unfortunately quite common to find tiled finishes which have cracks corresponding to the joints in the plywood beneath.

We do not recommend ever tiling onto plywood and suggest 6 mm Hardibacker board is fixed over the plywood background assuming it is stable enough to take the eventual load. The backerboard should be screwed back at 300 mm centres in both directions and at 150 mm centres along the edges of each board. A small gap should be left between each board - these joints should be taped with the correct mesh tape and flushed up with adhesive. A 6 mm joint should be left at junctions between wall and ceiling, abutting walls and wall and floor. These details allow for minor expansion in the tiled finish.

Tile backerboard

There are many backerboards available. They are characterised by being dimensionally stable in relation to temperature and humidity. The cement based boards are heavier and slower to work with than those made from extruded polystyrene and reinforced with a fibre glass mesh. The latter product are however considerably more expensive.

Backerboards should be used when tiles of 15 mm ( approximately 40 kg / sqm ) or more are to be used. Follow the manufacturers guidelines.

Plasterboard

Unfinished plasterboards, if securely fixed and provided the paper side of the product is primed can accept tiles up to 32 kg/sq m - most 10 to 12 mm stones. The joints should be taped with mesh and flushed up with adhesive.

Skimmed plasterboard is not suitable for fixing stone tiles.

Sand and cement render

Newly rendered surfaces should be allowed to fully dry before tiling - this will depend on site conditions and could take up to two weeks. Once cured this surface can take 15 mm tiles ( 40 kg / sq m ) or 50 kg / sq m if a stainless steel EML is used.

Movement joints

Natural stone will expand and contract slightly in response to changes in its environment. Similarly stone finishes can 'reflect' dimensional changes in the substrate onto which they are fitted. For these reasons some allowance for movement must be made. Movement joints are formed by leaving a gap between the top of the fixed tile, through the adhesive base to the substrate. This gap should typically be 6 mm and should be filled with a suitable flexible mastic for use with natural stone. Where movement joints are present in a screed or concrete slab a movement joint should also be observed in the stone finish.

A perimeter movement joint will always be required to 'restraining surfaces' - this would include walls, pillars and cast staircases. The gap required to a perimeter wall would normally be hidden by a skirting board.

For larger areas intermediate movement joints should be set in the floor in addition to perimeter joints. These intermediate joints are required where the distance between perimeter joints is over 10m. Additional intermediate joints should be placed at 8m intervals. If the floor is heated it should be sectioned into bays of no more than 40 sq m with no bay being more then 8m long or wide.

Adhesives

Adhesives should be suitable for the intended application.

We recommend the Larsen grout, which is suitable for all the backgrounds mentioned above.

White rapid setting tile adhesive suitable for natural stone. The manufacturers give a consumption rate of 4-5 sq m per bag. In practice we suggest this is too little. Natural stone will vary slightly in thickness and the backs of the tiles should be 'buttered' to aid adhesion and achieve solid bed fixing. We suggest 3 sq m per bag is more realistic.

Schluter Ditra matting

This excellent product is made up of two layers . Its purpose is to uncouple the stone floor from stresses arising from the subfloor which can otherwise lead to cracking in the tiles. For example - where tiles are laid on electric underfloor heating on a plywood base the heat typically shrinks the ply, the adhesive will not cope with this and the tile will crack. Similarly new screeds, especially heated screeds are prone to cracking and slight curling in the long run, again this often leads to cracking. Ditra matting will prevent this and we strongly recommend its use on all new screeds, all timber subfloors and anywhere where you have subfloors of a mixed composition.

Grouting

We recommend these grouts as we find them to be of a very high quality, easy to use and the colour is consistent. Stones with tumbled edges will need to have joints of 5mm or more nominal width, whilst stones with straight edges can be laid with 3 mm joints as a realistic minimum.

Stone tiles should be slurry grouted rather than 'pointed' as the latter method can encourage a 'picture framing' effect.

Sealing

Cleaning and maintenance

The correct cleaning of a stone floor will, over time enhances its appearance and resistance to dirt. Prior to cleaning, the floor should be swept with a soft broom or vacuumed to remove grit and dust. For routine cleaning the floor should be mopped with a well wrung out flat-bottomed mop using a neutral ph soap dissolved in warm water. Between applications the mop should be rinsed in the sink or another bucket of clean water. We recommend Lithofin Easy care. The floor should not be rinsed after applying the easy care but left to dry naturally.

Periodically a stone floor can be deep cleaned with Lithofin Powerclean.

Two neat coats of wax are applied after installation and once the floor has been sealed with Lithofin stainstop.

Resealing of stone floors in domestic settings is typically required every 5 to 7 years.

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