Fixing & Sealing

This section provides stone installation advice. For our full range and prices of fixing and sealing products see the ancillary products section.

The installation and sealing of your stone is equally as important as choosing the stone itself. This section provides only general information on fixing, as it is impossible to provide a single guide due to the variety of factors which need to be considered, when specifying adhesives, grouts, sealants or other specialist ancillary materials.

The information provided should be used in conjunction with a competent stone installer, together with our recommended fixing and sealing products which are carried in stock.

Before Installation

Stones are often packed into crates very tightly, are wet at the point of production and may have residue from the various finishing processes employed. Therefore it is recommended that tiles are washed, either with clean water or a dilution of FilaCleaner and are allowed to dry completely before installation. They will often lighten in colour as they dry.

Dry tiles are necessary prior to installation as any unusual tonal markings can be placed in less visible areas or used in cuts. At the point of installation always ensure batches of stone are mixed to ensure consistency in distribution of any such variation. This will mean opening all crates or pallets of materials supplied.

Minor damage such as edge chipping is often caused in packing or unpacking tiles but it is deemed normal practice for these to be used as cuts during the installation process.

Uncalibrated 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.

Dimensions listed are nominal as slight variation in size and thickness can occur with most stones.

Adhesive

All stone tiles must be solidly bedded; cement-based tile adhesives are the most appropriate for this method.

Fast setting adhesives are advisable in order that the moisture disperses quickly from the stone or terracotta. This helps to prevent various reactions that could be caused by the moisture retention of the tile.

Light stones 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.

Flexible adhesives are required when the substrate is a timber derivative, existing glazed tiles (floor application only), under floor and/or under tile heating is present or there is any degree of movement or instability in the substrate.

For uncalibrated tiles, the appropriate Large Format Flexible Floor Adhesive should be used.

Adhesive Selector (PDF)

Grout

Cement based grouts are most appropriate for stone jointing. Stones with a textured surface tend to have grout joints of 6-10mm, whereas smoother honed and polished stones can be jointed at about 3-5mm.

'Slurry' grouting with the appropriate colour of Wall & Floor Grout is necessary with unfilled travertine and some limestone in order to fill naturally occurring pits and crevices. Polished and Honed materials should however be pointed in order to avoid grout residue being left on the surface of the tile.

Where there is necessity for flexibility in the adhesive then flexible additive must be added to the grout.

All stone and terracotta tiles should have an initial sealant coat prior to grouting as some tiles may absorb pigments from the cement grout.

Interior Substrates

Floors: Sand & Cement Screed

A dry level screed is an ideal fixing substrate. New screeds usually need to cure or dry out at a minimum of 1 week for every 25mm of screed depth.

Schlüter-DITRA is an uncoupling membrane which can be installed on a drying screed as it allows moisture in the substrate to evaporate through its air channels, thus neutralising vapour pressure and bridging any cracks that will occur through the natural drying out process.

Uneven floors can be overcome to a certain extent with Floor Levelling Compound, or alternatively Large Format Flexible Floor Adhesive can be used to fix tiles up to a maximum bed thickness of 25mm.

Floors: Anhydrite & Hemihydrite/Gypsum Screed

These must be cured to their respective manufacturers recommendations before tiling can begin as they retain moisture for longer periods than conventional sand and cement screeds, fixing should not commence until the screed has a residual moisture content of less than 0.50%. Alternatively Schlüter-DITRA can be used to neutralise the vapour pressure and lay on a screed with a moisture content of 2.0% or less.

Any fine laitance which may be left on the surface of the screed should be removed, and the surface of the screed may need to be abraded in order for the adhesive to key in. The surface of the screed should then be sealed with two coats of Priming Agent prior to fixing of tiles.

Floors: Underfloor Heated Screed

This is usually a water piped system which is installed in a minimum screed depth of 65mm, above the pipes, in accordance with British Standards. After the screed has cured it should be heated gradually to manufacturers recommendations and then allowed to cool down completely before fixing floor tiles. If the screed cannot be heated prior to tiling or the screed has developed stress cracks, Schlüter-DITRA should be used over the whole floor area to bridge potential or existing screed cracks to eliminate transference to the tiled floor covering.

After fixing tiles, leave heating switched off for at least 14 days before bringing the floor to a gradual operating temperature at a maximum rate of 58C per day, up to a maximum temperature of 408C, although your underfloor heating supplier will be able to offer more specific advice.

Floors: Undertile Heating

This is usually an electric mat or cable system and can be tiled directly over with suitable Large Format Flex Floor adhesive. Alternatively prior to tiling the electric mat can be bedded into a Floor Levelling Compound. This latter method prevents damage to the heating elements during the laying process.

Schlüter-DITRA can be installed above the mat to effectively isolate the tile covering from the heated substrate, thus preventing stresses from damaging the tile surface. Schlüter-DITRA will not inhibit heat transfer or reduce the efficiency of the heating system.

Floors: Timber

Wood or its man-made derivatives (chipboard/plywood/T&G/floating timber floors) will be subject to movement under load, temperature and humidity. Rigid tiles cannot absorb deflection or compression and will break or de-bond away from their substrate. It should be ensured that the receiving substrate is suitably resistant to moisture in order to prevent deformation and subsequent de-bonding.

To test a floor for bounce, fill a glass completely with water until the meniscus dome is apparent on the surface, then walk around the glass and check for spillages.

If spillages occur then remedial action needs to be taken. Install an overlay of 18mm exterior grade WBP plywood, suitably sealed on the back, face and edges with neat Priming Agent. Cross joints should be staggered, and a gap of 0.5 - 1mm should be allowed between sheets. Boards should be fixed with countersunk screws at 300mm centres in both directions and 150mm centres along the board edges.

Alternatively, or as well as, install 3mm Schlüter-DITRA which is an uncoupling, anti-fracture membrane. This should be fixed with flexible tile adhesive using a 3-4mm notched trowel and thereafter a maximum of a 10mm flexible adhesive bed is applied over the mat to embed the tiles.

Floors: Existing Tiles

Any loose tiles should be removed and the floor degreased and thoroughly cleaned prior to fixing.

Vinyl tiles will require sealing with Priming Agent prior to fixing with suitable adhesives.

Glazed tiles require a slurry bonding coat (made up of 2 parts any adhesive or Floor Levelling Compound to 1 part Priming Agent), to provide a key for fixing with Rapid Flex Wall & Floor or Large Format Flex Floor Adhesive. This coat can be brushed on to the existing tiles and allowed to dry before fixing.

Unglazed tiles or natural stone can be adhered to with any suitable adhesive without remedial action.

Floors: Problematic Substrates

Schlüter-DITRA is a polyethylene membrane with a 3mm thick grid structure and is designed to act as an uncoupling layer for problematic substrates. Differing floor substrates can be overlaid with this matting to eliminate stress cracks at their abutments; it can also be used to bridge screed cracks.

All types of wood or boarded floors are particularly affected by moisture and flex. These floors should be treated against moisture absorption and firmly fixed to its substrate by placing screws at appropriate close intervals to minimise flexibility. Schlüter-DITRA serves as a waterproof membrane and as a vapour pressure equalisation layer to accommodate moisture occurring at the underside. It also uncouples the floor covering from the substrate and prevents the transfer of stresses or flex to the tiled surface.

Un-cured mortar screeds, heated screeds, floating screeds and Gypsum screeds can be subject to deformation due to residual moisture, shrinkage, load stresses or temperature changes. Using Schlüter-DITRA and providing the substrate is sufficiently load bearing, the tile covering can be installed immediately. h. Walls ñ Sand & Cement Render

This is a good vertical base for fixing stone tiles up to a thickness of 15mm (>38kg/m2 approx) with a maximum fixing height of 3.6 metres with suitable Wall Tile Adhesive. To accommodate 20mm thick stone (>50kg/m= approx) the render must be reinforced with stainless steel EML or similar. New renders need a minimum of two weeks to dry out.

Walls: Plasterboard

Plasterboard that has not been skim coated with a finish coat of plaster will take most 10 and 12mm stones (>32kg/m= approx). In these cases the paper face of the board should be sealed with a coat of Priming Agent mixed 1:4 parts water and allowed to dry, the tiles can then be fixed with a suitable Wall Tile Adhesive.

Walls: Backerboard

Hardibacker is a cement based, water resistant tile backing board. This is available in a 6mm or 12mm thickness and when suitably screw fixed, provides a load bearing facility of >35kgs/m=, which is generally an adequate load bearing substrate for stone tiles up to 15mm in thickness.

Walls: Plywood

18mm exterior grade WBP plywood can be used and should be sealed on all sides/faces with Primimg Agent before being suitably batten fixed with vertical and horizontal wooden supports at 300mm centres and screwed firmly at all joints and edges.

Wall: Existing Tiles/Gypsum Plaster Skim

These are not deemed suitable substrates as they do not have the weight bearing capacity required for stone tiles.

If the underlying substrate is capable of supporting the installed load then Hardibacker, plasterboard or plywood should be suitably primed, where necessary, then screw fixed to apply the stone tiles.

Exterior Substrates

Ground preparation for Stone Flagstones or Cobbles depends upon the intended use of the paved area and the site conditions.

Care must be taken to pave or cobble at least 150mm below the damp-proof course of a building and a gradient of 1:60 is necessary to provide a fall to drain water away from a building.

A stabilising layer of at least 100mm of scalping/crushed hardcore must be installed, thereafter a 30-40mm sand bed should be compressed with a vibrating plate compactor. The perimeter tiles should then be bedded in a wet mortar in order to anchor the tiles and prevent spread. The remaining tiles can then be laid in a semi-dry or dry 4:1 sand/cement mix, dependent on stone thickness.

The correctly prepared substrate will support all exterior stone tiles, immaterial of their thickness.

The above information is for tiles of 30mm or over, thinner tiles can be laid externally although they will have to be laid on a concrete slab with adhesive, as per internal applications.

Additional Considerations

Waterproofing Membranes & Floor Drains - Wet Rooms

All tiled areas that will be subject to any amount of water ingress, such as shower enclosures or wet rooms, should have a waterproof substrate prior to fixing, to prevent damage from moisture. This process is called tanking and can be achieved with Schlüter membranes, sealant adhesives and drainage systems.

If choosing a stone shower tray, due to the porous nature of stone, the area will need to be treated as a wet room scenario.

Schlüter-KERDI is a waterproof membrane made of soft polyethylene, which has been covered in a special fleece to anchor the membrane to the tile adhesive. This membrane can be fixed to any even, load bearing, nonflexible substrate with a thin bed of adhesive. In order to maintain a watertight seal the edges should be over-lapped by 50mm. These joints must be sealed with an application of Schlüter-KERDI-COLL to form a complete watertight seal.

Schlüter-DITRA is a waterproof polyethylene membrane with a grid cavity structure and an anchoring fleece on its underside. It can be adhered to the underlying substrate using a thin bed of adhesive. If a waterproof seal is required, the joints should be overlaid with Schlüter-KERDI-KEBA, and sealed with Schlüter-KERDI-COLL. When using Schlüter-DITRA the tile dimensions should be a minimum of 50x50mm, and the adhesive bed a maximum of 10mm thick.

Schlüter-DITRA is flexible and serves a dual purpose for wood derivative substrates, firstly as a waterproofing membrane, when the mat joints have been sealed with Schlüter-KERDI-KEBA and Schlüter-KERDI-COLL, secondly as an uncoupling or separating membrane between the floor and the tiled surface above to prevent stress cracks.

Schlüter-KERDI-DRAIN is a floor drainage system, which when combined with Schlüter waterproofing materials can provide a complete wet room solution. Floor drains with either 150x150mm or 100x100mm stainless steel grates are available.

Movement Joints in Floors

Structural movement joints in the flooring and bed must be sited directly over and be continuous with any structural joints in the base structure.

Perimeter movement joints are necessary where the flooring abuts restraining surfaces, such as perimeter walls, columns, kerbs, steps etc. These joints should be installed unless the distance between restraining surfaces is less than 2 metres.

Intermediate movement joint requirements depend on the dimensions of the floor. In floors with less than 10 metres between perimeter joints, generally no intermediate movement joints are necessary, however they are required to divide larger areas, and these are normally placed at not more than 10 metres apart. Ideally, the distance between all joints (intermediate and perimeter) should be equal, unless other features of the installation dictate otherwise. Over potentially flexible type substrates and underfloor heating, areas without movement joints should not exceed 40 square metres. Additionally movement joints should be placed directly over supporting walls or beams.

Schlüter-Systems are able to offer bespoke specifications for movement profiles. Please find their contact details at the end of this technical section.

Movement Joints in Walls

All existing movement joints in the base substrate must be carried through to the finished surface with a surface movement joint positioned directly over background or plane changes within the substrate.

Intermediate movement joints should be placed vertically at 4 metre centres and at internal corners and columns, etc.

Horizontal movement joints should be positioned at floor and ceiling positions.

A wide range of movement and control joint profiles are available from Schlüter Systems.

Sealing of Stone & Terracotta

It is worth noting that old stone floors were never sealed and yet still look beautiful today. All stone is naturally porous to varying degrees. For modern-day living and in order to improve stain resistance, we would advise for your stone to be sealed.

A vast majority of our sealants are selected from Filas professional range and we work closely with Fila in order to maintain high standards of technical knowledge and support. Fila are recognized as a leader in their field with over 60 years of experience and we are justifiably proud of our relationship with them. The guidelines below are general, and there are exceptions to the rules, both in terms of materials and application. Our highly trained staff will be able to offer you a tailor-made quotation based on your individual requirements. All sealants discussed require varying drying times in between coats.

Honed & Antique Limestone , Travertine & Marble

This encompasses the majority of our stones and they require a base sealant that absorbs into the body of the stone to quell the porosity. FilaFob is our most commonly used base sealant and protects against both water and oil based stains. After the stone has been fixed, and ensuring it is both clean and dry, one coat should be applied with a brush or sponge before the stone is grouted. Applying FilaFob before grouting helps to prevent grout residues adhering to the surface and grout pigments absorbing into the stone.

After grouting, a further one or two applications of FilaFob should be applied to further protect the stone. Any sealant residues must be cleaned off the tile surface immediately as they may leave surface streaking. More porous stones may take several more coats. The grout joints should also be sealed at this time. Once the base sealing process has been completed, the stone should be sealed with a liquid wax surface sealant. This forms a protective layer, making it easier to clean daily dirt and grime from the stone. Two coats are required; the initial application being allowed to dry before the second is applied. You can choose between a matt (FilaMatt), satin (FilaSatin) or gloss (FilaLongLife) finish, FilaSatin being the most popular.

Riven Slate

Slate is naturally less porous, so a liquid wax surface sealant is sufficient for protection. These sealants are resistant to wear and tear and also highly dirt and dust repellent. One coat of either, FilaMatt, FilaSatin or FilaLongLife should be applied after installation but before grouting and then a further coat after grouting, ensuring the tiles are free from any grout residues.

Sandstone & Schist

Whilst these are similar in appearance to slate, they are actually much more porous. The Schist requires coats of FilaFob and then a wax surface sealant. Sandstone is exceptionally porous and may take several coats of FilaFob before it reaches saturation point. Sandstone also has a coarse surface texture and so requires the higher protection of FilaLongLife.

Honed Slate, Basalt & Polished Stones

These stones have lower porosity levels and so will not absorb much sealant. Therefore they only require a penetrating surface seal of Fila MP/90. One or two coats should be applied, before and after grouting. After 24 hours the residue should be removed with a cloth or single-disc cleaner fitted with the appropriate disc. FilaClassic should be used as an on-going maintenance product to replenish the surface seal.

Terracotta

Terracotta generally requires the most sealing of all our products. All Terracotta tiles are raw, porous biscuits that need total impregnation, surface waxing and a finishing coat of sealant. It is worth noting that, due to the nature of Terracotta, salts and minerals present within the tiles may rise to the surface during the fixing process. It may be necessary for this efflorescence to be removed with a diluted application of Deterdek.

The fixed Terracotta tiles need to be clean and dry prior to their initial coat of a 50/50 mix of Boiled Linseed Oil and White Spirit which is to be applied with a clean flat brush. The amount of coats required will vary depending on the type of Terracotta and also position in the firing kiln. Applications should continue until the tiles become completely saturated. Any surplus unabsorbed fluid must be wiped from the tile surface with White Spirit as staining can occur if the residue dries on the tile.

The Terracotta tiles are then grouted ensuring any grout residues are cleaned from the tile surfaces. Once the floor is clean and the grout has thoroughly dried, one or more coats of Fila Naturwax Neutral or Fila Naturwax Brown can be applied to the floor using a cloth and then hand or machine buffed to give a polished shine, if required. To maintain this appearance, apply two coats of a liquid wax surface sealant either FilaClassic, FilaSatin, FilaMatt or FilaLongLife.

Wet rooms, Wet Areas & Stone Bathware

Such areas are exposed to more intense and prolonged periods of water. We would therefore advise more specific water protection involving one application of Fila Hydrorep followed by one to two applications of FilaFob.

External Stone

These areas will be subject to staining from natural atmospheric agents and organic matter. There is much debate upon whether stone should be sealed externally or left to weather naturally. The two primary considerations are quantity and type; sealing large external areas can prove fairly costly. It is worth sealing an off-white limestone over a more rustic/darker sandstone or slate.

External sealing of stone is generally one coat of Fila Hydrorep followed by one to two coats of FilaFob.

Maintenance

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. Any abrasive household detergents should be avoided as they can remove the surface sealant. FilaCleaner is a neutral routine cleaner formulated to work in conjunction with Filas extensive range of sealants. FilaCleaner should be diluted to use as an everyday cleaner, whereas Fila PS/87 is a more concentrated detergent for stain removal in its undiluted state, or diluted for more routine cleaning.

Liquid wax surface sealants such as FilaSatin, FilaMatt, FilaLongLife and FilaClassic should also be used as part of the ongoing maintenance regime. Once a month, add a glass full to a bucket of water and mop over. This helps to refresh the protective surface seal.

Incorrectly applied impregnators, sealants and staining problems all have their antidotes. Please refer to the Ancillary Product Price List for more information.