- 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, and should be expected, 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.
- All backgrounds to be tiled to should be flat, level, clean, dry and free of dust, grease and any loose material.
- Make sure that you have discussed your requirements fully with your stone fixer.
- All stone tiles must be solidly bedded; cement-based tile adhesives are the most appropriate for this method. Some travertine tiles may have to be ‘buttered’ with adhesive on the back in order to fill voids present.
- 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 plywood, 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.
- 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.
- Joints should be a minimum of 3mm to allow for any movement of the tiles, it is not possible to ‘butt-joint’ stone tiles.
- The width of joint selected should be sufficient to accommodate any variation in tile sizes.
- When fixing a mix of sizes such as an opus pattern, the grout gap will vary in thickness due to the layout of the tiles in the pattern.
- ‘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. Most other stones and finishes including Riven, Brushed, 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 either a single part flexible grout should be used or flexible additive should be added to non-flexible grout.
- All stone and terracotta tiles should have an initial sealant coat after fixing but prior to grouting as some tiles may absorb pigments from the cementitious grout.
- Heavily pigmented grouts may be subject to efflorescence as the salts which hold in the pigmentation are released as part of the drying process.
- 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 thoroughly to their respective manufacturer’s recommendations before tiling can begin as they retain moisture for longer periods than conventional sand and cement screeds.
- Generally they should be allowed 1 day per mm thickness of screed up to 40mm and 2 days per mm for any additional thickness over 40mm, however, the screed manufacturers should be contacted for their recommendations.
- Tiling should not commence until the screed has a residual moisture content of less than 0.50%.
- Alternatively Schlüter-DITRA can be used to neutralize the vapour pressure and lay on a screed with a moisture content of 2.0% by volume 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 one - three 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, incorporating the pipes, in accordance with British Standards. After the screed has ‘cured’ it should be heated gradually to manufacturer’s recommendations and then allowed to cool down completely before fixing floor tiles (unless it is an Anhydrite, Hemihydrite or Gypsum Screed).
- 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 5°C per day, up to a maximum temperature of 40°C, 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/Filbre Floor Levelling Compound. This latter method prevents damage to the heating elements during the fixing process.
- Schlüter-DITRA can be installed on to the Floor Levelling Compound/Fibre Floor Levelling Compound 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, so measures should be taken to ensure that the receiving substrate is suitably resistant to moisture and movement in order to prevent deformation and subsequent de-bonding.
- To test a floor for ‘bounce’, fill a glass or bowl completely with water until the ‘meniscus dome’ is apparent on the surface, then walk around the floor 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.
- It may also be necessary to install Schlüter-DITRA which is a 3mm thick uncoupling, anti-fracture membrane which will serve to counter any lateral movement present within the floor. 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 (1 hour approx) 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 from lateral movement at their abutments, it may be necessary to use a movement profile to alleviate any vertical movement; 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 overlaid with a minimum 15mm exterior grade marine ply, treated against moisture absorption and screw fixed at 300mm centres across the board and 150mm centres along the edges to minimise movement. 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 lateral stresses 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.
- Walls: Sand & Cement Render
- This is a good vertical base for fixing stone tiles up to a thickness of 15mm (up to 38kg/m² approx) with a maximum fixing height of 3.6 metres with suitable Wall Tile Adhesive. To accommodate 20mm thick stone (up to 50kg/m² 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 (up to 32kg/m² 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
- There are various construction boards/tile backer boards available, generally they are cementitious, glass-fibre reinforced or extruded polystyrene, and are either water resistant or waterproof. They are available in various thicknesses which will all have a varying weight bearing capabilities. When suitably screw fixed to walls they should provide an approximate load bearing facility of 40 - 50kgs/m², which is generally adequate load bearing substrate for stone tiles up to 15mm in thickness. Individual manufacturers should always be contacted for the relevant information on load-bearing capabilities.
- Walls: Plywood
- 18mm exterior grade WBP plywood can be used and should be sealed on all sides/faces with Priming Agent before being suitably batten fixed with vertical and horizontal wooden supports at 300mm centres and screwed firmly at 150mm centres at all joints and edges, this is generally capable taking up to 30kg/m².
- 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 a proprietary tile backer board, plasterboard or plywood should be suitably primed, where necessary, then screw fixed firmly through to the substrate in order to fix the stone tiles.
- 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 solidly bedded into a semi-dry or dry 4:1 sand/cement mix, dependent on stone thickness.
- Consideration should always be given to the porosity and shade of any stone, for example, a very pale stone should not be laid with a wet mix as pigments from the cement may bleed into the stone.
- 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.
- Waterproofing Membranes & Floor Drains - Wet Rooms
- Any tile which is fitted will not form a waterproof layer, therefore 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.
- Any fall required in a wet room should be incorporated in the substrate where possible.
- 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 plywood 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 from transference of lateral movement.
- 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. It is important when choosing a shower to compare the output of the shower, with the drainage capacity of the drain.
- Showers should not be used for 14 days after grouting.
- 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 40m². 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 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 as well as advice on usage are available from Schlüter Systems.
