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Guide: Tiling On Floating Floors


All tile fixing should be carried out in accordance with BS 5385: WALL & FLOOR TILING Part 3 1989 – Code of practice for the design & installation of ceramic floor tiles and mosaics. Section 14.4 of this standard emphasises the need for timber substrates to be more than suitable for carrying the expected load and they be stiffened prior to tiling. Ceramic floor tiling should never be installed on floating timber floors subject to heavy static or dynamic loads.

This latter point emphasises the fact that a timber base alone may allow deflection, which is beyond the tolerance of the ceramic covering to be applied, therefore the need for rigid sheeting and screw-fixing is essential to ensure stability and rigidity.

Floating floors, by definition, are not fixed to the base substrate and so, before tiling a floating floor, it is essential to determine that its structural stability is sufficient to meet the requirements of BS 5385, part 3, section 14.4.

A typical floating floor lies on a concrete base and is characterised by a layer of rigid insulation topped with flooring grade plywood or chipboard (18 – 20mm deep). The insulation layer should be of sufficient density to provide firm support to the overlaid board. Expanded polystyrene is not considered to be a suitable underlayment for a floating floor which is to receive ceramic. To further ensure the rigidity of this structure, the timber board can also be constructed as a raft fixed onto timber battens (45mm x 45mm) with the insulating material laid between them.


To prevent excessive deflection, it is essential that the board is 18mm – 20mm thick and that the insulating material is sufficiently dense and rigid to support the expected load without risk of excessive compression or movement.

Joints between the sections of chipboard should be tongue-and-groove located and bonded with a waterproof wood adhesive. Any dead joints between adjacent boards must be fully supported as butt-jointed edges to prevent deflection between the two.

All timbers used in the construction of the floor must be moisture-stabilised to the conditions expected within the finished location. Expected moisture-stability should be further protected by the installation of an effective damp-proof membrane within the base structure and provide sufficient heat and ventilation to control humidity within the service environment.

Timber surfaces receiving tiles should be clean, dust-free and clear of any surface coatings likely to impede the adhesive from forming an effective bond to the surface. The use of Tiler’s Primer (SBR) is also advised on all worn or porous timbers and composite boards.

The base substrate must also be even, level, stable and with no localised depressions or elevations likely to cause uneven compression of the insulation layer.

Where the above precautions have failed to secure a stable surface, free from deflection and movement, it will be necessary to overlay the existing board with water-resistant plyboard to a minimum 18mm resistant thickness, laid with staggered joints. Also, battens to support the boards should be fixed to the base substrate at 300mm centres and then install the insulating layer and overlaying boards prior to tiling.

N.B. Do not proceed to fix the tiles if, after all preparatory measures have been taken, the floating floor still shows signs of deflection or movement likely to exceed the rigidity required by the ceramic tiles when subject to the anticipated loading.


Use PALACE Super-Flex two-part adhesive laid using a floor-grade notched trowel to achieve a solid adhesive bed of not more than 6mm thickness.


Use PALACE Flexi-Grout for joints from 3mm up to 20mm wide. In grout situations where heavy trafficking is likely to result in more movement, Flexi-Grout mixed with Palaflex additive (pre-diluted 1:1 grout (pre with water)) will provide even greater movement tolerance.

N.B. All polymer-modified grouts should be cleaned from tile surfaces within 1 hour of being applied as they can be extremely difficult to remove when set.


It is essential to ensure that the full perimeter of all floating floors is sealed with a silicone sealant-based movement joint to a minimum of least 6mm width (in accordance with BS 5385: Part 3 – 1989, clause 19 to 23). This requires joints at all perimeters of the tiled area, coincidental with existing structural movement joints in the substrate and across large floor areas at 8 to 10m intervals.

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Guide: How to Grout & Avoid Colour Variations


It should be noted that due to the variety of application & environmental issues likely to influence the curing of a cement-based grout joint, that it is virtually impossible for the dry composition of the pre pre-blended grout powder to produce localised variations or patchiness in the appearance of the applied grout without first having been affected by any one of the patchiness following factors, all of which are beyond the control of the manufacturer.


It is essential to ensure the powder is mixed thoroughly and consistently in a clean vessel with clean water to form a smooth, homogenous and lump-free paste. Additional mixes of grout for larger projects must be produced from the same batch of powder, using an identical water addition, whilst again achieving a fully consistent, smooth lump-free paste. Never excessively add more water than the recommended volume


All joints to be grouted must be of consistent depth and raked clean of any adhesive residue as any contaminant in the open joints will consequently result in irregularities in the depth & consistency of the freshly applied grout. Both of which may result in shade variation.


Immediately after grouting when wiping down to remove the excess mortar from the tile face around the joints, care must be taken not to ‘over-wet’ the freshly compacted joints, as this may affect water content in some joints but not in others, leading to a higher concentration of fine surface laitance and would raise the possibility of a lighter shaded surface appearance in these areas.

Brushing or dry-wiping over a grouted floor joint when the paste has bodied up, but is still not set can disturb the surface finish and open up the texture of the grout to give a coarser and darker shade than when the grout was first laid and finished off with a wet cloth or sponge and any contact with the surface at this point in time must be even and consistent over all areas to ensure the hardened appearance retains an equivalent degree of dryness and surface texture, otherwise shade variations are likely.


When cleaning the completed tiled surface, you must ensure that the materials and cleaning agents used are applied consistently, are not used at excessive concentrations and are rinsed off promptly as soap and detergent residues can accumulate in joints and affect appearance, particularly when exposed to moisture.


The initial set & hardening of a cement-based grout may result in surface salt & lime deposits forming as water evaporates, known as ‘lime bloom’ and happens when excess water is present either in the mix or after washing the grouted surface.

Efflorescence can also be become apparent when water penetration occurs either through the surface of the cement-based material or from sub-floors where no effective and adequate damp proof course is in place. This phenomenon often diminishes over time with repeated surface washing & drying, however control of mixing water dose and also the wash cycles during the removal of grout stain residues will also reduce risk of efflorescence in the cured joints.


Variations in the density or porosity of the surface beneath the tiles will encourage some areas of the grout joints to dry out at a different rate to others, usually illustrated where darker areas of the grout are laid over dense or impermeable section of flooring, whereas lighter shades will be evident over the more porous and drier sections of the substrate flooring.


The end use of the tiled location needs some consideration as this may result in some areas being exposed to wetting more frequently than others, which consequently will result in the damper sections appearing slightly darker than the drier areas. Regular and localised wetting of one area at a more frequent rate than the surrounding tiled area will result in a shade variation due to the moisture level retained within the cured tile joint.


Porous tiles, substrates or joints adjoining the cut edge of a tile will be exposed to greater risk of moisture absorption from the wet paste than less porous surfaces or true tile edges. This can produce localised variations in moisture content and when fully cured will manifest in a shade variation from joint to joint.


To maintain an ideal consistent appearance in all grout joints, it is essential to ensure consistency is applied at all stages of the application process, including the type of tooling used to finish off joints, the amount of moisture introduced & allowed to remain when cleaning the tiled surface and the finish time which elapses between initially compacting the joints and then returning to tool the joints to a smooth clean edged finish. Where any one of the above precautions is not followed then it is possible to encourage shade variation in the final colour of the hardened grout, which may only then resolved with the application of a mildly acidic surface cleaning agent. 

It should be noted that in most cases, the lightening of dark joints is due to efflorescence blooms of naturally occurring lime which is released by drying cycles from within the Portland cement base. This is often a transient feature as the natural cycles of wet & dry periods following cleaning or exposure to weather (if external) will result in the surface stabilising to a consistent shade as the lime is washed away.

A document is also available here for printed reference.

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Guide: Tiling On Timber Floors


All tile fixing should be carried out in accordance with BS 5385: WALL &FLOOR TILING Part 3 1989 – Code of practice for the design & nstallation of ceramic floor tiles and mosaics and the Tile Association guide – “TILING TO TIMBER SHEETS BOARDS & TIMBER SUBSTRATES. Section 14.4 of BS 5385 part 3 1989 emphasises the need for timber substrates to be more than suitable for carrying the expected load and then be stiffened prior to tiling. The moisture content of timber can vary depending on the temper temperature and humidity conditions depending on it’s storage location. To ensure dimensional stability of structural timber it is essential to allow time for the moisture content of the wood to form an equilibrium with the ambient conditions of the environment where it is to be permanently installed. Composite wood boards will stabilise to lower moisture contents than is the case for solid wood structures. Timber should be conditioned to suit its’ intended environment by storage for a suitable period of time until the moisture content stabilises to an acceptable level. The table below indicates the normal “in “in-service” moisture contents for softwood timbers, studwork & battens:
Conditions% moisture in Softwood timbers% moisture is composite boards
Unheated15 – 19%Up to 15%
Periodic heating10 – 14%9 – 12%
Continuous heating9 – 11%7 – 9%
Under-floor heating6 – 8%5 – 7%
Failure to ensure the moisture content of structural timbers is within the ranges shown above could result in dimensional changes which can adversely affect the stability of any bond between it and rigid ceramic or stone tiles.


Tongue & Groove Floorboards should be fixed directly onto joist spaced no joists more than 300mm and should only be tiled over using 2-part Super-Flex adhesive Plywood is available as “wood based panel” or shuttering ply (as defined in BS EN 313-2) however Marine Plywood (BS 1088) is more durable, water 2) resistant and hence suitable for tiling. WBP Plywood (Water & boil proof) is similar to Marine ply but has no BS classification. Particle board (Chipboard) is defined in BS EN 309 and is an adhesive bound agglomeration of wood particles suitable for receiving tiles only in permanently dry areas All of the above types of timber board when used for flooring must be a minimum of 15mm thick and screw fixed over stable battens at no more than 300mm centres to be structurally acceptable for fixing over with ceramic tile adhesives. Multi-Layered Strand board (OSB board) as defined in BS EN 300 are oard) suitable for tiling usually on wall surfaces. They are generally 11mm to 18mm thick, bound with a strong adhesive and incorporate water repellent components to provide improved moisture resistance


WALL TILE FIXING: The use of sheets and boards that are still subject to movement from changes in moisture content should be avoided it at all possible and the exposed backs and edges of boards should be sealed against the ingress of seal moisture to reduce the risk of movement and warping. In general where a sheet or board has a smooth or rough side, the latter should be used as the receiving surface for tiling. Joints between boards should define the position of movement joints and should not be bridged over with tiling. (BS 5385 part 1). Mechanical screw fixings of appropriate dimensions should be used to secure all types of boards to rigidly stable and secure battens, frameworks and noggins. NB. On wall surfaces heavy duty stone tiles should not be fixed to fibreboard or chipboard. FLOOR TILE FIXING: Existing timber bases should be sufficiently strong & rigid before they are to receive tiling and be checked that they are capable of carrying a static load (up to 0.8Kn/m2) and a dynamic load without perceptible deflection. Stiffening the floor with new joists or additional noggins may be required where deflection is detected. Ventilation beneath the timber floor must be provided for by air bricks or similar means. The appropriate grade of board for flooring will be a minimum 15mm thickness of either Marine or WBP plywood (BS5385 part 3) with the exposed back and edges protected from moisture ingress with a water resistant sealer (Tilers primer SBR is acceptable). Counter sunk screw fixings at a minimum 300mm centres should secure the unter boards to joists and noggins where joints between boards should also be coincidental with the support below. Boards in areas where frequent wetting is likely (showers & wet-rooms) should be protected by the application of a waterproof membrane (Palace Shower-tight) or an un-coupling membrane before fixing proceeds


Adhesives should be selected which are recommended for use over timber substrates. On walls D1 or D2 ready mixed dispersion adhesives can be used with selection depending on the degree of exposure to moisture. Cement based adhesives should be classified to BS EN 12004 C2. Palace Multi-Flex, Easi-Flex & Trade-Flex are all suitable for fixing to timber boards on wall & floor elevations. Super-Flex 2-part flexible adhesive should be Flex 2 used on tongue & groove or floating timber floors


Use Palace Flexi Wall & Floor grouts for joints from 3mm up to 12mm wide. Note all polymer modified grouts should be cleaned from tile surfaces within 1 hour of being applied as they can be difficult to remove when set.


It is essential to ensure that where tiling is coincidental with a floor joint or a change in floor surface type that a movement joint is formed with a silicone sealant to a minimum of 6mm width (In accordance with BS 5385: Part 3 -1989, clause 19 to 23). This requires joints at all perimeters of the tiled area, coincidental with existing structural movement joints in the substrate and across large floor areas at 8 to 10m intervals.
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Guide: Waterproofing and Tanking Before Tile Fixing


Many properties have basements, cellars and vaults that were never designed for modern living. They can suffer from rising damp and penetrating damp and even flooding, and as a result are not used to their full  potential. Converting this valuable space into a dry warm living area can greatly enhance property values and help to utilise the full potential of the available space within a building however it must be achieved by eliminating the ingress of damp which penetrates the floor and walls which are all below ground and DPC level. The two most common systems are either the application of a cementitious water-proof slurry coat or the installation of a cavity membrane system, linked to a pump dispersal unit.


is a single-pack blend of special cements; ultra-fine quartz, pore-blocking water repellent crystals and copolymer based adhesion aids, which readily mix with water to form a pourable brush applied slurry. This free-flowing mix readily penetrates the open surface masonry capillaries and engages in a reaction with any available free-lime within the  substrate forming expansive, but insoluble pore blocking micro-crystalline structures, achieving a secure and permanent key within the masonry sufficient to repel and withstand the level of hydrostatic water pressure likely to be exerted in underground structures such as cellars and basements. PALACE DAMPSHIELD has been widely used to provide a permanent barrier against penetrating damp in many application both above and below DPC level such as cellars; retaining walls; lift shafts; swimming pools; vaults; tunnels and has also been used to line water tanks and irrigation channels due to its’ suitability for use in contact with potable water. This type of tanking system provides a cement-based waterproof coating which cures within 24 hours to prevent penetrating damp caused by capillary movement of water moving through earth retaining walls. It can be applied as a slurry coat to well prepared and clean brick-work or masonry forming two layers over the floor and wall, applied by brush or trowel to a depth of about 3 – 4mm. The tanking coatings can then be plastered or rendered over to provide a smooth surface over which a decorative finish can be applied thus completing the conversion of the cellar or basement into a pleasant living or working area. The benefits of cementitious tanking are: • It can be used in small areas and on convoluted surfaces. • Does not require a drainage system or a sump and pump. • Is versatile and relatively easy to apply in confined spaces. • Form a bond with any suitably prepared masonry substrate. • Creates an imperious barrier to the movement of water.


The need for containment of moisture within a wet area as opposed to keeping the problem outside of a damp susceptible room such as a basement or cellar requires an entirely different approach to terproofing. The increasing popularity of walk-in showers and wet rooms allied to the need to comply with stricter regulations with regards to leakage control in multi-floor dwellings raises the need for containment of moisture within a wet area and protecting the surrounding structure from the damaging effects of moisture penetration and ingress. Modern construction methods now allow for showers and wet-rooms to be constructed within rooms and buildings which are built with timber and other similar moisture sensitive structures. Whilst replacing timber and plaster boards with cement panel boards may over-come some of the risk of moisture degradation, in many cases the conversion of a room from a dry use to a wet use requires a more manageable method which takes account of the original materials in the structure. Cement based systems such as DAMPSHIELD are only suitable for application onto prepared bare masonry and the panelled timber walls of most modern properties require an altogether different solution. Liquid  applied waterproof impermeable membranes provide an easy to apply solution to creating a protective barrier between a frequently wet tiled wall and the substrate beneath.


is a waterproof barrier system designed to protect water sensitive structures and surfaces in tiled areas where regular and frequent exposure to damp conditions is expected, such as showers, bathrooms, wet-rooms and kitchen utility areas. This multi-component system consists of a surface primer to ensure good adhesion to the substrate; a grey flexible waterproof coating to prevent the passage of moisture and super strong polyester matting to reinforce seams in joints around wall floor junctions and where piping enters and exits the wet zone. This provides a seamless, durable protective membrane to inhibit the passage of moisture from within the tiled area through to surfaces and structures which may be sensitive to the effects of prolonged water migration, such as plaster, render, plasterboards, tile backer boards, timber, suspended floors and plywood overlays.


waterproof membrane offers a convenient system for the preparation of an area to be tiled ensuring that surrounding substrates and structures remain protected from the risk of any water migration through the subsequently applied tiled surface. The use of waterproof tile adhesives will further guarantee the stability and durabilty of the tiled walls & floors by ensuring that the damaging effect of moisture penetration are revented from causing deterioration to the surrounding wall & floor structure.
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Guide: Tiling On Anhydrite Floor Screed


Fixing tiles to anhydrite or gypsum-based surfaces requires checks and additional preparation measures to be undertaken to avoid the adverse reaction which can often occur between cement-based adhesive mortars and this type of substrate, which invariably results in lifting and failure of the bond if the following action is not undertaken.


Anhydrite screeds are also referred to as calcium sulphate or gypsum-based screeds and are a mix of fine and coarse aggregates with a calcium sulphate (gypsum) binder and therefore look similar to a cement-sand screed. Often, a light colour, almost white, will indicate that the screed is likely to be calcium sulphate based. Other descriptions to identify the screed as anhydrite-based can be made by referring to the flooring contractors’ supplier or manufacturer, where names such as Lafarge GYVLON or Tarmac TRUFLO identify a commonly used source of this type of underlayment. Anhydrite screeds are not suitable as a wearing surface or for external/internal locations where they can become damp, frequently wet or reside in saturated areas. The low shrinkage properties of this system make it a preferred choice for deep-bed floor-levelling specifications where the thickness of an anhydrite screed can be typically in the range of 25mm to 80mm; ideal for embedded sub-floor heating systems.


Before considering fixing tiles to an anhydrite screed, there are several essential preparatory steps to consider: The removal of a loose friable layer of surface laitance must be carried out usually 4-6 days after application using appropriate equipment. This will also assist the drying of the screed. Screed drying time is approximately 1mm/day up to 40 mm thickness under ambient temperatures and drying conditions. This will increase for screeds thicker than 40 mm deep and in poor drying conditions. To ensure optimum surface conditions, it is essential that good drying conditions are provided from the day the screed is laid. When first laid, the screed should be protected from conditions likely to cause very rapid drying and also atmospheric humidity must be low, i.e. not greater than 65% RH, and the air temperature must be adequate (e.g. 20°C). Good ventilation or the use of dehumidifiers can assist in lowering humidity.


Before ceramic floor tiles are laid, the moisture content of the screed should be checked to ensure that it is adequately dry and there are two commonly adopted tests to do this: The British Standard BS8203-1:2001 method for measuring the moisture condition of a screed is to use an electronic meter or hair hygrometer. This non-destructive test method gives a figure which should equate to approximately 75% relative humidity (the required limit for floor finishes). For reliable results, the BS8203 method must be strictly adhered to, including the use of a correctly sized and insulated box sealed to the floor, be given sufficient duration (typically 48-72 hours) and be protected by an impervious sheet around the instrument.

Alternatively, a carbide moisture meter test can be used whereby required values will need to be equivalent to 0.5% water by weight for moisture sensitive floor coverings (e.g. ceramics and adhesives). This figure equates approximately to 75% relative humidity. A typical example is for a screed thickness of 30mm with an ambient temperature of 20°C and with good ventilation that should reach a moisture content of 0.5% in approximately 30 days. Electronic meters may be useful in determining where wetter and drier areas of screed are located, but either one of the above methods should be used to determine whether a screed is actually dry enough to receive the flooring.


The maximum permissible departure from a 2m straight edge resting in contact with the floor should be no more than 3mm. Checks should also be made to ensure that movement joints have been installed in the screed at intervals and positions commensurate with the scale of the installation and also any coincidental joints below the screed. In anhydrite floors where sub-floor heating is to be activated, the width and spacing of movement joints should be sufficient to accommodate the anticipated thermal movement of the screed between the maximum operating temperature and the expected lowest temperature of the screed.

Before any tile fixing can begin, in addition to ensuring moisture content has been tested and verified to comply with the above conditions, the surface of the screed must have been correctly prepared to ensure removal of all laitance and loosely bound particles. Laitance is the loose or weakly cohesive fines present on the surface of a screed and should always be swept and vacuumed by the tiling contractor to remove all dust and friable material such that the surface to be tiled is then clean, dry and sound.


To ensure maximum adhesion, and to avoid an adverse chemical reaction such as expansive ettringite formation between the sulfate in the screed and cement-based adhesives, the screed must be primed with a coating compatible with the tile adhesive and two coats of neat TILERS PRIMER which will provide complete & effective coverage, be absorbed into the calcium sulphate screed and prevent chemical interaction with the cement-based adhesive.

N.B. When fixing tiles to a gypsum wall plaster, the same preparation, priming & sealing procedure will be required.


The recommended adhesive for tiling over primed calcium sulphate screeds is a polymer modified cementitious adhesive having a C2 or C2F classification and the selection will depend on several factors, including, the type of tiles being fixed or If the screed is unheated or heated. Palace Trade-Flex, Multi-Flex or Easi-Flex adhesives are all recommended for fixing over a prepared anhydrite screed and the use of a pourable thick bed adhesive with built-in polymer such as Palace Flexi-Set Thick Bed will be advantageous when fixing large format (600mm x 600mm) floor tiles.

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Guide: Fixing Large Format Tile & Stone


Recommendations given by the Tile Association Guide suggests that the fixer should attempt to achieve “as near as possible 100% contact coverage” of the tile back to the adhesive and in real terms, the average contact area should be no less than 80%. However, on exterior elevations or in shower installations the level of contact coverage should be 95% or more to eliminate any voids beneath the tile where moisture can accumulate.

This level of application consistency can be verified by lifting (shortly after fixing) two or three tiles for inspection, whereby it should be possible to determine that the 80% or 95% coverage is sufficiently distributed to give full support of the tile. Note what happens below when a conventional sized trowel is used to fix various tile sizes, the larger tile on the right sees the contact coverage diminish, even though the same method has been used in each case:

This effect is a common cause of adhesion failure in the medium to long term a the tiled area is subject to persistent loading the lack of full contact achieved with the large format tiles places greate stress on the limited area which remains in contact and is therefore more at risk of delamination when subject to heavier or persistent loading.

The code of practice BS 5385-1:2009 makes the recommendation in section for large format tiles to be “back buttered”, especially where the tile backs have profiles which are buttoned, ridged or deep keyed. A thin coat of adhesive should be spread on the back of the tile before it is then laid on an adhesive bed which ideally has been prepared with either a “large format” 25mm diameter round notched floor trowel or there are new designs of trowel available where the notch design assists in ensuring higher degree of contact coverage. The new euro style trowel/slant notch trowels employ a unique design which places more thin-set mortar onto the substrate and the tile back. The design of the notches allows for easier/faster compaction of the adhesive bed without voids which ultimately leads to better coverage without significantly increasing the bed depth.