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.

Guide: Tiling On Anhydrite Floor Screed



Fixing tiles to anhydrite or gypsum based surfaces requires checks & 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 & 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 or internal locations where they can become damp, frequently wet or in saturated areas. The low shrinkage properties of this system make it a preferred choice for deep bed floor levelling specifications whereby 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 laitence 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 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 anticipated thermal movement of the screed between the maximum operating temperature and expected lowest temperature of the screed.

Before any tile fixing can begin in addition to ensuring moisture content has been tested & 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. NB. 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.

Guide: Fixing Large Format Tile & Stone


Recommendations given by the Tile Association guide suggest 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:

largeformattilesThis 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 is 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 alternatively there are now 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.