If your question is not answered below, then contact the BAL Technical Advisory Service on 03330 030160 or email info@building-adhesives.com

Q: Should plaster walls be primed before tiling?

If using BAL cement-based powdered adhesives, apply 2 coats of neat BAL Prime APD or BAL Primer or 2 coats of BAL Bond SBR diluted 1:2 with water. If using BAL ready-mixed adhesives, priming is not necessary UNLESS the plaster is very shiny and dusty. If so, brush surface with stiff bristle brush and prime with BAL Prime APD or BAL Primer diluted 1:1 with water or BAL Bond SBR diluted 1:4 with water.

Q: Why have cracks appeared in grout joints?

There are a number of possible reasons:

– Deflection in the substrate

– Moisture expansion in underlying boards that are not water resistant

– Tiles not adequately bonded to substrate

– Grout joints wider than max. recommended width for grout product concerned – resulting in drying shrinkage

– Joints not fully filled, leaving voids underneath grout – so grout not supported.

To increase flexural and (at tile edges) adhesion strength, and reduce water permeability, use BAL Admix GT1 or use a BAL epoxy resin-based grout.

Q: How to tile over heated screed?

See page 15 of the BAL Sitework Guidance literature for base preparation details.

The heated floor should be fully commissioned prior to tiling. Once completed heating should be turned off and BAL Rapid-Mat should be fixed to a clean screed and even surface using BAL Single Part Flexible or BAL Stone & Tile PTB with a mosaic trowel. Once fitted, tiling can commence immediately.

Then fix tiles with a 3-6mm bed of BAL Single Part Flexible, BAL Stone & Tile PTB or BAL Rapidset Flexible. When dry, grout with (min. 3mm joint) BAL Superflex Wide Joint Grout – or BAL Wide Joint Grout with addition of BAL Admix GT1 (diluted 1:2 with water) or BAL Microcolour Wide Joint Grout.

Once the floor is grouted the heating should be left off for two weeks before being turned back on.

Q: How long should cement:sand screed be left before tiling?

Three weeks for Portland cement (including seven days cure and two weeks continuous drying out in air) or 24 hours for screeds incorporating BAL Quickset Cement.

If it is not possible to allow Portland cement:sand screed to dry for 3 weeks, allow min. 24 hours for drying, then tile using BAL Green Screed adhesive unless containing underfloor heating (the commissioning process should be followed as per the manufacturers recommendations).

Q: What is the best tile and grout for travertine tiles?

To avoid discolouration on travertine, limestone or other light-coloured stone, the adhesive should be a white cement-based adhesive. Also, to avoid staining use a rapid setting adhesive. Ideal choices are BAL Rapidset Flexible Adhesive for walls and BAL PTB Flexible or BAL Stone & Tile PTB Adhesive (white) for floors.

Lay tiles with 3-6mm solid bed onto floors. Do NOT spot fix, as this may result in shading. To avoid migration of materials in solution into the travertine stone, use a grout colour similar to that of the tiles. To avoid ”picture-framing’ effect on very porous stone, seal tiles with a suitable sealer. Also reduce the risk by using cement-based grouts containing a water-retaining agent. BAL Superflex Grout, BAL Wide Joint Grout, and BAL Superflex Wide Joint Grout are all suitable for use with natural stone. Alternatively, use a rapid-setting grout such as BAL Microcolour Micromax2 Grout or BAL Micromax2 Microcolour Wide Joint Grout.

Q: Can 600x300mm porcelain tile be fixed to plasterboard wall with ready-mixed adhesive?

Not recommended.

Note: Porcelain tiles have extremely low porosity. Ready-mixed adhesives rely on water loss through the joints, background substrate or tile to achieve full bonding. As the tiles have low porosity and joints are reduced due to the large tile size, ready mix products struggle to set. Instead, prime the plasterboard with neat BAL Prime APD or BAL Primer, and then use highly polymer-modified adhesive such as BAL Single Part Flexible or BAL Rapidset Flexible. These set via a chemical reaction.

Q: Are there weight restrictions when tiling onto plaster?


The maximum weight of tiling per m2 on Gypsum Plaster is 20kg/m2 or 32kg/m2 on Gypsum Plasterboard direct (i.e. without plaster skim) [See page 6 of the BAL Sitework Guidance literature]. As a general rule, remember to allow approx. 2-4kg/m2 for weight of adhesive and grouts in addition to the weight of tiles. For proprietary boards please check with individual board manufacturers for their weight of tiling guidance.

Q: How do I fix ceramic tiles to calcium sulphate / anhydrite-based screed?

See page 12 of the BAL Sitework Guidance literature for base preparation details.

Protect floor against water ingress (moisture content must be <0.5% by weight or 75% relative humidity before tiling may begin. Measure moisture by hair hygrometer 75% RH or CM tester (‘speedy moisture tester’) or oven drying at 40°C.

The floor should then be abraded to remove any surface laitance in accordance with BS 5385 Part 3 Calcium sulfate-based levelling screeds prior to tiling.

Prime first with two coats of BAL Prime APD or BAL Primer. The first coat should be pre-diluted 1:1 by volume with water and allowed to dry followed by and second undiluted coat. Allow to dry before fixing tiles with e.g. BAL Stone & Tile PTB or, if incorporating underfloor heating use BAL Rapid-Mat.

Q: Can timber floors be tiled?

Yes, provided that they are capable of carrying the additional load, and are sufficiently stiff. To provide extra rigidity, noggins should be fitted between joists, as recommended in BS 5385-3. Alternatively, fix exterior grade or marine grade plywood (min. 15mm thick) over existing boards. Check that there is adequate ventilation and a damp-proof course. [See page 13 of the BAL Sitework Guidance literature for base preparation details of timber floors – including those with and without an overlay].

If direct fixing is possible, remove all traces of previous finishes (stain, varnish) before tiling. Lay a solid bed of BAL Single Part Fastflex Adhesive, ideally 3-4mm thick or alternatively install BAL – Rapid-Mat using BAL Rapidset Flexible Fibre or BAL Rapid Flex Fibre Plus. If fixing to an overlaid timber floor, lay a solid bed of BAL Single Part Flexible Adhesive or BAL Rapidset Flexible BAL Rapidset Flexible Fibre or BAL Rapid Flex Fibre Plus adhesive, ensuring NO voids left underneath tiles. 

Q: What's needed when tiling a wet room?

Above all, make sure the walls/floor are suitable for regular wetting.  They should be waterproofed/tanked with BAL WP1 Coating, reinforced with BAL WP1 Polyester Tape/Membrane [See page 17 of the BAL Sitework Guidance literature]. Use adhesives suitable for the tile type and substrate. All BAL dispersion (ready-mixed) and cement-based adhesives are compatible with BAL WP1 Coating. If a power shower is being installed, check that the chosen adhesive is suitable.

Grout: If single-head showers (including power showers), BAL Superflex Grout, BAL Microflex Grout, BAL Superflex Wide Joint Grout and BAL Microflex Wide Joint Grout are suitable. If multi-head shower and body jets, consider using BAL Easypoxy AG Grout.