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Tiling onto plywood

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Under British Standards BS 5385 Part 1, plywood is not a suitable substrate for the direct fixing of wall tiles, therefore when tiling onto walls, a tile backer board is required. However, tiling onto plywood overlaid floors is acceptable under British Standards. For the best results please follow these instructions.
How to assess your floor
It is essential that the existing timber floor is stable, clean and in good condition with adequate ventilation beneath to prevent atmospheric moisture distortion. It should be sufficiently rigid and stable, as any unsupported movement in the subfloor can cause tiles to crack, and the floor should be able to support the additional weight without any deflection (bounce in the floor).

To check whether there is any deflection in the floor, fill a container to the rim with water and place it in the centre of the floor. Standing approximately 1 metre from the container, jump up and down on the floor and if water spills from the container this would indicate there is deflection in the floor which should be corrected prior to the fixing of tiles.

Timber floors that require strengthening ready for tiling can be overlaid using a suitable, flooring grade, 15-18mm thickness WBP plywood or alternatively a suitable tile backer board. Where floors require further strengthening, you may wish to fit additional noggins within the joists beneath the subfloor or floor boards.

Please Note, Plywood should be used as an overlay ONLY and not fixed directly to floor joists.

How to prepare your plywood floor
Flooring grade, 15-18mm plywood should be fixed to the existing subfloor in a brick bond or staggered fashion so the joints are not uniform, screwed down at 300mm centres, ensuring the screw heads are flush with the boards surface. Leave a 2-3mm ‘expansion’ gap around the perimeter of the room to allow for any movement. This expansion gap should be filled with a silicone sealant to prevent it from being filled with tile adhesive when fixing your tiles.

Before fixing your plywood overlay, ensure the reverse and edges of the boards have been sealed using BAL Bond SBR neat, as this reduces water permeability.

It is NOT recommended to use plywood in wet areas because excess water / moisture can cause the boards to over expand, and so a suitable tile backer board should be used with a suitable waterproofing system, like BAL's Waterproof 1C 5ltr.
How to tile onto a plywood floor
When tiling onto plywood overlaid timber we recommend using a flexible adhesive (S1) such as BAL Rapid-Flex Fibre Plus or BAL Flex Fibre Plus . For a sustainable and more eco-friendly option, Regenr8 is a great adhesive available in S1 rapid and standard setting bags of 20KG (white and grey). When using larger format tiles, a suitable S1 BAL PTB (Pourable Thick Bed) adhesive should be used.
How to tile onto a tongue and groove floorboard
If you’re tiling directly onto a tongue and groove floorboard, you must ensure the boards are securely fixed and rigid. Floorboards will need to be primed using two neat coats of BAL Primer APD, best practice is to apply the second coat 90° to the first coat, allowing it to dry between coats. Then apply a highly flexible tile adhesive (S2) such as BAL Single Part Fastflex.
How to grout a plywood floor
When grouting tiles laid over timber you should make the same considerations when choosing your grout as you do when choosing adhesive. That is to say, consider the need for flexibility to cope with the additional movement faced when tiling onto timber.

We would recommend a product like BAL Micromax3 which has extra flexibility that can compensate for the lateral movement. Alternatively, if you’re worried about any movement then use BAL Single Part Fast-Flex adhesive along with BAL Micromax3 grout with BAL Admix GT1 pre-diluted 1:2 by volume with water to avoid any potential issues.

Complete the job by sealing the perimeter movement joints with BAL Micromax3 Silicone sealant, which can be colour matched to the BAL Micromax3 grout.

Floor TilesTiling onto plywood