Can you tile over plywood? What actually works on a timber floor

The short answer

You can tile over plywood, but not over thin, springy or damp plywood, and never over standard chipboard flooring. The floor has to be stiff enough that it does not deflect under load, dry, clean, and screwed down tight before any adhesive goes near it.

Deflection is the thing that cracks tiles and grout lines, not the tile itself. British Standard BS 5385 asks for a floor that deflects no more than 1/360 of its span under load — in plain terms, a floor you cannot feel move when someone walks across it.

Minimum build-up we work to

On joisted timber floors we want a minimum of 15mm WBP or exterior-grade plywood over the existing boards, screwed at 300mm centres across the whole sheet and 150mm around the perimeter, with joints staggered and a 2-3mm expansion gap left at walls.

18mm is better where joists are at 600mm centres, where the tile is large format, or where a heavy natural stone is going down. Stone is far less forgiving of movement than porcelain.

Existing chipboard or T&G floorboards are not a tiling substrate on their own. Boards move seasonally and chipboard swells irreversibly if it ever gets wet. They get overboarded, not tiled directly.

Plywood versus tile backer board

Cement-based or foam tile backer boards are the better option in bathrooms, wet rooms and kitchens. They do not absorb moisture, they add a decoupling layer, and 6mm board bonded and screwed over an existing sound floor adds very little height.

Plywood is usually the cheaper route on a dry hallway or living space where height matters and the floor is already solid. In a shower or wet room, backer board plus a tanking membrane is the only build-up we will guarantee.

Priming — the step people skip

Bare plywood is porous and will pull the water out of the adhesive before it can cure, leaving a weak, dusty bond. It needs an acrylic primer suited to timber, applied to the manufacturer's dilution and allowed to dry fully.

Use a flexible, S1-classified cement-based adhesive rated for timber substrates, not a ready-mixed tub adhesive. Tub adhesives cure by drying and will not fully set under a large tile, and they have almost no flexibility.

Underfloor heating and decoupling

If electric underfloor heating is going in over ply, an insulation board over the plywood improves warm-up time and gives the mats a stable bed. Always add a decoupling matting layer where the floor is timber and heated — the thermal cycling adds movement on top of the structural movement.

Leave the heating off for at least seven days after tiling, then bring it up gradually over several days. Firing it up early is a common cause of hollow tiles and cracked grout joints.

Movement joints

Perimeter movement joints are not optional on a timber floor. Leave a gap at every wall, threshold and upstand, and fill it with a flexible silicone rather than grout. On larger areas, intermediate movement joints go in roughly every 5m and over any structural joint below.

Grouting hard into a wall is the fastest way to get a line of cracked grout down one edge of an otherwise perfect floor.

When we would say no

Bouncy joists, damp plywood, a floor that has already been tiled and cracked once, or ply laid directly onto old lino or bitumen — all of those get resolved before tiling, or we walk away from the job rather than tile over a known problem.

If you are unsure about your floor, send photos and rough dimensions on WhatsApp and we will tell you honestly what preparation it needs before anyone quotes for tile.