Is Tiling Over Tiles Right for Your Bathroom?

Tiling over existing tiles saves the dusty, noisy job of stripping walls back to the substrate, and it can cut days from your project. It only works when the old tiles are sound, well-bonded and reasonably flat. Tap across the wall with a screwdriver handle. A hollow ring means the tile has come away. If you find more than a couple of loose tiles, or the wall feels spongy, remove the lot.

Weight matters. Plastered walls usually take around 20kg per square metre, while plasterboard handles about 32kg. That includes tiles, adhesive and grout. Large porcelain can easily exceed those limits. If the wall is bowed or you want heavy tiles, a tile backer board gives you a flat, stable, waterproof surface that carries far more weight.

Preparing the Old Tiles Properly

Old tiles are often coated in soap scum and limescale, and adhesive will not stick to that. Work through this checklist:

• Remove old silicone from around the bath, shower tray and basin.
• Wash with sugar soap, rinse and let dry.
• Degrease glossy tiles with a specialist cleaner or methylated spirits.
• Key the surface with a diamond abrasive pad. You are creating a scratch pattern, not removing the glaze.
• Vacuum dust, then wipe with a damp sponge.
• Prime with a primer made for tiling over tiles. Do not use PVA, which can soften when wet and cause debonding.

Check flatness. A straight edge should show no more than about 3mm of deviation over 2 metres. If it is worse, backer boards or levelling compound will prevent lippy tiles and uneven grout lines.

Tile Backer Boards: The Reliable Route

Tile backer boards are lightweight, waterproof and designed to be tiled directly. Fix them over sound tiles with flexible cement-based adhesive and mechanical fixings. They come in 6mm, 10mm and 12mm thicknesses. A 6mm board adds little depth, which helps with door frames and tight basins.

Apply adhesive with a notched trowel, then screw through the old tiles into studs or solid wall. Use washers so screw heads do not pull through. Stagger joints like brickwork, then seal every joint and corner with waterproof tape and tanking compound. This creates a continuous waterproof layer, ideal in a shower or around a bath.

Backer boards also suit damaged plaster or textured tiles that would show through. They let you hang heavier tiles than plasterboard alone. The trade-off is extra thickness and cost, but the finish is flatter, stronger and more forgiving.

Choosing the Right Adhesive and Grout

Use a cement-based flexible adhesive, not a ready-mixed tub. Powdered adhesive is stronger, waterproof when set and better suited to bathroom movement. For showers or large areas, choose an S1 or S2 classified adhesive.

• Match your notched trowel to the tile size: 6mm for small ceramics, 10mm or 12mm for large format.
• Back-butter large tiles for full coverage.
• Never dot and dab. Voids lead to cracked tiles and failed grout.
• Use spacers and leave gaps at edges for silicone, not grout.
• Let adhesive cure fully before grouting, usually 24 to 48 hours.

Choose flexible, mould-resistant grout. Epoxy grout is excellent in showers but less forgiving to apply. Seal changes of plane with sanitary silicone rather than grout. Grout cracks where walls meet; silicone moves with them.

Wet Areas, Weight and Ventilation

In a shower, the safest approach is to fit tile backer boards and tank them properly. A tanking membrane or liquid waterproofing creates a continuous barrier behind the tiles. Do not rely on grout and silicone alone. Water finds hairline cracks, and the damage can be expensive.

Keep an eye on weight. A square metre of large porcelain can weigh 20kg or more before adhesive and grout. On plaster or plasterboard, that may push you over the limit. Backer boards solve this because they are fixed mechanically and carry far more. Finally, check your extractor fan. Good ventilation helps everything dry out and keeps mould at bay.

Finishing Details That Make It Last

Fit tile trim around external corners and window reveals, and use a threshold strip at the door. When drilling, use a diamond bit on low speed without hammer action. Hammer action will shatter glazed tiles.

Remove spacers before the adhesive sets hard. Clean grout haze with a damp sponge before it dries. Apply silicone in a smooth bead and tool it neatly. Leave the bathroom to cure for at least 24 hours before using the shower. Keep a few spare tiles for future repairs. With sound preparation and the right materials, over-tiling is not a shortcut. It is a smart, tidy upgrade that transforms a bathroom in a fraction of the time.