Tile Adhesive

In practice

The most common cause of tiling failure is inadequate substrate preparation. Tiles will only bond reliably to surfaces that are: structurally sound (not crumbling or de-bonding plaster); clean and dust-free; and sufficiently stable to not deflect under load. A deflecting timber floor will cause tile adhesive to crack and tiles to de-bond regardless of the adhesive grade used - the floor must be stiffened (additional noggins, thicker deck boards, or a stiffening layer of 18mm moisture-resistant ply over the existing boards) before tiling. Similarly, tiling directly onto existing ceramic tiles is possible only if the existing tiles are all firmly bonded - any loose tiles must be removed, as a tile over a loose tile will fail as soon as the underlying tile moves.

Notch trowel size is critical to adhesive coverage. The trowel notch size must match the tile format: small tiles (up to 100mm) use a 3mm notch; medium tiles (100-300mm) use 6mm; large format (300mm+) use 10-12mm. The trowel is held at 45-60 degrees to produce ridges of the nominal height. When the tile is pressed home and twisted slightly to bed it, the ridges collapse to give full coverage. Coverage can be checked by lifting a just-pressed tile and checking the back - at least 80% of the back face should be covered in adhesive, and 100% in wet areas or for natural stone.