1. Picking the right tiles
When tiling onto walls, it’s important to think about the surface behind the existing tiles, and whether it will take the additional weight of new ones.
The most common background for tiles is plasterboard, which can hold around 32kg/m². This allows for 3.5kg of adhesive and grout, and 28.5kg of tile. Skimmed plasterboard, on the other hand, can only take around 20kg/m², meaning an allowance of only 16.5kg for tiles after adhesive and grout.
With this in mind, it’s important to take note of the type of tiles that have been used already, their thickness, and the material they’re made of – how much are they likely to weigh? If both the new and the old tiles are relatively heavy, it’s best to remove the existing set before laying the new set.
If the new tiles haven’t yet been chosen, the focus should be on lightweight varieties if the intention is to lay them over the existing set. Particularly in the case of skimmed plasterboard, new tiles will need to be thin, even if the original set isn’t especially thick or heavy.
2. Preparing existing tiles
Before starting, it’s important to ensure the existing tiles are well bonded to the floor/wall. If not, the new tiles could cause the old ones to come loose. This can easily be checked by tapping the old tiles gently with something solid such as a piece of wood. A hollow sound indicates the tile has likely come away from the surface and is not suitable to be tiled over.
If the tiles are suitably fixed to the surface, they can now be prepped for the job. It’s important to check if they’re level before proceeding. If not, a grinder must be used to flatten any areas which stick out from the rest of the surface. If they’ve been sealed, or have a shiny glaze, they’ll need to be roughened with sandpaper to create a key for the adhesive to stick to.
The tiles also need to be very clean, with all dust created from roughening the surface of the tiles removed. Without this vital step, the new set of tiles may simply slide right off. There is no need for priming however.
3. Fixing new tiles
When the surface is ready for tiles, spread a layer of flexible adhesive such as weberset SPF (or weberset rapid SPF) onto the surface of the existing tiles. If the new set of tiles are particularly large or are stud-backed, an additional layer of adhesive on the back of them may be required.
If tiling onto a heated floor, a flexible tile adhesive such as the previously mentioned products is a must to allow for expansion and contraction of the surface beneath the tiles. As quartz isn’t very absorbent, a two-part adhesive that’s extra flexible is required if using this type of tile. Mix weber AD250 with weberset plus (or weberset rapid plus).