Tiling over old bathroom tiles is perfectly legitimate when the conditions are right, and it can save you a messy day of hacking off and re-boarding walls. But it is not a shortcut that suits every bathroom, and in older Edinburgh tenements it often is not the right call. Here is how we decide on real jobs, so you can judge your own bathroom before anyone quotes you.
The existing tiles need to be solidly bonded, flat and dry. If the old surface is sound, tiling over it avoids the noise, dust and skip costs of stripping back, and it protects whatever is behind the tiles, which matters if the original wall is old lath and plaster that would crumble the moment you start chiselling.
The test is simple. Tap across the whole wall with a knuckle or the handle of a screwdriver. A dull, solid sound is good. A hollow ring means the tile or its adhesive has debonded, and anything you fix on top will eventually move with it. As a rough rule, if more than around ten percent of the wall sounds hollow, or any tiles are loose enough to rock, overlaying is a false economy.
If there is any history of leaks, or the grout is black with mould that returns after cleaning, the moisture is usually behind the tiles, not on them. Tiling over that traps the problem where you cannot see it. The same goes for tiles fixed to old painted plaster or plasterboard that has softened, which is common in tenement flats around Leith, Gorgie and Portobello where bathrooms were tiled in the 1980s straight onto whatever was there.
Weight matters too. Standard plasterboard carries roughly 32kg per square metre of tiling, and a layer of old tiles plus adhesive already uses a fair chunk of that. Adding large format porcelain on top can exceed the limit, so heavier new tiles often force the strip-back decision on their own. Shower enclosures are the other red flag: around a shower we would nearly always strip to the substrate and fit a proper tile backer board, because that zone takes the most water and the consequences of a hidden failure are the most expensive.
Preparation is most of the work. The old tiles get degreased thoroughly, because years of soap and shampoo residue will stop any adhesive bonding. Glazed surfaces are then keyed by abrading them, and a suitable primer designed for low porosity surfaces goes on before any adhesive. Loose or hollow tiles come off and the voids are filled flat.
The adhesive itself matters. This job needs a flexible, cement-based adhesive rated for tile-on-tile use, not a ready-mixed tub adhesive, which never cures properly against an impervious surface. New tile edges are planned so joints do not land directly over old joints, trims are fitted where the extra thickness shows at windows and external corners, and silicone rather than grout goes in every internal corner and around the bath or tray.
For a typical Edinburgh bathroom, overlaying usually saves somewhere in the region of £300 to £600 compared with stripping back, once you account for removal labour, skip or uplift costs and re-boarding. It depends heavily on what is behind the old tiles: sound modern plasterboard is cheap to reinstate, while replastering a tenement wall is not, which is exactly when overlaying makes most sense.
Factor in the knock-on details. The extra depth means the toilet, basin pedestal and any shower valve plates may need adjusting, door architraves can end up shy of the new tile line, and electrical accessories on a tiled wall must be extended safely. A quote that ignores these is a quote that will grow later, so ask about them up front.
Yes, if the existing floor tiles are solid and the floor structure can take the extra weight, but the added height often causes problems at the door threshold and with the toilet pan connector. On timber floors, common in Edinburgh flats, we usually prefer to strip back and check the boards first.
Overlaying a typical bathroom takes around two to three days including preparation and grouting. Stripping back usually adds one to two days for removal, waste disposal and making good the walls before tiling can start.
Not if the original tiles were sound and the surface was properly degreased, primed and fixed with the right flexible adhesive. Failures almost always come from skipping preparation or tiling over a wall that was already loose or damp, which is why the initial survey matters more than the tiling itself.