Why did my tiles stop sticking to the adhesive?
Combed adhesive skins over surprisingly fast. A tile pressed into a skinned bed touches the ridges and bonds to almost nothing, and it looks perfectly fine until it comes off.
- Difficulty
- intermediate
- Time
- 20 min
- Read
- 2 min
Short answer
Adhesive has an open time — the window between combing it out and the surface skinning. Past it, the tile sits on a dry film and bonds only in patches. Comb out small areas at a time, touch the ridges to test, and if a finger comes away clean rather than tacky, scrape that bed off and re-comb it.
This is one of the least visible tiling faults, because a tile pressed onto skinned adhesive looks identical to one bedded properly. The failure appears weeks or months later as a hollow-sounding or loose tile, by which point the cause is long forgotten. Warm rooms, absorbent substrates, draughts and slow working all shorten the window.
Step by step
- Understand what open time actually is.It is the period after combing during which the adhesive will still wet the back of a tile and bond to it. It is not the same as pot life, which is how long the mixed adhesive stays usable in the bucket.
- Test the bed with a fingertip before every tile.Touch the top of the ridges. Tacky and transferring to your finger is good. Dry, dull or firm to the touch means it has skinned and will not bond.
- Comb out only what you can tile in a few minutes.The single most effective change. Covering a large area to save time is what causes this, because the far end skins before you reach it.
- Deal with the conditions that shorten it.Heat, direct sun on the wall, underfloor heating left on, a fan heater drying the room, or a draught through an open door all reduce open time considerably.
- Prime a very absorbent substrate.A thirsty background pulls water out of the adhesive from behind and skins it from underneath. GuideHQ has a guide on priming before tiling and on why PVA is the wrong product.
- Scrape off any bed that has skinned and re-comb it.Do not try to revive it by spraying water or re-combing the same material. Take it off, and comb fresh adhesive out.
- Do not re-wet or re-temper adhesive that has stiffened in the bucket.Adding water to adhesive that has begun to go off restores the consistency and not the chemistry. The bond it forms afterwards is unreliable.
- Check your work as you go with a lift-and-look.Every so often, lift a just-placed tile and look at the transfer on its back. Patchy or ridge-only contact means you are past open time.
If it doesn't work
Tiles sound hollow in one area but not others.
Cause: That area was combed early and skinned before the tiles went on. — Fix: Those tiles will need lifting and rebedding. GuideHQ has a guide on hollow-sounding tiles and when they matter.
The tile slides but does not grip.
Cause: The adhesive has gone off in the bucket rather than skinned on the wall. — Fix: Discard it and mix fresh. Do not add water to bring it back.
Questions people ask
How long is open time?
It is stated on the bag and varies widely by product, and the real figure in your room is shorter than the laboratory one. Treat the bag as the maximum and test the bed by touch.
Can I mist the adhesive to keep it open?
No. It restores the appearance rather than the ability to bond, and it dilutes the surface of the bed. Comb smaller areas instead.