Can I tile straight onto plasterboard in a shower?
What plasterboard can and cannot carry in a wet area, the boards that are suitable, and the weight limits that decide the answer.
- Difficulty
- intermediate
- Time
- 30 min
- Read
- 3 min
Short answer
Not without tanking it first, and preferably not at all. Standard plasterboard softens when wet and will eventually let the tiles go. In a shower, use a cement or foam backer board, or at minimum use moisture-resistant board with a full tanking membrane over it. Also check the weight — plasterboard on studs has a real tile weight limit.
The question is really two questions: will the board survive being wet, and will it hold the weight. Standard plasterboard fails on the first, and even the good boards have limits on the second.
Step by step
- Identify what is on the wall now.Grey or green-faced board is moisture resistant; ivory-faced is standard. Neither is waterproof. Cement backer board is grey, heavy and gritty to the touch.
- Rule out standard plasterboard immediately.In a shower it will get damp through the grout, the gypsum core softens, and the fixing of the tile adhesive to the paper face fails. It is the single most common cause of a failed shower wall.
- Treat moisture-resistant board as a starting point, not a solution.MR board resists occasional dampness. It is not designed to sit permanently wet, and every manufacturer specifies a waterproof membrane over it in a shower enclosure.
- Prefer a backer board in a new installation.Cement or XPS foam backer boards are unaffected by water, are designed for tiling, and take heavier tiles. In a shower they are the right answer and are not expensive.
- Check the weight limit before choosing tiles.Plasterboard on studs is typically limited to around 32kg per square metre including adhesive; cement backer board to considerably more. Large-format porcelain gets heavy quickly.
- Check the stud spacing.Boards intended for tiling usually want studs at 400mm centres rather than 600mm. A springy wall cracks grout however good the board is.
- Tank whatever board you use in the wet area.Primer, membrane, and reinforcing tape at every corner and penetration. This is what actually keeps water out of the wall.
- Prime before tiling if the board requires it.Paper-faced boards absorb water from the adhesive, which weakens the bond. Follow the adhesive manufacturer's priming instruction.
- Use the right adhesive.A cement-based flexible adhesive, not a ready-mixed tub adhesive. Ready-mixed dispersion adhesives re-emulsify when persistently wet and are not suitable for showers.
Tips
- Calculate tile weight per square metre from the manufacturer's figure and add roughly 5kg for adhesive and grout before comparing it to the board's limit.
- Ready-mixed tub adhesive is fine for a dry splashback and wrong for a shower. Check the tub for wet-area suitability.
- If you are stripping a shower wall anyway, replacing the board with backer board costs very little more than the membrane alone.
Common mistakes
- Assuming moisture-resistant board is waterproof — It resists dampness in humid rooms. It is not designed for a surface that gets water through the grout every day, and manufacturers specify tanking over it in showers.
- Using ready-mixed adhesive in a shower — Dispersion adhesives soften when kept wet. In a shower area they gradually lose grip and tiles come away, usually years later and all at once.
If it doesn't work
Tiles sounding hollow in a shower
Cause: Adhesive bond failing on a damp board — Fix: Strip that area back to the board, replace it and tank before retiling.
Board feels soft when pressed
Cause: Saturated gypsum core — Fix: It has to be cut out and replaced. It does not recover on drying.
Grout cracking in straight vertical lines
Cause: Board joints moving, or studs too far apart — Fix: Cracks over board joints mean the substrate is flexing; the wall needs stiffening, not regrouting.
Tiles sliding down the wall while fitting
Cause: Too heavy for the adhesive or the board — Fix: Check the weight per square metre against the board's limit and use tile supports while it sets.
Questions people ask
What is the maximum tile weight on plasterboard?
Commonly quoted as around 32kg per square metre for plasterboard on studs, including adhesive and grout, but always check the board manufacturer's figure. Cement backer board carries considerably more.
Can I put backer board over existing plasterboard?
Yes, and it is a common approach — the backer board is screwed through into the studs, so locate them first. It builds the wall out, which affects the tray, the door and the window reveals.