The paint is coming off the bathroom wall in sheets: why, and the sequence that lasts

Peeling paint is almost never a paint problem; it is a moisture or surface problem wearing paint's clothes. The bathroom is the house's champion at both, which is why the same wall re-peels through three expensive repaints until the sequence below is done in the right order, with the right patience for the drying step that everyone shortens.

Diagnose in three minutes

• Where it peels tells you the cause. Peel at the bottom third, near the floor or outside-wall base: rising damp or a shower leak finding the low path. Peel behind the shower wall on the other side: water is crossing the wall and the paint is the membrane it escapes through - check the grout and the silicone bead around the tray first (the ripple article's logic, one wall away). Peel everywhere at once after a holiday with the windows shut: the room lived on its own steam - the condensation article's territory - and the paint just kept the score.
• The foil test, overnight: tape a square of kitchen foil to the wall, tape all edges, check in the morning - water on the room side, condensation; water behind the foil, the wall is carrying it from outside or within. The two answers need different fixes and no amount of paint distinguishes them.
• White crust with the peel (efflorescence): that is cement's salts arriving with the water and staying when it dries. It is the one that specifically punishes painting through: paint over salt and the new coat inherits the eviction.

The redo sequence, no shortcuts

One: fix the water - the leak, the grout, the ventilation - or delete this list from your plans because you are repainting a clock. Two: scrape every loose edge to firm paint, sand the feather, and - this is the step everyone skips - wash the whole panel with detergent, rinse, and let the wall dry on its own for at least several days with the windows open; a wall that is dry to the paint tester's cheap meter can still be wet behind the render and the meter's numbers are what to watch, not the calendar. Three: prime - and the primer here has a name to ask for: an alkali-resistant or stain-blocking primer on cement render (ordinary emulsion on fresh render is eaten by the same salts above, and "it drank the paint" is that conversation), and a proper anti-mould primer where the bathroom black has lived. Four: two thin coats of bathroom-rated emulsion, not one heroic one, and the fan or window running for the week after - the coat cures against moisture, and a shower in a freshly painted box on day two is a shortcut that re-opens the cycle.

What this desk won't pretend about ventilation

A bathroom with no window and no extractor is a condensation machine no product fixes; an extractor door to the outside beats one dumped into the roof space, and a trickle vent kept open costs nothing and outperforms every "anti-mould paint" claim, which are sold as a coat and delivered as an excuse. If the peel keeps winning after a correct sequence done honestly, the wall is getting water you cannot see from a leak you have not found - that is the investigation this page sends you off to make, and the leak-detection people with their cameras are the last, right answer.