Damp, Mould and Cracks: How to Prep Bangkok Condo Walls Before Painting

Bangkok is hard on walls. High humidity, aggressive air-conditioning that pulls moisture through plaster, towers that flex a little every day in the heat, and bathrooms on the other side of most bedroom walls. When a repaint fails here — bubbling, flaking, a stain coming back, black spots at the ceiling — it is almost never the paint. It is what was under it.

This is what a crew should do to a Bangkok condo wall before the first coat goes on.

Step one: find the water

Every brown, yellow or grey stain gets a moisture meter on it before anything else. A reading above roughly 16% on plaster means the wall is still wet, and paint will not stick to a wet wall no matter what the tin says.

The usual sources in a condo:

• The bathroom next door — yours or the neighbour's. Failed grout or silicone lets shower water into the wall. This is the number-one cause of bedroom stains in Bangkok towers, and regrouting the bathroom is the fix, not painting the bedroom.
• Balcony and window joints — sealant that has dried out lets rain in during the wet season.
• AC condensate — a blocked drain line drips inside the wall behind the unit.
• Rising damp on ground floors — townhouses and older low-rises in Ari, Phaya Thai and Thonglor.

If the source is on your side, it gets fixed first. If it is the neighbour's, you need the reading and photos to take to the juristic office — which is why a good crew records them in the report.

Step two: kill the mould, don't cover it

Black or green spotting near ceilings, behind wardrobes and around window frames is mould living on the paint film. Painting over it is pointless: spores come through the new coat in weeks, and "anti-mould" paint only slows regrowth on a wall that is already clean.

The wall has to be washed with a fungicidal solution, scrubbed, rinsed and left to dry — usually overnight with the room ventilated. Only then does primer go on. Anti-mould additives in the top coat are worth having in bathrooms and north-facing rooms, but they are the last step, not the first.

Step three: cracks that move need to be treated like cracks that move

There are two kinds of crack in a Bangkok condo. Static ones — a chip from a picture hook, a dent from a sofa — fill with ordinary filler and stay filled. Moving ones — the hairline along the ceiling, the diagonal off a door frame, the line where two walls meet — open and close a fraction with temperature every day. Rigid filler in a moving crack snaps within a season.

Moving cracks are raked out to a V, filled with a flexible acrylic filler or bridged with mesh tape and a thin skim, then primed. It takes longer and it is the difference between a crack you see again in six months and one you do not.

Step four: chalky, glossy or patchy plaster

Old paint that comes off as powder on your hand is chalking; new paint will not bond to it. It needs washing down and a bonding primer. Old gloss or semi-gloss needs sanding so the new coat has something to grip. Walls patched by previous tenants with a different sheen show through every repaint until they are skimmed level.

On older stock a thin skim coat over the whole wall — a few millimetres of plaster or filler sanded flat — is what produces the glass-smooth surface people mean when they say a wall looks new. It is not always needed on a five-year-old condo. It almost always is on a twenty-year-old one.

Step five: prime what needs priming

Filler, skim, bare plaster and any treated stain get a sealing primer. Without it, the top coats soak in unevenly and dry patchy, and old stains bleed back through. This is the single most skipped step in cheap paint jobs because it adds a drying cycle to the day.

How to tell if your painter is doing this

Ask to see the moisture meter. Ask what they do with cracks along the ceiling line. Ask whether primer is in the quote. A crew that prepares walls properly will talk about it happily, because it is where the work is. A crew that does not will talk about how fast they are.

RenoRova's wall repair is quoted per wall after a look at the cause, with the readings and before/after photos in your report, and the 2-year guarantee covers the paint on top. If you are not sure whether your walls need repair or just paint, send photos on LINE — a crew lead will tell you which before you book.