To stop condensation on walls, you need to do three things: reduce the moisture in the air, improve ventilation, and keep wall surfaces warmer so warm air stops turning to water when it touches them. Condensation on walls forms when humid indoor air meets a cold surface — and if it's left alone, it becomes the leading cause of wall mould. This guide covers what causes it, how to stop it room by room, and how to repair walls it has already damaged.
Key Insights:
- The cause is simple physics: Condensation forms when warm, moist indoor air hits a cold wall — most common in winter, and in bathrooms and bedrooms.
- The fix is airflow, warmth and less moisture: Ventilate the room, keep it evenly heated, and cut the humidity at its source.
- It's the number one cause of wall mould: Left unchecked, condensation feeds mould within days, so stopping the damp is what stops the mould.
- Paint alone won't fix it: Repainting a damp wall fails quickly — fix the condensation first, then protect the surface with a mould-resistant paint.
What causes condensation on walls?
Condensation happens when warm, moisture-filled air touches a surface that's colder than it is. Warm air holds a lot of water vapour; when it cools against a cold wall, it can't hold that moisture any more, so the water is released onto the surface. It's the same reason a cold glass sweats on a warm day.
Cold external walls, single-glazed windows, poorly insulated corners and the wall behind furniture are the usual hot spots, because those surfaces stay coldest. Everyday activities pour moisture into the air too — showering, cooking, drying clothes indoors and even breathing overnight. In cooler, damper areas like the Blue Mountains, the gap between warm indoor air and cold winter walls is wide, which is why condensation peaks in the colder months.
How do you stop condensation on walls?
Stopping condensation comes down to attacking it from three directions at once — more airflow, warmer surfaces, and less moisture in the air:
- Ventilate every day. Open windows for 10–15 minutes morning and night to let humid air escape, and run exhaust fans in the bathroom and kitchen.
- Keep rooms evenly heated. A little consistent background warmth keeps walls above the temperature where condensation forms — far better than letting a room go cold then heating it fast.
- Reduce moisture at the source. Cover pots while cooking, dry washing outside rather than indoors, vent the clothes dryer outdoors, and keep shower times short.
- Move furniture off cold walls. Leaving a few centimetres behind wardrobes and beds on external walls lets air circulate and stops damp pockets forming.
- Use a dehumidifier in rooms where condensation is persistent.
Do these together and most household condensation clears up. The signs of mould behind paint are worth watching for while you sort it out, because condensation and early mould often appear in the same spots.
How do you reduce humidity in the house?
Lowering the overall humidity in your home is the most effective long-term way to prevent condensation. Aim to keep indoor humidity somewhere between 40% and 60% — high enough to be comfortable, low enough that walls stay dry.
The practical steps are the same moisture-cutting habits applied across the whole house: ventilate wet rooms, dry clothes outdoors, use extractor fans, and run a dehumidifier in problem areas through winter. Good airflow between rooms helps too — leaving internal doors open lets moisture-heavy air disperse rather than settling on one cold wall.
How do you stop condensation on bedroom walls?
Bedrooms are a common condensation trouble spot because they're often kept cooler and closed up overnight, while sleeping adds a surprising amount of moisture to the air. It typically shows up on external walls and in corners behind wardrobes.
Crack a window overnight or in the morning to let the moist air out, pull large furniture a few centimetres off external walls, and add a little gentle heating to keep the walls from getting cold enough to sweat. These small changes make a big difference in Blue Mountains and Hills District bedrooms through winter.
Does condensation cause mould on walls?
Yes — condensation is the single most common cause of mould on interior walls. Once a wall stays damp from condensation, mould spores have the moisture they need and can take hold within a couple of days, usually appearing first as black or grey speckling in cold corners and behind furniture.
This is why treating the mould without stopping the condensation never lasts: the damp keeps coming back, and so does the mould. Fixing the airflow, warmth and humidity is what actually breaks the cycle.
How do you fix walls already damaged by condensation?
Once condensation has left damp patches or mould, the repair follows a clear order: stop the condensation, let the wall dry completely, treat any mould, then repaint. Skipping straight to paint over a wall that's still damp only traps the moisture and the fresh coat fails within weeks.
When you do repaint, a mould-resistant paint made for high-humidity walls adds a protective barrier that standard interior paint can't match. This is also where a professional interior painting job earns its keep — proper preparation deals with the damp and the mould first, so the finish actually lasts.
When should you call a professional?
Bring in a professional if condensation is severe or constant, if walls stay wet no matter what you try, or if mould keeps returning after treatment. Persistent condensation can point to deeper issues — poor insulation, a cold-bridging wall, or a building that simply doesn't breathe well — that need more than everyday ventilation to solve.
A professional can also prepare and repaint the affected walls correctly with the right moisture-resistant system, so you're not repainting the same patch every winter.
Frequently asked questions
What causes condensation on walls? Condensation forms when warm, humid indoor air touches a colder wall surface and releases its moisture as water. Cold external walls, single-glazed windows and poorly insulated corners are the usual spots. Everyday activities like showering, cooking and drying clothes indoors add the moisture that feeds it.
How do I stop condensation on my walls permanently? Permanently stopping condensation means keeping humidity down, walls warmer and air moving. Ventilate daily, heat rooms evenly, dry washing outdoors, use exhaust fans, and keep furniture off cold external walls. Where it's persistent, a dehumidifier or better insulation raises the wall temperature so moisture stops settling.
Does condensation always lead to mould? Not always, but it's the most common cause. A wall that stays damp from condensation gives mould the moisture it needs to grow, often within a couple of days. Keeping walls dry through ventilation and warmth is the best way to stop mould before it starts.
Why do I get condensation on my bedroom walls? Bedrooms are usually cooler and closed up overnight, and sleeping adds moisture to the air, so it condenses on cold external walls and in corners. Cracking a window, adding gentle heating and moving furniture off external walls usually fixes it.
Can I just paint over condensation damage? No. Painting over a damp or mouldy wall traps the moisture and the paint fails quickly. Stop the condensation first, let the wall dry fully, treat any mould, then repaint with a mould-resistant paint for lasting protection.
Stopping condensation on walls comes down to three things done together: cut the moisture in the air, keep the room ventilated, and keep the walls warm enough that moisture stops settling. Deal with the damp and you deal with the mould at the same time. If condensation keeps returning in your home, or you'd like the affected walls repaired and repainted properly, Decor8 offers free onsite quotes across the Blue Mountains, Western Sydney and the Hills District — you can request a quote or call John on 0404 842 708.
Decor8 Painting & Decorating — servicing the Blue Mountains, Western Sydney & the Hills District.