Condensation and mould myths
There's a lot of folk wisdom about condensation. Some of it is harmless; some wastes money or makes things worse. Here are the most common myths and what to do instead.
1. "A bowl of salt (or rice) will soak it up"
Salt and rice absorb a tiny amount of moisture from the air. Compared with the half a litre or more two sleepers breathe out overnight, it's negligible. Save your salt.
2. "Moisture-absorbing crystal tubs fix condensation"
Calcium chloride tubs do collect visible water, which looks convincing. But a typical tub gathers a few hundred millilitres over weeks — less than a single night's moisture in a bedroom. They're useful in small, closed spaces such as a wardrobe or caravan, not for a room.
3. "Close the vents to keep the heat in"
Closing trickle vents and blocking air bricks traps moisture indoors. Background ventilation costs little heat and is often the difference between dry walls and mould. See ventilation explained.
4. "Turning the heating up gets rid of the moisture"
Warmer air holds more water, so the humidity reading drops — but the water is still there. Heating does help by warming surfaces above the dew point, but on its own it's an expensive way to manage a moisture problem. Removing moisture and ventilating usually does more per pound.
5. "Bleach kills mould for good"
Bleach can lighten the stain on hard, non-porous surfaces, but on plaster, wood and silicone it doesn't reach growth below the surface, and it won't stop mould coming back if the conditions stay the same. Follow safe cleaning guidance (see black mould) and fix the cause.
6. "Anti-mould paint solves the problem"
Anti-mould paint can delay regrowth on a clean surface, which is useful. But if the wall still sits at high humidity for long periods, mould returns — usually around the edges first. Treat it as a finish, not a fix.
7. "Double glazing causes condensation"
Double glazing makes the glass warmer, which reduces condensation on windows. What can change is airtightness: new windows remove draughts that were ventilating the room, so moisture builds up and appears on walls instead. The fix is ventilation (trickle vents open), not single glazing.
8. "Condensation on the outside of my windows means they're faulty"
The opposite. External condensation on cold, clear mornings happens because efficient glazing keeps heat in, so the outer pane gets cold. See window condensation.
9. "A damp-meter reading proves rising damp"
Most handheld damp meters are calibrated for timber. On masonry, salts and some materials they give high readings that don't prove rising damp. Low-level damp has several possible causes, and an injected damp-proof course won't fix most of them. Read damp or condensation? before agreeing to treatment.
10. "Condensation is caused by the way you live"
Everyone breathes, cooks, washes and dries clothes. UK health guidance is clear that damp and mould shouldn't be treated as a lifestyle problem: homes need adequate ventilation, heating and insulation for normal use. Habits can help, but if a home can't cope with ordinary living, that's a building issue — and for renters, often a landlord's responsibility (see renters' rights).
What actually works
- Measure humidity for a week or two so you know what you're dealing with.
- Reduce moisture at source — especially drying clothes indoors.
- Make extraction and background ventilation work properly.
- Keep cold surfaces warmer: furniture off walls, steady heating, insulation done well.
- Rule out leaks and rain penetration before any condensation treatment.