I have an old house in the countryside and the walls are always damp, especially in winter. The paint starts to peel and I smell mold. I've already tried opening the windows but the problem persists. What can I do to solve this effectively?
The problem goes deeper than it looks. Opening windows helps, but if the humidity persists it's because there's serious infiltration or condensation happening. First, check whether the water's coming from outside (infiltration in the foundations, broken tile, clogged gutter) or if it's interior condensation (poor ventilation, weak insulation). Old houses usually have problems at the base - water rises up the walls through capillarity. If the walls get damp near the ground and the humidity rises to a certain height, that's it. Scrape off the peeling paint with a scraper, let the walls dry properly (it can take weeks) and then paint with anti-mold paint or silicate paint that lets the wall breathe.
If it's condensation (bathroom mirrors fogging up, mold in the corners), you need better air circulation - extractor in the kitchen, ventilation in the bedroom. Dehumidifiers help temporarily but don't solve it. The ideal thing is to create airflow, open windows on opposite sides and avoid drying clothes inside the house. If the house is too shut up in winter, you've got to take the risk - it's worse to leave it unventilated in the cold than to have permanent mold.
As for a serious solution, it's worth investigating the foundations and exterior coverings. If the leaks are actually coming from outside, no paint will fix it - you need to fix the source. Sometimes it's as simple as cleaning the gutter or fixing a tile. After that, if you decide to do a more robust treatment, there are resin injections in the walls to stop rising damp, but it's more expensive. Start with the basics: check for infiltrations, improve ventilation, let it dry and repaint with proper materials.
The problem is almost always condensation building up combined with poor air circulation, and in old houses it gets worse because the walls absorb a lot of moisture from the ground.
Before spending money on expensive solutions, try improving ventilation - it's not just about opening the windows once in a while, it's about keeping them open more regularly, even if you lose a bit of heat, and put dehumidifiers in the worst spots (the cheap ones with gel work pretty well).
If mold is already there, clean it with an antifungal product and then only anti-humidity paint will fix it, but without sorting out the ventilation properly the paint will peel off again.
If the humidity is really coming from below (from the ground), then you need serious waterproofing - it could be a resin injection into the walls - but that's more for when other things don't work.
Have you checked whether the house foundations have drainage or if the ground around it is holding water? Because even if you open windows, if the wall is pulling moisture from the soil (which is common in old houses without waterproofing), no amount of ventilation will fix that on its own. It might seem expensive, but sometimes the solution is to waterproof the baseboard from the outside or dig a drainage trench around the perimeter - depending on how much money you're willing to spend. If it's just condensation, an electronic dehumidifier helps in the short term, but the root cause is always to eliminate the source of the moisture.
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