Mould and damp in your holiday home: a humidity problem, not a dirt problem
The first thing many people think when they see dark patches in the holiday home is that the place is dirty. But mould on the North Sea coast is nearly always a damp problem, not a dirt problem. A closed house, damp coastal air and wide temperature swings produce condensation, especially in the low and shoulder seasons. It is about the moisture in the air, not about dirty surfaces.
Why it happens here in particular
When the house stands empty the temperature drops, and the damp air meets cold surfaces. The water condenses on walls, in corners and behind furniture. That is why mould often appears in a house that looks perfectly clean.
The coastal climate makes it worse in two ways. The air is damper than inland all year round, and the temperature swings more, because these houses are light and often poorly insulated compared with a year-round home. A holiday home is built to be warm and aired in summer, not to stand cold and shut for five months.
So it is not a sign of bad cleaning either. We see mould in houses that were thoroughly cleaned in October, precisely because cleaning has nothing to do with it.
Bleach is the trap
A classic mistake is chlorine bleach. It removes the dark patch but does not kill the spores deep inside porous materials such as wood, plasterboard and grout. If you do not keep the damp down the mould returns, and then people think it has got worse when in truth it never left.
Treating the patch alone is a waste of time. It is like mopping up under a leaking tap without turning the tap off. Find the moisture source first and treat afterwards.
And never mix bleach with acid, whether vinegar, citric acid or descaler. It releases toxic chlorine gas.
The hidden places nobody airs
The worst place is closed cupboards and wardrobes against a cold external wall. The air stands still and condensation forms where you cannot see it, until the clothes smell.
- Leave cupboard doors, wardrobe doors and internal doors open when the house stands empty, so air can circulate.
- Pull furniture a couple of centimetres off external walls so air can move behind. The sofa against the north wall is the classic.
- Buy a cheap hygrometer and keep relative humidity below about 60 percent. Almost nobody has one, but it is the best early warning you can buy for the price.
- Leave a vent or a window ajar in the low season. A completely sealed house in winter gets mould.
- Wipe the rubber seals in the washing machine and dishwasher and leave the doors ajar between visits.
- Stand mattresses and cushions on edge or lift them off cold surfaces so they do not lie flat and collect condensation.
How to work out where the damp comes from
There are three sources, and each needs a different answer. Condensation comes from inside and is solved with air change and a little heat. Leaks come from outside, through the roof, windows or the base of the wall, and must be repaired. Rising damp comes from below and is a building problem.
You can usually tell them apart like this: condensation mould sits in corners, behind furniture and on cold surfaces, and is worst in winter. A leak gives a defined patch, often on a ceiling or under a window, and gets worse right after rain. Rising damp starts at floor level and moves up in an even line.
What works, and what does not
There are three answers that genuinely change something, and they are all about air rather than about products.
Air change is the cheapest. A vent left open, or a window ajar in one room, does more than any spray. The point is not to let cold in but to let the damp air out, and that needs only a small opening if it stays open all the time.
A little heat is the next best. Warm air holds more moisture than cold, so a few degrees of background heat means the damp stays in the air instead of settling on the wall. It is not free, but it is cheaper than mould remediation.
A dehumidifier is the surest if the house is hard to air or sits very exposed. It needs a drain or emptying, otherwise it stops when the tank is full and simply stands there using power.
What this means for a house that is let
A let house has one advantage and one disadvantage. The advantage is that people come regularly, and every guest airs the place, turns the heat on and uses the house. The disadvantage is that guests also produce moisture: showers, cooking and wet towels, and they typically leave without airing behind them.
So the changeover is the right moment to look. It takes two minutes to check the cupboards against the north wall, behind the sofa and under the windows, and that is exactly where a starting patch shows first. Caught there, it is a cloth. Caught in spring, it is a tradesman.
If you do have to treat real mould
Wear a mask, and do not brush dry patches, because that throws spores into the air. Wash gently and air the room thoroughly afterwards. Take textiles out of the room first so they do not collect what you loosen.
If the growth is large, sits deep in the material, or returns in the same place after treatment, have a professional look at it. It is no longer a cleaning question.
The safest answer is catching it early
Our holiday home cleaning keeps an eye on the vulnerable places, and a house check in the low season finds damp before it spreads. We are a local cleaning company based in Bork, covering Hvide Sande, Søndervig, Henne Strand, Nymindegab, Blåvand, Bork Havn, Hemmet, Skjern, Tarm and Ringkøbing. Get in touch to hear about an out-of-season check.