damp proofing a room

RonTT wrote on Thu Aug 20, 2026 8:36pm:

Airflow/ventilation while the house is empty is a must. As flyingduck says move furniture away from walls it does help

Badger1234 wrote on Thu Aug 20, 2026 6:27pm:

It's not that straightforward, imo.

We left our place in late March and came back a few weeks later to find it looking like we'd had a flood. We had 3 door frames swollen so much the doors wouldn't shut and one room plastered in mould.

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Not much we can do about the door frames and I think they need replacing, but with the mouldy room, we painted over with anti damp paint and then normal paint.

We'll see if that's any good when we go back over in a couple of months.

That time, we'd made sure that all windows and doors were closed and I think that was our particular mistake.

When we left last time, we left all the shutters fractionally open, along with the windows and made sure all the doors were open.

I don't envisage a problem on our next visit, because it's been constantly warm, but who knows?

Anyway, If the place still goes damp in the upcoming winter, I'll be at a loss in knowing what to do.

Hence me being interested in any replies.

aitchc1401 wrote on Fri Aug 21, 2026 12:59pm:

We were advised when we first bought in Spain to get air vents in all rooms and leave them open when we leave, plus leave all doors open between rooms. Leave wardrobe doors open as well. Never had a problem since we did this.

At the time it cost 50 euros per vent, covered the cost of the round hole cutting and vents fitted either side of the opening. That was 2018 so I am sure it will be more now....

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...

  Afterwards I fitted closable vents on the inside of the vents we had fitted, so that we can close them whilst we are there in the winter, otherwise it gets very draughty.

After we use the shower or bath in winter we always leave the bathroon window open until any steam and cleared, with the b/room door closed to stop condensation circulating around the house.

Rgds,

Aitch.

Badger1234 wrote on Fri Aug 21, 2026 1:44pm:

We do have vents inside on the roller shutter boxes, but they're only small. I think they're pretty ineffectual and need fans.

Thinking about it, I'm going to look into that when we next go over. 4" fans powered by solar panels sounds the way to go, I think.

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I do like a not too difficult project to potter about with when I'm over there.

Deancaro wrote on Wed Aug 26, 2026 11:37am:

Hi Steve,

We had exactly the same problem in our underbuild. Because you have done the waterproofing on the outside you just need to get rid of the excessive moisture inside. As others have already said, ventilation is key (we installed two separate powered air vents) but to also help we put a dehumidifier...

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... in the underbuild 24/7 whilst we were there on holiday. You have to manually empty the water out each time it is full but over time it eventually got rid of the excessive moisture content meaning the mould and damp smell disappeared. It was only then (approx 6-9 months later) that I redecorated and everything has been fine since, but I still run the dehumidifier from time to time just because I do not have any outside windows down there and would hate to see the mould come back. It also shows a humidity reading of the room in a percentage. The ideal humidity should be between 45-50% for comfort and mould prevention.

Hope this helps.