I asked about this on here a couple of years ago. Thread here.

We continue to have problems with condensation and mildew in our apartment in northern Spain. We've tried getting the tenants to ventilate and use a dehumidifier, but they are still getting mildew on some of the exterior walls in the winter.

We are now thinking about trying the solution from the company Hogar Seco. Has anyone had any experience with them? Or can recommend any other companies that could provide a solution?

Thanks.
- Eric S.

We had the same issue. There were no (obvious) problems on the outside of those walls.

In the end we built a 'camra' or false wall on the inside with a gap between the two. This completely solved the problem (or at least hid the problem).

Or perhaps for a quick and simple sort of solution line the walls with a 2 or 3mm thick polystyrene roll, similar to wall paper but thicker and of course more insulating.
It is easy to hang and quickly painted with an emulsion paint. Stops the condensation and can be renewed as needed.
It has helped me on outside walls of tenanted properties where condensation was a problem before.

Worth a try if not already in place and a fraction of the cost and fuss of some other supposed remedies.

Are you certain that it is condensation? We had a bedroom outer wall with a bad mould problem. I tracked it down to a hidden concrete gutter channel running along the front of the house. Lifting the tiled cover we found that the gutter was not sealed at the bedroom wall end. To make matters worse there was no fall to the channel. When it rained a proportion of the roof water was running back into the bricks and seeping along the wall causing the dampness. My builder chap built the channel up slightly to give a fall and sealed the end at the same time. No problems since. Even if you don't have such a rain channel it might be worth inspecting the outside wall and see how rainwater gets away.

Yes, we're sure it's condensation. The tenants say the walls look like a bathroom mirror after taking a shower.

- Eric S.

Eric,what is the tenants problem with using a dehumidifier.? Noise perhaps? We have a similar problem with an elderly relative staying. We areconsidering getting a dehumidifier as opening windows is a problem (lets in the cold). We do have an extractor on the bathroom.

Can you identify the source of the moisture? Are they using butane gas heaters?

It could simply be their breath if they don't have adequate ventilation.

That's a lot of heavy breathing!

We've provided them with a dehumidifier and asked them to ventilate. But we can't depend on them to do it. Or, they are doing it and it's not enough to solve the problem. So that's why we are looking into other solutions.

Thanks
- Eric S.

Dehumidifiers dont work, end of, you have to reduce the situation that allowscondensation to occur, the cold surface that the moisture condenses upon.

Here we have incredibly high moisture in the air, evening drops in temperature inevitably causes condensing onto any cool surface. The solutions are building like a boat, using teak and stainless steel a lot, utilising breezes and ensuring they are maximised, surfaces that keep warm in the evenings and to an extent dont care like thick concrete walls, never using traditional plaster over anything or absorbant paints like whitewash, and avoiding quick fixes like polystyrene - unless its structural grade a few inches thivk and aluminium surfaced, even then concretes better.

Oh, if you do use concrete, dont paint it, unless you know its breathable but cant absorb water, concrete can be many colours determined by the sand its made with, and pigments in the mix, but avoud painting it if possible where condensations an issue. Tiling it can work but treat it like a pool, epoxy or cement base grouts.

If the issue is like the uk - bathrooms - ventilation from the warmer inside to outsides the cure - good extractor fan, and double glazing - minimising cold surfaces for condensation to form - thick polystyrene insulated but impervious walls - again - concrete beats plaster any day - you can get impervious concrete based board instead of plasterboard then skim it with mortar.

Thanks for the input. However, this is an existing apartment, not a new build. So we don't have a choice of the building material.

We're looking at what we can do now, given what we have. We want to make sure that what we do will be no maintenance, because we can't depend on our tenants to do anything.

It seems like we have two options:

1. Add some kind of insulation to the walls so that the surface will not be so cold in winter and therefore reduce or eliminate the condensation.

2. Use some kind of ventilation and/or de-humidification system to reduce the humidity inside the apartment.

We'd want to whichever was more cost effective. Number 1 would probably be a lot more involved. But number 2 would mean increased electricity costs.

I was asking here about Hogar Seco, because they have a system for solution #2. But I guess no one here has any experience with them.

Thanks.
- Eric S.

I simply don't agree - dehumidifiers work just fine - when used properly!

I used one to dry out an apartment after the previous tenant left all the taps on, windows closed etc. It took a week but it worked. We were then able to repaint.