Condensation / mould issues in older house

[peachgreen]

Our house is 1950s poured no fines concrete. When we moved in we knew there were damp issues. Pulled up the lounge floor (at the front of the house, north facing) and found a big cavity underneath with loads of rotten woodwork. Someone had half-heartedly fitted a damp membrane but hadn't cleared the air bricks or dried it out properly in the first place so it hadn't helped much. We dried it out, had a damp treatment and membrane put in, cleared the air bricks, had the floor redone (including joists etc), took all the exterior walls right back to bare concrete, applied damp treatment and had them replastered (all by professionals).

This is our first winter since it was done and we're getting issues with condensation and mould at the bottom of the exterior walls. Is this to be expected given we've had the whole thing redone? Is there anything we can do besides wiping it down regularly and treating with mould and mildew? We keep the house well-heated but rarely have the windows open at the front as we live on a busy road.

Hi peachgreen. I've just been reading a bit about no fines concrete homes, and it says on the link that the quality of thermal performance tends to be poor so a lot of concrete houses have been found to suffer from excessive heat loss and surface condensation leading to mould growth. I'm no expert by any means whatsoever(!) and I don't know if this is definitely what's been happening in your home, but we had an identical problem when we first moved in to our Victorian semi which has solid brick walls. The condensation/mould actually got worse after we'd installed double glazing and central heating (we'd effectively sealed all the draughts out and the moisture in; and it didn't help that the house was now kept at a constant temperature because the heat was still flying straight out through the outside walls). In the end, we decided to try a dehumidifier which we kept running 24hrs for the next couple of weeks, and the condensation vanished. This was 30-odd years ago, and we've managed to keep it at bay ever since just by using the dehumidier from autumn through to when the weather warms up in spring.

I don't know if this might help you as a temporary solution until somebody more knowledgeable than me comes along with a better answer? Good luck in any case, I hope you can get it sorted.

If you've got damp under the ground floor after you've cleared the airbricks, it's probably a water leak.

Have you got a water meter?

If it changes with the weather, rainwater may be running in, e.g. from badly designed drive or paving or drain.

Thanks @mushrumpmania - a dehumidifier has helped in the conservatory so we might have to bring one inside and see if it clears the issue. It definitely feels like condensation and there's no paint bubbling etc so it seems like it's surface water so that makes sense.

@PigletJohn No water meter but we did get a plumber in who said he didn't think we had a leak anywhere, and the water board agreed. Our drive (gravel) does tend to flood when it rains so that could be part of the problem - it doesn't come up to the house but is definitely pretty saturated at times. Hmm. Something to think about!

It's so frustrating as we spent so much money getting the problem sorted (the floor had literally rotted away and the plaster was crumbling at the touch) and I'm just afraid it'll get that bad again!

Does your boiler have a pressure gauge? Have you got loft tanks?

Have another look under the floor. Add a handy access hatch this time.

@PigletJohn Boiler pressure is fine - we did have issues but bled all the radiators and it's been stable ever since. No loft tanks (well there's an old one but it's empty).

Yuck, the thought of taking up the carpet and floor again is a bit depressing but if we must we must! Thank you!

Have you had a word with neighbours to see if anyone else is having similar problems to your own? I found a lot of links to specialist building firms when I googled, many of them gave details of remedial work that could be done to help with no fines problems and one of these was the addition of exterior cladding, which gives some insulation as well as protects against rain penetration. Again, I'm not qualified to give actual advice, but it does sound to me like you've ruled out the possibility of underground seepage now so could it be that the humidity in your home is that much higher because some rain is getting through somewhere?

That said, all of our own walls were sound when the condensation problem was at its worst here, ditto the guttering and the roof, so it was just down to everyday living - cooking, showers/baths, drying washing indoors in the winter, even breathing. The previous owners had taken to using polystyrene ceiling tiles to line the walls of the bathroom in order to provide some insulation, and they'd used wooden cladding everywhere in the kitchen for the same reason. All of the plaster on the exterior walls in our lounge and dining room was completely blown when we stripped off the existing wallpaper there and we had to do the same as you, take the walls right back to bare brick then replaster. I would never have believed that condensation could do so much damage to a place, but I guess it's one of the perils of living in certain types of properties.

Our dehumidifier is powerful enough to use in a 4-bed house (ours has just 2!) and we leave all internal doors ajar during the day so that it can deal with the air in the bedrooms as well. It's been the cheaper option from our point of view, adding any kind of interior/exterior insulation to our place would not only be costly, but it would start to reduce the space as well and we're quite short on that as it is.

Ah thanks so much @mushrumpmania, really kind of you. It's already clad and as far as we / the surveyor can tell the cladding is sound - besides, we have issues in too many places for it to be the cladding I think (bathroom also has terrible condensation issues, paint peeling away etc but that's partly because they've used awful quality paint). I actually think a dehumidifier might be our best bet for now - I might look into a bigger one and see if we can leave it running somewhere. It's definitely got worse as it's got colder outside / warmer inside and besides yesterday we haven't had a huge amount of rain.

Funnily enough the previous owners here had also covered several of the more problematic walls with polystyrene - total nightmare to get off and of course the plaster behind was completely blown, just crumbled away as you touched it. We needed so much of it replastered, it was a nightmare.

peachgreen I feel your pain! Polystyrene tiles are horrible and a H&S nightmare, the fact your house had them too does seem to point towards an ongoing condensation issue though rather than other kinds of damp doesn't it? Good luck with the dehumidifier, I hope it works out as well for you as it has for us xxx