Where does the damp patch come from!?

[dampannoyed]

We have a damp patch in our kitchen that we’re desperate to fix – any ideas as to what it could be would be most welcome… feels like we’ve (and various companies!) have checked everything and they’re about to give up but we can’t :-(

There’s been a small but growing damp patch on the kitchen wall for a few years. Just over the skirting boards, where there used to be a hearth (long time ago, before our time). The chimney’s long removed too.

Last year the mains pipe going into the house leaked under the floor. It was easy to fix but the floor was ruined. One of the companies inspecting the damage thought the damp patch (which grew much more over this time– it took a while to fix because of covid) was related to the new(ish) leak. A big area of plaster was removed (maybe an inch thick?) and we got fans to dry the area out, which fixed most of it but there is this one remaining patch that just does not go away after several weeks with fans + a long time after that. It doesn’t seem to get any worse, but not any better either. So that wall hasn’t been repainted yet. The various companies that have been here to fix things are now clueless about what it might be/where it might come from. Any ideas would be so welcome…

There are two radiators nearby, but they do not leak, have been changed recently. There are no pipes in the wall or under the floorboards (although the floor just by this area is concrete due to the now removed hearth). There is no chimney anymore. The moisture has been checked to see if it’s ’drinking water’ or ’rain water’ but that was not conclusive, not enough moisture or something… There is no water/moisture under the floorboards (’under the concrete’ has not been checked, impossible?). The neighbours (terraced house) had a new heating system put in 5-6 years ago, and there’s a chimney on their side, but their wall’s been checked, and there’s no moisture on that side.

The kitchen itself does not feel damp, and all the other walls have been checked for moisture and there's none. The moisture can’t come out of thin air, but nobody seems to be able to figure out where it comes from… Any ideas on what to look into further from any knowledgeable people? We’re getting desperate :-(

Do you have a vent in the boarded up fireplace? If not, you could try getting one installed. If the chimney can't breathe properly, it will get damp.

I know the chimney has been removed but there is still a void there, I assume?

Photos please.

No void - the chimney must have been coming down to the floor in front of the wall (the wall is straight now), because maybe five years ago we had the ceiling painted, and they then realised that the upper part of the chimney, on the 1st floor, was 'hanging'. We were told that that was a bad way of removing chimneys, you were supposed to put some support there to stop the upper part from 'hanging' in the air if you didn't remove all of it, but that hadn't been done, so we had to put that in.

Will try to get a picture that's not too dark!

So here's hopefully a picture - thank you very much for responding, we're so grateful for any tips!

is it a wooden floor? Is the damp patch clearly associated with the position of the old hearth?

If there was formerly a fireplace or range, it is typical to have a stone or concrete slab, on a built-up section under the chimneybreast. The chimneybreast is a hollow brick rectangle, and is filled up with rubble or earth that the slab sits on. There is no DPC. So the rubble tends to draw up water from the ground below by capillary action, and it can pass into the brickwork.

If this is the case, it can be cured by removing the slab and digging out the rubble. In clean brickwork exposed to the air, damp will only rise about three courses before it evaporates as fast as it rises, so if the brick shell is exposed under the floor, and you have airbricks to ventilate the subfloor, it will usually dry out.

If you have a wooden floor and no hearth, there is no need to put a slab back, you can run joists and floorboards across the gap.

You had better verify first that there is no water leak, this might be an easier job. Was a new pipe laid under the floor? Plastic or metal? Do you know where the joints are, and if everything was replaced, or just part? Get an Engineer's Stethoscope and press it against the indoor stopcock, while someone turns the outdoor one by the road on and off. If there is a leak you will hear a faint hiss stop and start. This is best done late at night when all is quiet, using a young person with good hearing.

Bear in mind that in a semi or terrace, the leak might be in the neighbour's house.

Yes, the damp is exactly over where the concrete is, so that’s where the chimney was. The floor is cork, that’s just been laid, we had to remove the previous one and had the bare floorboards for months, they were very wet there (and whether this was only/mainly due to the leak, which was by the main pipe coming into the house, so on the other side of the kitchen, is not clear) so it took a long time for them to dry out, and some were replaced. But it was completely dry under the floorboards, though we couldn’t check under the concrete – the concrete was damp too.

I think just like you say that the chimneybreast is full of rubble – they removed the plaster outside it but didn’t open it up all the way to that. Removing the concrete slab feels like another mammoth task… is it? We’d have to remove the newly laid floor and skirting boards of course but they could hopefully be reused… :-( Odd that none of the companies that have been here have suggested this :-(

There is no more leak: since the leak was just by the mains water pipe coming into the house, that was the pipe that was changed. So nothing was laid under the floor, the issue was on the other side of the kitchen. One of the companies thought water had filled up under the floorboards and caused damage there too, but we’re not sure.

They have checked the neighbours’ side, and there was a little bit of damp there, but no obvious leak and no source of excess water. It wasn’t as bad as ours.

Thank you so much for your input PigletJohn :-)

It's quite dirty work

But not at all complicated.

Hit the slab with a big hammer and it will crack, get a pickaxe in and it will come up in man size pieces to carry away.

If the rubble is damp (likely) it will not be dusty.

It may need breaking up to loosen it, but most unlikely to be concrete, probably rubble bound together with scrap plaster, lime and sweepings.

You should not need a mechanical breaker.

It can be shovelled out into sacks and the last remains swept out. If you have a builder's vac it will suck up the sandy grit.

If you have a domestic desk fan, put it down there to speed evaporation. I expect you will notice the damp smell. you will need a cover to prevent you falling down the hole. Leave it as open as you can to speed drying, and open the windows. I hope you will start to see the dark brickwork go lighter as it dries.

I'd treat the new joists with fungicidal wood preserver as it will be damp for a while. I like to screw down the new floorboards in case you want to look down there in future. you can have a trapdoor to a wine store or floor safe if you want. If you floor it with ply you can leave it unscrewed temporarily, or hinge it.

Skirting is very cheap so no need to save the old. I would chip away any plaster behind the skirtings as it holds damp. They can be spaced off the wall on wooden battens screwed to the brickwork. Almost certain to be 18mm square.

Have a good look under the floor for any damp while it is open. Especially under the sink, and the wall next to the drain or gulley.

BTW while it is drying, you can paint the wall with Dulux Trade Supermatt. It is a porous, non-vinyl paint that allows damp plaster to dry out through it. It looks decent but is not very durable (that is not its purpose) and you can decorate over it when the wall is properly dry.

Other paint companies have similar products.

Buy that exact name, not a "similar" one.

@PigletJohn I think I love you!

Thank you so much @PigletJohn! Just the fact that someone has an idea is so uplifting, the various companies that have inspected it/tried to fix it have started washing their hands so we've just felt lost...

I found an older picture of what it looked like when it was opened to dry it out. I think this is from when it had dried a bit, but you can still see darker patches on the concrete. We had fans there for several weeks, then when they realised that didn't help we had 'heavy duty' fans and a 'tent' over the area, and that helped most of it, so to speak. We also had our own dehumidifier there for a very long time.

They did put some 'extra protection' of some kind on the wall to stop moist from coming through, and we did use Dulux Supermatt paint - not sure it was marked 'trade' though if there are different ones. But definitely Dulux matt paint.

Great idea with the fungicidal wood too. So back to removing the floor again, but having a plan makes all the difference!

Thank you so much! I'll have to second @Bonitalazenia's comment too!

I had to do exactly what @PigletJohn suggests, lots of hard graft and rubble bags but it's the only way to sort the problem

Looks strikingly similar.

Did you have plenty of airbricks to ventilate the subfloor void?

We put in an extra airbrick where the hearth was and opened up through draught areas (beneath the floorboards)to the adjoining rooms.

Thank you so much, @PigletJohn and @Somanysocks - great to hear that it worked for you. As said, just having a plan makes all the difference - we've had too many people say 'no idea'...

when the fireplace is in use, waste heat keeps it warm and dry. Even when it is not fired, the air current up the chimney sucks away a lot of damp air and encourages evaporation from the exposed brick surfaces. So it is when the firebreast is removed that there is not enough drying action, and the damp becomes noticeable. Not everybody knows this, because it is relatively uncommon, and often (unsuccessful) attempts are made to cover it up, or inject useless chemicals .

In some way , water moves by capillary action better through small pores, and is inhibited by changes in pore size as between mortar and bricks, so a clean, unplastered brick wall does not carry damp as easily as a packed mass of rubble, which is exactly what you usually find under a hearth.

The only thing that is a bit odd with that explanation is that the chimney was removed/boarded up 30+ years ago, and the issue only started very slightly maybe five years ago?

However: then remembered that our neighbours used to have an old backboiler in the chimney space (on the other side of the wall from our issue), and they removed it and put a combi boiler somewhere else. Could that have kept the problem at bay?

They don't have any issues now either but they still have the 'open chimney' there, they haven't blocked it up. Does that make sense?

might have been the backboiler keeping it warm and drawing extra ventilation up the chimney

might be that when the backboiler was removed one of the old pipes was capped off but had a slight drip.

might have been that your faulty pipe started with a small leak

Thank you very much :-) We will start looking into this asap!

Just wanted to say that we have had to dig out a hearth for exactly the reasons given here, and we broke ours up with a hammer, chisel and crowbar (didn’t have a sledge hammer) and it was really quick to do. Shovelled rubble into bags and took to tip. Then we had a damp proof course laid under the floor and the walls were tanked (I think this is what it’s called - textured plastic lining) around the fireplace (fireplace is still there) as an extra precaution in case water was seeping through wall (stone) or down chimney.

Thank you so much @MaryLennoxsScowl - great to hear that it fixed your issue too :-) I'm getting excited that we might be able to sort this out...