Damp patches on wall

[Neverenoughbiscuits]

We have an old Victorian cottage and have issues with damp. We've had mold patches upstairs but can find no obvious cause - roof is fine, guttering redone, windows redone and new radiators put in.

In the downstairs sitting room we have 3 patches of damp on the walls which just keep coming back. They never get any worse but nothing we seem to do makes a difference. They are on an external wall. We have had the brick work repointed and are about to seal the masonry again. I paint over them with damp paint etc but nothing seems to stop it coming back. I've just repainted again with some of the damp proof paint and the paint is bubbling before it dries.

What can we do?

Could it be an old chimney that has been blocked up?

It is the wall next to where the chimney was - so one of the alcoves to the side if that makes sense.

It could be hygroscopic damp, caused by salts in and around the chimney breast. We had this in an alcove next to an old fireplace in a previous flat. Solved by hacking off the plaster and re-doing with some sort of additive that our builder put into the render/plaster. I think he may have tanked beneath the plaster but I’m not sure.

Oh ok, not that then!

I think I’d chip off the plaster to see what was underneath.

Check your chimney flashing.

Its penetrating damp, most likely if its the chimney it could be from water ingress or if its an external wall it could be the pointing.

The OP has said it's not on a chimney, the brickwork has been repointed and the masonry sealed.

Are there any window frames, air bricks, extractor fan outlets, or things like that which could not be sealed properly round the edges? Water is a bugger for entering at one point outside and appearing somewhere completely different inside.

It's not easy to tell from the picture but are your walls lined with dot and dabbed plasterboard? Because this looks a lot like moisture which has bridged across the dots and dabs.

Pointing isn't permanent of infallible, sealing masonry can also add to water trapping as the house needs to breath. A house that can't breath will attempt breath through the weekest point by cracking through the pointing to create vent routes.

I agree that I would guess it might be dot dab plastering having bridge the gap between a wet external wall and the internal plaster.

What is the other side of this wall and how old is the house? If you can. Get some pictures of the external ground level, that would be helpful, ideally near a door so it is easy to see where it is compared with the internal floor..

Could it be condensation as it’s the coldest patch in the room. What is the extract systems in your kitchen and bathroom/s like?

As someone else says check the chimney flashing. We had this on a painted brick chimney. Patches kept coming through. There were a few drips which would come down the chimney in heavy rain in the bedroom above but nothing terrible until one day it was like a tap had been turned on. Had someone out to sort out that issue which turned out to be the flashing and there's been no damp patches on the painted brick wall downstairs since.

I found a similar spot of damp in an internal wall. My DH said it was pointless ringing the insurance company. I did anyway, turned out to be £50k worth of damage due to a water leak in the floor. Moral of the story = ring the experts

I agree with Lonelycrab and think it’s salts. You can buy a damp meter kit than includes patches to test for salt although you can just lick it! I kid you not. Lick it. If it tastes like salt it’s salt. A (hopefully) permeant fix would be to take all the plaster off, seal whatever is behind the plaster, leave to dry, then replaster and paint. Alternatively, buy some cellar tanking product. Put that on the walls and then once dry, paint in a very dark colour, this will hide any further staining. This solution may last you a good few years before you need to repaint again. You can also apply Storm Shield to the outside wall as the old brickwork will be porous.