Damp

[postitnot]

We've had our lounge painted and our previously white wall just wouldn't dry (see attched pic)

No mould or salts on the wallpaper. Now we're not sure how long it's been there for and if its the damp proof membrane or a leaky chimney!
The chimney is really hard to see as there's a sloped garage roof in the way, so roofers aren't sure if its that.
The chimney is in the garage- there was an old fire in there that we took off revealling a hole into the chimney that seems quite dry- but the airbrick in the lounge is doing nothing.

Before we get all the newly painted plaster ripped off, does anyone have any experience of this?

Maybe @PigletJohn has some ideas?

the damp patch is quite pronounced and appears to be at about fireplace position.

It does not seem to go down to the floor so I think it is not rising from the hearth.

I think quite likely rain is getting in at the top. Unless there used to be a back-boiler and there are still pipes inside that are dripping.

Get a joss-stick or a smouldering cigarette (vom). Hold it to the vent. Is the smoke drawn in? If not, your flue is not ventilated. It must be. Perhaps it is blocked at the top.

There will be a separate flue for each fire-place and chimneypot. Each of them must be ventilated top and bottom. Unless you are absolutely certain that the chimneys will never be used again, in which case you can demolish them from the top downwards and into the loft, extending the roof over the top, and leaving the flues open in the loft. This removes any future maintenance of chimneypots, flaunching or flashing.

Anyway, unscrew the vent and shine a torch in. Is there an empty space? Or a pile of rubble hidden by the builders? Is it damp? Is there actual water dripping (especially in rain)?

btw I once had a house where a pipe burst in the loft, and water squirted into a disused chimney, washing soot, grit and tarry water into the kitchen below.

Bit messy.

correction

now I look again, I see it goes right down to the skirting, so perhaps it is the hearth.

Pry the skirting off and look at the wall behind (you will have to do that sooner or later as the skirting will be damaged by damp).

Did you see the laminate floor being laid? What is underneath it? You are probably going to have to take some boards up and have a look....

in the meantime you might be able to take up some loose boards elsewhere, maybe under the stairs. See how much of a crawl space you have, and if it smells damp.

How old is the house?

Thanks piglet John!
We've opened the fireplace from the other side (the external chimney is in the garage) and it seems quite dry inside. The air brick seems to have been bricked up, but there was a vent on the garage side too.
It's very strange, seems the plaster is wet but not the brick.

We're definitely going to get rid of the chimney, just struggling to find someone to come out before 2022

take off the airbrick and have a look. Is there rubble? Is there a stone or concrete hearth?

Or is it the same fireplace in both rooms? I was expecting a separate fireplace and flue in each room.

Just saw the update- its a solid concrete floor.
Think the skirting will come off tomorrow.
House is 1930s. Garage is a bit lower than the living room, no damp in there

There's rubble in the base of the fireplace (from the garage side) same flue. We think the air brick has been sealed off (there was a gas fire on the garage side)

but is it one fireplace? Or two?

One fireplace

OK

shovel out the rubble (you can get rubble sacks at places like Wickes)

some council tips will take them. Mine charges £3 per bag, I think

Shovelling out the rubble should reduce the damp somewhat. You may notice the colour of the bricks and concrete get lighter as they dry. Take weekly photos so you can see if there is a change. If you can see a wet tidemark, draw round it with chalk so you can see if it recedes or grows. If you have a table fan or room fan (not a fan heater) you can position it to blow onto the damp bricks to increase evaporation.

if the base of the hearth is flat smooth concrete, lay a piece of clear plastic on it, and tape it down tightly. If water droplets form underneath, damp is coming from the floor.

Once it is swept clean you will probably see marks if rain is running down from above.

A 1930's house will have a dpc in the walls, but nothing under the hearth. Typically, after the brickwork for the chimneybreast had been built, it was filled with assorted builders rubble and a concrete slab poured on top.

rubble is very absorbent of damp.

once the fireplace is out of use, there is nothing to keep it warm, dry and ventilated.

Usually this can be corrected by breaking the slab and digging out the rubble, so the brickwork is exposed to the air and moisture can evaporate off the bricks. It may be two feet or more deep.

We have had some other similar cases arise here.

Thank you so much, you're so helpful.
Great advice, will get on to it tomorrow