What’s causing this damp?!

[Holls81]

We have a real head scratcher.

There’s a small patch of paint that peels off in the top corner of our chimney breast. (Original patch was a couple of cm.)
(downstairs in the lounge.)

I sanded the paint round the area right back to where it stops flaking off.

The plaster underneath looks darker and the metal beading down the edge is rusty in a small patch.

Now, we asked a roofer to check the flashing and he said that if it was a problem with the flashing then the problem would also be evident upstairs (which it doesn’t seem to be.)
Structural engineer came out for something else and while he was here I asked his opinion. He too had no idea other than that it could possible be a flashing issue.

We’ve had a lot of rain over the past couple of weeks and the patch doesn’t seem to have changed (ie looking wetter or drier.)

when I sanded the area, down the side in a small gap in between the cupboard and the side of the chimney breast, some wall paper came off which seemed a little damp but not mouldy. (This is not a cavity wall)

Is it possible that condensation could be causing it where the air can’t get in to the little gap and the wet wall paper, that has seemingly always been in there (we’ve lived here 10 years and haven’t ever had wallpaper) might have been holding the water and not allowing the plaster around it to dry?

I’ve heard @pigletjohn might be able
to shed some light?!

not sure what else to try!

*I should also add that the dark patch on the plaster is my greasy finger print from the other day 😫

I had this. The problem was in the loft. In the loft the chimney had been boarded around and they'd stuffed insulation around it before boarding it. So even when the roof had been 'fixed' countless times (🙄🤔)the water that was already there had no way of escaping.

I wouldn't rule out the flashing, just because the damp doesn't appear upstairs.

You can maybe rule out the flashing by inspecting it. If it's been done with cement, expect it to let water in eventually.

Oh really. That’s interesting too. Do you think it’s possible to only see signs downstairs?

The issue with the ground being too high sounds like the shingle may not be enough. Have you consider fitting a French drain around the house (basically digging a trench, putting a water permeable membrane in, a pipe with holes that can circulate air around well below ground level and then filling on top with gravel/shingle). The idea is that it lowers the later level around the house to the level of the drain. It is supposed to work if there is not much water running up to the house, but if there is you also need drain age to divert that away from the house.

A French Drain is DIY-able but would be quite a big job.

Try leaving the electric meter box off for a few days and see if it improves.

the damp patch looks like it correlates to the meter box so you might have a pocket of trapped moist air sitting in / adjacent to the small gap between the two. Might just need better airflow.

@Karmatime thanks for this. I will Google it this arvo! Not sure it’s why the problem is yet but I think it’ll have to be trial and error for now as can’t seem to get a definitive answer!

the cupboard is down and this is what it’s unearthed! It looks quite like some pictures of salt damp that I’ve seen on line but not really sure where to go from here.

some sites say that this can be present purely from fuels being burnt in the chimney for long periods before.
others say that there still has to be water coming in somewhere! Still not sure what to think or where to go from here 😫

@Karmatime when you sanded your plaster back, I don’t suppose you can remember if it was a different colour underneath?!

Hi @Holls81 - it looked a bit like yours, after light sanding it was white, then grey then that pinkish colour. I think previous owners had patched it. It didn’t look or feel damp but the worst areas were kind of spongy as I sanded. I left it bare for about a month and ran the dehumidifier every night. I’m right by the coast so everywhere is very humid so I suspect dealing with condensation is going to be an ongoing battle!

I’ve just had a little go at sanding it and the colour is lighter underneath (like the plaster is drier under the surface.)
is this how yours was?
i guess if the salts attract the condensation on the top then this would be logical?!
Talk about clutching at straws 😂

Yes I think I did find that it was lighter underneath. If you do establish that there’s no ingress of water and it’s likely to be salts then I used this to neutralise. Some of the reviews were helpful in knowing how to go about it.
Rempro 1 Litre Salt Neutraliser - Anti-Sulphate Tanking & Surface Treatment - Long Lasting Protection Against Salts in Masonry https://amzn.eu/d/860vfB2

That picture makes me think the flue is damp.

I think you said there is a liner in the chimney?

Between the liner and the brickwork, is there an airspace, or is it full of rubble?

Is the space ventilated?

And the back wall, previously hidden by the cupboard, looks like it has a strip of black mould.

Hi @PigletJohn

i believe that when the flue was lined (was a while ago so forgive me if I can’t fully remember) there was a mention that around the liner there was some sort of small stones or something put round it
for some reason or another, I remember at the time thinking that I wasn’t sure how that would work!
I think the guy said it would be beneficial for some reason but I can’t remember. Would this be bad?

when you say ‘is it ventilated’ how would it be? I’m not sure what to look for to tell you if it is or not

There are a few mould dots on the back wall. These were on the wall between where the cupboard was and where the edge of the chimney breast is. Would that be lack of ventilation in a small area? 🤷‍♀️

Sometimes the chimneys were filled with lightweight concrete poured in from the top, round the liner, sometimes a non-flammable mineral, I have an idea vermiculite and possibly pumice have been used.

Builder's rubble is often shovelled in when old fireplaces are removed, this is very bad practice and encourages damp.

If it was ventilated, there would probably be an airbrick into the chimneybreast void (not the liner) near the fireplace, and one near the top. As the liner is being used the top one would I think be outside the building.

The flue for the upstairs fireplace is separate, and also needs to be ventilated if the fireplace and the chimney pot are not both open, or partly so. The two flues will run next to each other, you would probably have to see which pot smokes to work out which is on the right (damp) side.

BTW you could drill into the damp patch, and see if the brickwork gets wetter or dryer as you go deeper. Scrape out a bit of dust from the back of the hole, or poke a bit of wood into it.

It indicates damp. Some people say it shows condensation but I'm not convinced this is the only cause. It is also found near long-term leaks.

Lack of ventilation does not exactly cause damp, but ventilation removes water by evaporation, so damp is worse when not ventilated away.

So the shingle round the liner would be a bad thing? I’m sure he said it would be a good thing. Why would you even bother doing it at all?! Doesn’t seem to make any sense. Just making more work for himself! 🙄
ah, I see re flues and working out sides. I’ll check which pot smokes when we light it.
no sign of air bricks.

when I sanded the plaster earlier it was definitely a lighter colour underneath than on the surface. What would this mean?

you’re so clever- this is much appreciated

I don't know the significance of colour change. Your brown plaster looks like damp modern gypsum, it usually turns pale pink when dry, but sometimes stays brown in patches if overpolished. It might have surface damp, or it might have been feathered out over old plaster or filler. Scrape a bit off and look at colour when wet and when dry. You can also recognise it by the smell but I don't know how to describe it

Old lime plaster is usually off-white and very thick. It is quite strong.

Polyfilla is bright white and goes soft when wet.

BTW in some coastal areas beach sand has been used. It is full of salt and always damp. I think it has to be hacked off, and/or drylined over.

My first thought was chimney salts too, old house and similar problem here. Haven't solved it, we just keep painting over it.

Oh really? Does it look like this? Do you have water coming in which has caused it?

@PigletJohn is there another way I can ventilate if no air brick? also, how would I get the stones out of the chimney?!

Chimney stack was long gone so no source of water that way, the walls just have life of their own! Damp weather /condensation seems to affect it, we use a dehumidifier now and then to suck it out.

You wouldn't normally remove the chimney-liners filling.

If they are competent it would be one of the lightweight materials. If not it might be builders rubble, and this holds damp, either next to ground level where it absorbs from the ground (old hearths have no DPM) but this does not seem to apply in your case, because from what little I can see, the fireplace seems to have been opened up and you have not mentioned damp near the floor

Or higher where a chimneystack or upstairs fireplace has been removed and the builders threw rubble into the hole to save themselves the trouble of carrying it away. I do not know if that is a possibility in your case.

Show us some pics of the outside face of that wall, please.

We still have the fireplace upstairs but it’s not used.
The company we used to fit the flue lining and check out the burner came highly recommended with hundreds of excellent local reviews so I’m hoping they were competent.
I’m currently at work. Will post a pic of side of wall/chimney once I’m home.

thanks, once again!