Damp patch next to chimney breast

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We've got an open fireplace, but haven't used it since we moved into our house about 18 months ago. The previous owner used it frequently. There's a damp patch next to our chimney breast (on the wall next to the breast), which has been growing over time, and a couple of little damp spots elsewhere on the chimney breast. The wall that the damp patch is on is the adjoining wall between us and next door (semi-detached), and the patch(es) are close to the ground, don't extend more than a meter or so up the wall. There are no problems in the rest of the chimney breast, including upstairs. We had the leading around the chimney stack mended, but we don't think there are any issues with the roof.

Various tradesmen have had a look and opinions have varied from rising damp to hygroscopic salts in the plaster. Anyone experienced similar, or either of these two problems? And how costly/difficult was it to fix them?

I want to put in a wood burning stove eventually, so need to get this sorted out, but worried about how much it's going to cost me! House is old, so damp came up on our survey, but no other obvious problems/areas of damp that we can see.

Watching with interest. We've been told the same by various (damp or salts) totally confused! Think we have both to be honest on two different walls. Damp not rising though as too high up the wall and wall is dry beneath so coming from next doors chimney. The suspected salts are in our inglenook which we've just had a wood burner installed. Has improved it 95% but still got a little crumbly bricks now and then. Would like to treat them but I don't know what with?

Salts are certainly possible, and almost par for the course of an older property with lime mortar

The other thing that springs to mind is - is the chimney pointing / leadwork failing and water coming down the chimney?

Is the chimney pot ok/rain capped?

Part of my current renovation project is requiring the leadwork on two chimneys to be redone.....

Hang fire, you've had the chimney lead redone..... how long ago?

Potential to disturb stuff and maybe even not done well?

TBH though having reread your post I think more likely the salts

how old is the house?

Have you got a water meter? Has your neighbour?

Have you got a concrete floor? Has your neighbour?

How close is the nearest radiator, sink, or other watery thing? Including the other house.

Thanks for the replies. House was built in 1910, no water meter, no concrete floors, nearest radiator is on next wall, approx 3m away. No other watery things nearby, or on the neighbours side. The lead flashing on the chimney was fixed about 6 months ago, it hasn't made the problem any better or worse, iyswim. Chimney seems ok, rain cap on etc. I don't think water is coming down the chimney as the only places we see the damp is at the bottom, next to the chimney breast, not further up the chimney breast.

Damp seems slightly worse in times of high humidity, and a dehumidifier does help a bit with stopping the spread.

If it's salts am i right in thinking the only was to get rid of it is to get new plaster on?

We just had an independent damp specialist round to look at our property that some chemical salesmen said had rising damp. The chimney breast was apparently affected.

The specialist confirmed we don't have rising damp but a condensation issue. He commented that chimney breasts can get damp as they did not build them with damp course as you would use a fire twice a day that would eradicate any moisture but nowadays with central heating the fires are hardly used.

We removed our fire and sealed the chimney breast but ours was dry.

Not sure if that helps but i would strongly advise to pay for an independent damp specialist rather than a free damp survey if you decide to get it checked out.

ok

as there is not a concrete floor, it is probably not wicking into the wall from a pipe buried in the floor.

There is a chance that the fireplace formerly had a back boiler or stove for hot water, that might still have pipes in place. You would be able to see these in the loft, there would usually be a (very old) small tank and very old pipes going down near the chimney.

As it is at low level, take up some floorboards and have a look, a sniff, and a feel. Wet bricks and rubble are easy to smell with a bit of practice. Find your airbricks and clean them out. Some might have been blocked by idiots.

As it is an internal wall, the source is likely to be either an old waterpipe, or water lying beneath the floor from high water table or faulty drains. Depending on age and quality of house, there might be bare earth or a concrete raft. The will also be builders rubble and rubbish that the builders kicked under the floor rather than carting away. If there is a lot it could be bridging the DPC. It is best cleared out as it can encourage rot.

Poke your arm down and take some photos. Preferably also your head with a powerful torch, or send an urchin down. Prevent your cat from getting down.

The source might also be next door, but you will see glistening or damp bricks in the wall, possibly with fluffy or hard deposits of dissolved minerals.