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In this bedroom there is a chimney breast. There is always a large patch of damp when on the bottom left. It can be seen in front of the chimney breast and also the side. In the winter this patch expands to cover almost all of the bottom of the chimney breast. In the summer it contracts to what we see here.

We had the top of the chimney sealed so no rain and fall in. We also use hot air heater to make it go away but it stays.

I want to know if there someway to cover this part of the wall such that the patch is pushed behind and some waterproof substance is in front. Then we can just paint over the damp patch for good and live happily ever after.

enter image description here

I have tried a few things but for 3 years (since moving to this house), this patch has not gone away, it changed in size but does not go away. I am just fed up now. I want to contact the damp specialist but don't want to get ripped off.

EDIT:

This is a ground floor bedroom in a circa 1900 house. The other side of the wall is the outside of the house. There is no damp on the 1st floor room that contains the upper part of the chimney breast.

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    You will not get "happily ever after" with damp inside your wall.
    – Jasen
    Commented Aug 5 at 2:14
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    Even though the top of your chimney is closed off, then brickwork can still absorb water from the rain, and this will end up travelling down through the structure. It may help to apply a masonry sealer product to the part of the chimney which pokes up through the roof.
    – brhans
    Commented Aug 5 at 12:44
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    If you have a basement or crawlspace in that area and the floor we're looking at in this pic is not a concrete slab, then it's also likely that the moisture from the chimney has rotted the subfloor around it. I'd strongly recommend that you get underneath and take a look at the condition of the subfloor - poke a screwdriver at it and check if it's still solid.
    – brhans
    Commented Aug 5 at 12:47
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    I understand being fed up with this but if you cover it up and ignore it, you’re likely to cost yourself orders of magnitude more down the road in money and possible health impacts if you end up with mold on your hands.
    – bob
    Commented Aug 5 at 15:35
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    Your house is desperately trying to tell you to fix the underlying problem. I'd spend the time and money now to address the underlying problem sooner rather than later. Because you are looking at thousands of pounds in the future if you cover this up and pretend it isn't a problem.
    – user214437
    Commented Aug 6 at 15:50

7 Answers 7

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You MUST open the wall and find where the moisture is coming from and correct that. There may be insulation in the wall that is holding moisture. Open the wall and take a look.

Doing anything to just cover or "band aid" the problem will create larger issues.

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    @gyuunyuu, Because you are not correcting the problem. You would only be covering the problem. Covering a damp area will lead to rot and mold that can grow into a much bigger issue and possibly compromise the structure of the home.
    – RMDman
    Commented Aug 5 at 17:07
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    @gyuunyuu not being made of wood doesn't matter, bricks, mortar and plaster rot as well. If the patch has not gone away, it is not fixed. Best case scenario is that you paint over it and it soaks through the paint meaning you wasted your time. However this can lead to mould and rot which left unchecked will cause health issues, particularly respiratory. Plus when you sell, any decent surveyor would find this and it will really hit your resell price. But long term it will rot the fabric of the house and damage the chimney
    – ThaRobster
    Commented Aug 6 at 10:07
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    @gyuunyuu you may be able to seal this spot and move the mould elsewhere. Imagine you could completely seal where the water is visible, but did nothing about how it's getting into the wall. the saturated area will grow until you find a problem somewhere else. It will happen. At some point the plaster will start falling off the walls as well
    – Chris H
    Commented Aug 6 at 13:03
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    @gyuunyuu Mold will still form, even if under any covering you put on it. It will then smell, spread spores and generally be unpleasant. And Chris is right, eventually plaster will fall of the wall. The floor joists which are supported in that area will rot and fail as well. Painting any kind of product over this (even if is says Anti-Damp or Damp-B-Gone on it) will do nothing for actually getting rid of it. I get criticised a lot on here for recommending this , but if the best you can do is to paint it, you NEED to consult a (or even another) professional
    – ThaRobster
    Commented Aug 6 at 13:26
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    @ThaRobster worse then that, Black Mold could grow. Which is toxic to humans. I agree, if your solution to a damp spot is "Paint over it" then you need to hire a professional.
    – Questor
    Commented Aug 6 at 15:08
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You will notice there is a vent on that chimney breast, there should be a corresponding one at the top of the chimney stack. These are necessary to clear any naturally occurring moisture, you can test to see if it has a draw by holding a flame near it and seeing if it pulls towards the vent. A blocked vent however would not cause as much damp as you're seeing, but it would exacerbate it.

Considering that this is the base of a chimney breast I would suspect the brickwork has become impregnated with hygroscopic salts, which attract moisture and cause damp. I would in no way rule out moisture ingress, however. In any case, at a minimum you will need to remove the plaster and expose the brick, salts will appear on the surface over a period of months if they are the cause. If not and the wall remains damp you will need to investigate water ingress, likely starting at the chimney stack.

There are no quick fixes for damp and there is a lot of misinformation out there!

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  • The chimney stack has been close at the top. No rain can come inside now. I also used hot air heater of 2000W to blow air on this path for many hours. It has not gone away.
    – gyuunyuu
    Commented Aug 5 at 10:30
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    When a chimney is capped, it should also be vented, not sealed completely. This is because moisture can make its way into the chimney through the brickwork, and needs to have a path to exit. Checking the draw on the vent (visible in the photo) with an open flame will confirm if the upper vent is present and working.
    – Steven Thomson
    Commented Aug 5 at 10:34
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Two things: you said that the chimney breast is entirely covered during winter with moisture. What that means is somewhere along the way moisture is getting under your shingles on the roof and draining down to your chimney and getting under the chimney breast.

When shingles do not keep out moisture, the moisture can freeze in Winter time, and the expanding ice from moisture shingle will push it farther out from its original, tight position. And more moisture can get in. In warmer months, the moisture trickles down the Roof and comes to rest around your chimney. The same thing happens: whatever moisture can get under the fixtures there can expand those fixtures and push them out. More moisture comes in, it freezes and expands, and any fixtures are no longer tight and must be fixed and re-seated. Including shingles.

Two, you might need a vapor barrier behind the wall to further protect it.

As for a contractor, find one that will give you a free evaluation. Do this with at least three contractors. Agree on the price and get that in your contract. Make them give you a detailed estimate including labor and supplies and a total cost. Then also agree how payments work: half now, half at the end? Payments? What are you comfortable with?

Make sure all of that is in your contract

What is the time frame? The contractor might be free on certain days or mornings or evenings. What should be finished when? What would they do to protect your house during absences? If the house is damaged, say from a thunderstorm or hail, what will they do to fix the damage caused by the bad weather?

All this should be in the contract.

We had a new roof installed, and while the roofers were gone, a thunderstorm destroyed one of the walls beneath.

The contractor said he'd fix it, but they couldn't give us the same material we had. It was wall board, a material thin as cardboard. You could thumbtack posters on it, which we sometimes did. They gave us the closest material to match the room: drywall. It was a step up from the wall board my Grandpa put up after WWII.

Look around on the web to see articles about questions you should ask contractors and what should be in the contract.

Good hunting!

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As others have said, you need to find the source of the damp and fix it. You've said this is a bedroom, so it's probably upstairs. You may be able to see what's happening it by making a hole in the corresponding ceiling downstairs or by removing the flooring in this bedroom. Both of those options might be easier than opening up the fireplace. For the ceiling, if you have downlights in the right place you can sometimes remove those to give you access to the ceiling void without making a new hole.

If this is an upstairs room (or downstairs room with a suspended floor) I would be concerned about the joists if they've been exposed to moisture for years so it might be an idea to investigate further from that point of view.

You've said that the chimney is capped but water can still get in if the lead flashing is in poor condition round the base of the chimney. Adding a photo of this might help us to see the general condition of the chimney.

Is this room next to a bathroom, kitchen or utility room? Could the water be coming from another source? Are there any pipes that run in this area? Water can travel surprising distances.

If it was my wall, I'd pull up the floor, remove downlights, or use a cheap USB boroscope and poke it though the air vent holes to see if I could see where the water was coming from.

Sometimes the air vent cover is removable which will give you more access for additional lighting. There's likely to be a build up of soot and crud behind the wall. Clearing all of that out might help (it'll at least make it easier to see what's happening). Use a wet/dry shop vacuum, not your everyday one.

Good luck.

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Don't do this, if you like your house

Little children often believe that what you can't see cannot hurt you... But as adults we learn that this isn't true.

So what does this water mean? the wall behind this is wet, that wetness will cause wood to rot (leading to your house collapsing), it can cause brick/cement to degrade. It could create an environment allowing black mold to grow. black mold is toxic to humans. Even if you cannot see it, it will negatively impact your health. Basically water inside of a wall will negatively impact your house and/or health.

No good things come from trying to hide a wet wall.

What you should do instead?

Hire someone to tear apart your wall and fix this problem. Your desired solution is to hide it and hope it goes away... this means you are not qualified to fix this problem. Hire someone who is. Yes it will be expensive (Not really in the grand scheme of things, but more expensive then a paint coat), but fixing this now is cheaper then fixing it later once it becomes a real problem.

Beyond that, cannot give advice. I don't know what is causing the damp spot, My guess is some bad flashing on your chimney. And I also bet that this damp spot isn't the only one. Its just the only spot that is visible to you.

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  • I don't undesrtand "It is all made of all wood" do you mean its made completely of wood? Or something else
    – Questor
    Commented Aug 6 at 18:29
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    @Questor that's not how it typically works in a UK house of that age, pre plasterboard/drywall. Cabling is probably run through channels in a thick layer of plaster (actually multiple layers) over brick (true for both solid and cavity walls). Pipes tend to be run under the floorboards, which are separate planks and not tongue&groove, so can be lifted individually.
    – Chris H
    Commented Aug 7 at 9:24
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    ...In much more recent construction (my 90s-built house, but not 30s- and 50s-built houses I lived in before) you do have plasterboard and it's often on battens (up to about 1" thick attached to the inner masonry of a cavity wall) leaving room for cables and thin pipes. Plasterboard can also be glued directly onto the inner wall, in which case channels are cut, but that inner masonry is normally soft, some form of aerated concretre
    – Chris H
    Commented Aug 7 at 9:26
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    @ChrisH Regardless of whether there's wood in this construction, I think we can be sure it was not designed to be continually damp. I think the OP is desperately trying to rationalize covering this up which is a very bad idea.
    – JimmyJames
    Commented Aug 7 at 14:25
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    @JimmyJames yes indeed, and it's not like damp plaster is that much better than damp wood really. It's just that I don't want to OP to get confused between what's said here and what their builder says
    – Chris H
    Commented Aug 7 at 15:57
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As you’ve mentioned it’s a ground floor room, it could be rising damp.

1900’s UK houses don’t always have a damp proof course (DPC), so it is not unusual to see. If you check on the outside of the brickwork, you may be able to see a DPC (if there is one), often about 2 or 3 courses of bricks above ground level. Older houses sometimes used layers of slate in a mortar joint, often making the DPC mortar joint thicker than the other joints. (Newer houses use bituminous and then plastic DPCs in the joint.)

If your wall does have a DPC, one thing to check is that it isn’t breached outside - eg something against the wall, allowing water to bridge the DPC… soil, moss, wood, etc. Or that you don’t have water running down the wall, eg from a leak, overflow, or gutter issue.

Assuming that there isn’t a DPC, all is not lost… a specialist contractor will be able to inject a chemical DPC into the wall. DPC treatment typically also requires the removal of the plaster on the wall (often up to about 1.2 metres high) and replacement with damp resistant plaster to avoid issues with residual salts in the wall.

DPC treatment is quite common, but it has had a reputation of some “cowboy” operators in the industry. Get several quotes for the work, maybe even 6. You might find that one is significantly cheaper than others (it might be best avoided…), one significantly more expensive (ditto…), and the others quite close together; these are probably the ones you want to take more seriously. Make sure that the contractor you select is prepared to offer you an insurance backed guarantee for the work.

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  • Good point (+1), though localised to the chimney breast makes it less likely. It would be worth removing the furniture in the alcove on the left of the photo to check that.
    – Chris H
    Commented Aug 9 at 7:46
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It would be worth checking for any external access to the chimney stack. Probably not a soot door but just a hole going up into it. These are designed to keep water out but damage or (possibly external) blockage can allow water to get in.

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