Damp patch on chimney breast in bedroom

[Tobiasisno1]

Hi everybody. The above problem is proving difficult to get to the bottom of, and I'd appreciate your thoughts. The patch extends from the ceiling to about halfway down the wall. It's only on the flue for the groundfloor room below and is definitely worse after rain. The flue from the bedroom fireplace is fine.

I've had builders on the roof looking at the flashing and pointing and these appear ok. The chimney is topped with a pot which is covered at the top but is open on 2 sides for 6 inches down as the intention is to use the fireplace eventually. I've read the various "damp chimney" posts but am none the wiser really. The house is over 100 yrs old and the bricks of pretty poor quality. The chiney has been swept.

Would it be worth trying a waterproofer on the brickwork? Any other suggestions? If I can't identify the cause what is best to apply in the room to stop the damp spoiling the decoration-the whole room is down to the brickwork at the moment for replastering.

All replies very much appreciated.

Keith

 

[JohnD]

is the chimnney ventilated at the bottom, with a through-flow of air?

is the damp patch clean or brown? how does it smell?

have you looked at the chimney in the loft space on a rainy day?

 

[Tobiasisno1]

is the chimnney ventilated at the bottom, with a through-flow of air?

is the damp patch clean or brown? how does it smell?

have you looked at the chimney in the loft space on a rainy day?

Is it ventilated?-yes fireplace is open at the bottom.
How does it smell?-Don't know, haven't had a good sniff, but the room doesn't smell. I'll get up close and personal with it tonight!
Loft space-not on a rainy day but builder had a look in the loft and didn't think it was damp up there but I'll question him again.

Plasterer made the point that there was no mould on the ceiling plaster, is that of any significance? The patch was there when we looked at the house, and has remained there whilst I've been working on it during the past year, when we've had a lot of rain and there's been no heat in the house.

Thanks for your interest.

Keith

 

[banter2]

whatever the replastering method you are using for the room is fine, may i suggest dry line and skim. but on the chimney breast face use sand and cement render with a liquid waterproofer in the mix, after skiming no damp or staining will ever strike through

 

[Tobiasisno1]

whatever the replastering method you are using for the room is fine, may i suggest dry line and skim. but on the chimney breast face use sand and cement render with a liquid waterproofer in the mix, after skiming no damp or staining will ever strike through

Thanks,I think that's what I'll end up doing but I would like to get to the bottom of the problem to be sure of a permanent cure. We shall be dry linining the rest of the room using insulation backed board for the external walls.

Keith

 

[JohnD]

for interest, tape a piece of clear plastic tightly to the wall. If the moisture is on the wall side, it is penetrating through the brickwork, but if it forms on the room side, it is condensation.

The cures are quite different.

 

[Tobiasisno1]

for interest, tape a piece of clear plastic tightly to the wall. If the moisture is on the wall side, it is penetrating through the brickwork, but if it forms on the room side, it is condensation.

The cures are quite different.

That's an interesting idea which I'll try. However if it were a condensation problem why would problem only be apparent over the 1 flue-the flue up from the fireplace in the bedroom is not affected.

Thanks
Keith

 

[JohnD]

aha

you said the chimney was ventilated from the fireplace.

But it is not the fireplace flue that is wet?

Is the other flue ventilated?

 

[Tobiasisno1]

aha

you said the chimney was ventilated from the fireplace.

But it is not the fireplace flue that is wet?

Is the other flue ventilated?

Sorry if I've not been clear. The damp is apparent across only the half of the chimney breast which corresponds to the flue serving the downstairs room below the beadroom. The half of the chimney breast corresponding to the flue for the bedroom itself is dry. This flue has a different pot at the top- 1 with a "lid" with round holes around the side-the builder's merchant described it as an "elephant's foot because of its shape. The flue from downstairs has a pot on it which is more open cos the intention is to have an open fire in the fireplace downstairs, so it is of course ventilated.

Keith

 

[JohnD]

OK

so the damp flue is the one that is open at the top, and open into a fireplace at the bottom.

It may be worth checking with a bit of smoky newspaper that there is a good flow up it, and it has not been blocked by birds nest, fallen mortar etc. A ventilated flue usually keeps itself dry.

And the flashing and pointing appear to be OK, they would have been the suspects.

 

[Tobiasisno1]

OK

so the damp flue is the one that is open at the top, and open into a fireplace at the bottom.

It may be worth checking with a bit of smoky newspaper that there is a good flow up it, and it has not been blocked by birds nest, fallen mortar etc. A ventilated flue usually keeps itself dry.

And the flashing and pointing appear to be OK, they would have been the suspects.

I'll try that as well but the chimney was swept about a year ago, although it is of course possible that something has got in there in the meantime.

Essentially the problem is as bad now as it was when we bought the house despite fitting the chimney pot, and examining the flashing/pointing.
I'm not a builder, so don't have specialist knowledge/years of experience, but do pride myself on being able to solve most problems by a process of elimination or trial and error, but I'm running out of things to eliminate!

Have you any experience/knowledge of paint-on waterproofing of brickwork, cos that's the only thing I can think to try now.

Keith

 

[Symptoms]

Tobias - you say you have one pot replaced when you bought the house. Did the builder who installed it remove both pots, cleaned-up the top of the stack (including repointing), then re-set the roots of both pots in mortar, then re-flaunched both pots (the flaunching is the hump of mortar around the base of the pots to allow water run-off)? I bet that he only chopped out one pot and ½ the flaunching, put the new pot in and 'buttered-up' that bit of flaunching to the existing stuff. A crack has now developed at this interface allowing rainwater to dribble down the inside of the chimney thus causing your damp patch. This is a common problem.

Can you get up there and look?

Anyway the cure is to re-flaunch, fix/replace any damaged bricks on the oversailing courses (the bits that stick out at the top of the stack below the flaunching to create a water drip), replace cracked bricks, re-point. Old flashing can often appear OK but can develop cracks/breaks which will let through water, This is especially true on hipped roofs that meet stacks (in the valley behind the stack); this area is also prone to debris build-up which can cause a moisture bridge.

Chimney stacks take a terrible pounding and are usually in poorer condition than other brickwork if not maintained.

 

[Tobiasisno1]

Thanks for your input Symptoms.

I'm not particularly keen on taking a look myself although I suppose that's the only way of being absolutely sure of the condition of the chimney. However I'm reasonably confident in the builder who has been up there recently as I've had various jobs done by him in the last 20+ years with no serious problems and he's just finished a fairly big job at the property (£40k's worth).

With regard to the pots both were fitted at the same time by the chap who works full time with the builder usually but also does small jobs on his own. Again I've known him as a friend for 20 years or more. Prior to these pots being put up there the chimney was open at the top so it was just a case positioning the pots and flaunching up round them both at the same time. The new pots don't seem to have made the problem better or worse, which is why I'm inclined to think the cause of the problem lies elsewhere.

I think my next step is to remove a brick in the bedroom and take a look inside the chimney when it rains (shouldn't have to wait long!) and see what the inside is like. I'll report back if I find anything interesting.

Thanks again

Keith

The roof was retiled some years ago before we bought the house and the flashing redone then I presume