Chimney damp caused by stove, does this sound faesible?

[yamin]

Hi

Can anyone proffer an opinion? 18 months ago we had an old chimney stack removed because the 'bricks could just be lifted off' (have since learned that this could just be the way lime mortar works but anyway). Flashings etc were repaired and the chimney stack below, which had been damp, began to dry out, albeit slowly! Fast forward 18 months e and in the summer (haha!!) we had a woodburner fitted into the old fireplace on the ground floor. This does not use the chimney as such, but does use the chimney as a space through which to route a double skinned flue. 3 months on and we've suddenly noticed the chimney is sodden again! Its half way down the chimney breast on the first floor of our two floor cottage. We have checked the roof and there does not seem to be a leak up there. A well recommended and 'old building sympathetic' builder came today and had a good look. He seems to think that the cause could be that the woodburner flue, now we're using it a lot, is, despite being twin skinned with insulation between, still getting warm enough to draw cold air into the chimney (remember, no stack) and this is condensing in the upper part of the chimney and causing the damp problem. I have read about this kind of thing before and think it sounds logical. What do you think? And as for solutions - his suggestion would be to lift a few tiles, and backfil with vermiculite to 'insulate' the twin skinned flue so that the warmth does not draw in cold air. Does that make sense? I also wonder if an air ventilation brick at cround level on the first floor in the chimney breast might help??? Either way he says we need the plaster pulling off the chimney breast in order for it to dry out properly now. Its totally sodden!

Thanks for any help and advice

Abi

 

[Gervase]

The vermiculite backfill is an excellent idea, and really should have been done when the liner was originally installed. Highly acidic tars tend to condense in the upper reachers of chimney liners if they aren't insulated, and even stainless stell, double-walled liners will rot through horribly quickly unless they're insulated. And, with the current price of chimney liners, a few sacks of vermiculite is chicken feed in comparison.
It should also solve your cold air condensation problem to boot. Go for it.
As for the plaster, if it's modern pink stuff, get it off, as once it's been sodden it will never again be fit for purpose. If it's lime, let it dry out and it will be fine.

 

[yamin]

Thanks a lot! Very reassuring to get such a positive response! I will initially go back to the man who fitted the fire I think and see if he could do this work, but either way it seems the way to go. You can't possibly tell now WHAT colour the plaster was! Its so blackened and dirty with damp. I am pretty sure its been replastered though, as has the rest of the house, in gypsum plaster. Again throughout the house this was then covered with woodchip and 4 layers of vinyl paint - just to make sure all that lovely damp was thoroughly sealed in!!!!!!! Sometimes I feel like we are living in a clingfilmed house! But we're breaking out of it.........gradually.......!

thanks again

Abi

 

[MdB]

I'm not a chimney expert (yet!) but from what I've ready your plans sound sensible to me.

 

[Penners]

Gervase is a professional, so he doesn't need my endorsement, but just to let you know that what your builder has suggested is exactly what our woodburner installer did with our chimney. The stove has a double-skin flue up inside a chimney, and the entire void between the chimney and the flue is filled with vermiculite.

Just remember - once the job has been done, you don't want to go opening up the chimney, particularly at the bottom. Otherwise you'll have an early White Christmas.

 

[yamin]

Hi

Its great to get such a strong endorsement! No quoting, no accusatory messages if it doesn't, but do you think then that this 'could' sort out this severe damp problem? Seems such a simple solution. I know theres no guarantees!

Thanks!

 

[FamilyWiggs]

How long might a liner last before being eaten away? I have a liner inside my chimney, uninsulated. Don't really want to open the top and fill with insulation - but would it be more economic to do so in the long run?

 

[Schoolmarm]

"al"

 

[Nemesis]

Alongside Grimmers and Brunny the site lost the P.Edant family too.

Are you taking up the challenge, 'marm?

 

[Pford75]

How long might a liner last before being eaten away? I have a liner inside my chimney, uninsulated. Don't really want to open the top and fill with insulation - but would it be more economic to do so in the long run?

I would suggest that the risk of an uninsulated liner can range from the relatively minor (early degradation of the liner) to the serious (major damp or leakage of fumes). Whilst it's never nice to go back and 'redo' a job...my experience is that if you don't you will always have a nagging doubt. So personally, I would bite the bullet and get it done

 

[Gervase]

How long is a piece of string? If you're burning a lot of tarry softwood with a tall stack in a cold area, you might find the liner lasts just a handful of years before it starts to look like a colander. If you're burning seasoned hardwood in an efficient stove with a good draught, then you might get a decade or so's life out of the uninsulated liner. As Pford75 says, bite the bullet and get it done. You'll save money in the long term, and have peace of mind.

 

[Schoolmarm]

No, I am not worthy.

 

[FamilyWiggs]

Schoolmarm - not sure if you are drunk or I need to be, but I'm not understanding your posts on this thread... :lol:

WRT the liner issue, does it matter if it goes colander like at the top if the smoke can still escape through the chimbly top? (will need to smoke test the chimbly I guess). Only problem I can see is when the colander "joins the dots" and 30 foot of liner comes a tumbling down...

I have a fairly robust approach to risk in life... quite happy to accept a hig risk profile...

 

[Flyfisher]

I'm pretty sure the liner goes right to the top of the chimney pot. If the liner develops holes then smoke could escape from the liner into the chimney void but would then have nowhere to go (assuming the chimney is in good condition). Having said that, I doubt that much smoke would escape from the liner because the updraught would have the effect of sucking air from the chimney void into the liner through any holes (venturi effect, I believe).

When all the holes 'join up' you'll probably hear the liner 'sag' down within the chimney, but I don't think it would tumble down unless you have a really big chimney. You'll then have a chimney liner a few feet short at the top and the smoke would be able to escape as normal. If the top of the chimney is in good condition this might be functionally OK but would probably no longer conform to building regs.

 

[Penners]

do you think then that this 'could' sort out this severe damp problem?

I'm afraid it's impossible to say. Damp is a cunning bu**er. Sometimes sorting out the obvious cause solves the problem immediately. At other times the cause can seem to be absolutely obvious, but when you eliminate it, the damp is still there.

I'm afraid the only way for you get a reliable answer to your question is to go ahead and get the work done. If it turns out that the damp problem doesn't go away, at least you've done the right thing in insulating the flue, so the money won't be wasted.

 

[FamilyWiggs]

When all the holes 'join up' you'll probably hear the liner 'sag' down within the chimney, but I don't think it would tumble down unless you have a really big chimney.

It's a big chimbly - about 9foot by 4 foot at the bottom and probably 30+ feet tall - a real "castle" job. This is why I am a bit reluctant to insulate it - would use most of the EU vermiculite mountain...

 

[Flyfisher]

Yep, I'd say that probably qualifies as a 'really big chimney'.

 

[Penners]

It's a big chimbly - about 9foot by 4 foot at the bottom and probably 30+ feet tall - a real "castle" job.

You could rent that out as student accommodation.

 

[chuckey]

If you cast in lintels or fix iron bars about 2' apart centred on the stove flue, then you can build using lightweight blocks a smaller flue to fill with vermiculite. Would be cheaper then the alternative.
There is a manor house near me which had an inglenook like yours, they walled across it and just poked the stoves rear flue outlet through the wall. Job done!
Frank

 

[Penners]

Good luck building a block wall 30ft high inside an existing chimney. Should be fun.