damp chimney breast after fitting register plate

[calvert]

I've had a log burner professionally fitted in an existing big victorian fireplace. They fitted a register plate, lined the chimney with twinwall flue and put vermiculite in the space. Ever since, there is a damp patch on one side of the fireplace about level with the register plate. Can someone tell me the cause please and even better, a cure? Thanks.

 

[r896neo]

how long since it was installed? I would take it up with the fitter.

 

[calvert]

My view is that if he knew the problem he wouldnt have caused it in the first place.

 

[r896neo]

I'm not sure what you mean by that exactly but as i asked before how long ago was it fitted?

 

[calvert]

It was fitted at the beginning of summer. There was never any damp on the breast before so I am guessing that it must be as a result of the work.

 

[Nige F]

register plate. Can someone tell me the cause please and even better, a cure? Thanks.

Lack of ventilation up the flue - bricks full of hygroscopic salts from the soot of open fires - only way out now is through the bricks into room . If He knew what might happen he might have told you and you might not have had the stove fitted

 

[calvert]

Good theory. I don't think its salts in the stone work, there is no powdery stuff but it is actually wet. Suppose I cut a vent hole in one side of the register plate and get rid of the vermiculite? OK so I'd loose some heat but I'd rather have a dry wall.

 

[Nige F]

If it`s vermiculite and cement - you could do that . But if it`s plain then it`ll just pour out until the whole flue is empty . I don`t know if it needs to be mixed with cement under normal install conditions - maybe a HETAS engineer or the original fitter could tell you. Stone not brick - out of my depth now

 

[calvert]

I could clear up the mess OK but is the vermiculite just there for insulation as per building regs?

 

[Nige F]

To a point it is , but you might then find the liner isn`t staying hot enough - and get condensation/tar problems on the inside of it . I suppose worse case scenario is you compromise the life of the liner and have to spend out on a new one sooner Could be a can of worms - if it was my house I`d get several opinions and even consider covering the patch on the face of the chimney with a false wall .

 

[calvert]

Thanks for your replyNige. I did wonder about the false wall idea myself. Isnt the double skin flue insulated enough to stop condensation?.

 

[Nige F]

Not enough for a woodburning closed stove - the flue gasses are relatively cool and slow moving, you need well seasoned wood . You didn`t get much bother with open flues because there was so much air and heat lost up them

 

[calvert]

Hmm. That gets me thinking, I wonder if they actually put the vermiculite in then? I presume the condensation forms on the outside of the flue (soory but I dont know anything about this). would the be enough to sit on the register plate and just seep round in th eplaster?

 

[jeds]

It could be condensation off of a poorly insulated flue. But it could also be rainwater tracking down the flue liner. Are you in a position to check the flaunching and sealing on top of the chimney.

 

[calvert]

sorry for the delay, computer packed up! unfortunately its too high for my ladder to reach to check the flaunching. We have just had 3 days of very high winds and today the wall has dried out, the first time it hasnt been actually damp to the touch for months. The fire has been used every day so now i'm thinking that it must be water getting in rather than condensation. Should the flue liners terminate with a flat plate to cover the chimney and then have the pot cemented on top can anyone tell me please? thanks.