Marking round chimney breasts

[padstar]

I am due to have a few rooms plastered. 2 of the rooms have chimney breasts in them that have developed some dark markings on them since we painted them 6 months ago. They don't feel damp and the fact that they are on the inner skin of the breast i cant see where water would be coming from. Do you think they are safe to plaster over or do they need treating somehow first.

 

[foxhole]

Looks like you have water penetration down chimney, is it capped and in good state of repair? and vented?

 

[padstar]

Haven't been up there but am having a new roof installed after the winter so will be having the chimneys re done at the same time. If this is the cause then it should dry out fairly quickly after the chimney is redone.

 

[bobasd]

all your flues need sweeping and then venting top and bottom.
hack off all stained plaster, and 300mm beyond stains (all c/breast plaster really) and render back with a 3:1 sand and lime mix with a remedial skim finish.

 

[padstar]

all your flues need sweeping and then venting top and bottom.
hack off all stained plaster, and 300mm beyond stains (all c/breast plaster really) and render back with a 3:1 sand and lime mix with a remedial skim finish.

If they r being capped and made redundant do they need to be swept? Is the staining water penetration?

 

[bobasd]

yes.
chemical penetration from soot and lack of adequate ventilation.

 

[padstar]

yes.
chemical penetration from soot and lack of adequate ventilation.

That probably explains why the staining is to the 2 downstairs fire places (which are likely to have been used more recently) and not on the upstairs fireplaces which look like they have been redundant for decades.

Thanks for the advise. Is there any sort of sealant that blocks the chemicals that have seeped through or will removing the effected plaster be sufficient to prevent it coming back?

 

[bobasd]

all flues must be swept and vented.
just do as suggested and you will get many years of stain free decorations.