On Saturday 01 February 2014 15:28 Another Dave wrote in uk.d-i-y:

Obviously the chimney was in no fit state and tar stains and
condensation damp ruined the upstairs decorations, plaster and carpet
and the top of the corresponding downstairs wall doesn't bear looking
at.

*If* that should ever come back, here's my dad's solution (from an oil-
boiler flue that caused similar):

Cut plaster off the affected area back to brick. Sock out any tar with
tissue paper soaked in sugar soap - repeat over a week, leaving tissue
paper stuck to brick until dry. That draws some out.

Render with a 3:1 sand cement mix as the plaster "undercoat". It's less
permeable than plaster.

Seal that (he didn't, I would)

Skim plaster.



There may be more modern ways, but his way worked. Hopefully you will
not need to as it is no longer wet - or some surface sealer might be
enough (SBR might work here).


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