Wierd dark circle.

[Beckmeister General]

2 years ago we took down the chimney breast in our dining room on a party wall. We then dot and dabbed on plasterboard, plastered, painted and fitted a radiator. Now a dark circle has appeared above the radiator.
Can this be damp in next doors chimney being drawn through the plasterboard adhesive by the heat of the radiator or something else?
Can anyone suggest a remedy?

 

[misterhelpful]

Could it be soot from the old brickwork bleeding through? I know it bleeds through plaster and paint but not sure about plasterboard.

 

[Beckmeister General]

To be honest this could be the case mr helpful as there was a lot of soot. I did clean it as much as I could and I pva'd it. If soot is the problem does anyone know a cure other than cutting out the offending area?

 

[WabbitPoo]

If next door's chimney is blocked off, and they haven't ventilated it top and bottom, then yes, it could well be damp coming thru.

 

[Nige F]

remedy - try Zinsser coating

 

[misterhelpful]

Ye, try Zinsser or other stain block. If damp would probably affect feel of surface.

 

[noseall]

Defo sounds like soot bleeding.

As stated try a reliable stain block.

One of the peculiarities of chimneys is the retention of hygroscopic salts within the masonry. it is always advisable to coat any chimney breast with a coat of S.B.R. slurry prior to sand cement rendering.

 

[Beckmeister General]

Thanks everyone much appreciated