Damp Alcove

[Benjis_dad]

As part of a kitchen re-fit, an alcove has been covered in plasterboard, skimmed and painted. Now, there is black mould growing in patches on the chimney side of the alcove - I suspect the patches match up with the 'dabs' of bonding used to hold the plasterboard in place. There is no dpc on the chimney (70 yrs old). I have cleaned the patches with bleach based cleaner but they return within days.

I don't think it's condensation because the area isn't enclosed, indeed there is an external door less than 8ft opposite.

So... What is it. Any suggestions how I fix it, and do I really have to take off the plasterboard?

Thanks all

 

[Nige F]

Is the chimney vented ? It might just be soot staining coming right through to the face of the plaster....just my thoughts on it . Zinsser make exellent stain hiding paint- shellac based. Have a google for it

 

[Benjis_dad]

Is the chimney vented ? It might just be soot staining coming right through to the face of the plaster....just my thoughts on it . Zinsser make exellent stain hiding paint- shellac based. Have a google for it

The 'fireplace' is open with a stove in it - plasterboard & tiles lining it.

 

[stuart45]

Chimneys often have hygroscopic salts in the plaster, which can pass into the plasterboard when using the dot and dab. These salts attract condensation, even at a low R/H. Mould is often a sign of condensation.

Above is a photo of a wall affected by hygroscopic salts on a dot and dab system.