Plaster stains

[Greenveg]

I live in a bungalow, and I have a cupboard in my hall. In between the back of the cupboard and the kitchen there is a cavity leading to the roof. For many years I had an oil fired central heating boiler in the kitchen, I now have a gas boiler. The fumes from the old boiler went into the cavity, and there was no flue liner. I have used white emulsion on the the plaster inside of the cupboard a few times, and brown stains keep showing through the plaster. Is there a sealant I can use to stop these stains appearing. I only need a small amount, would Rust-Oleum Clear Satin Multi - surface sealer 0.25L from B & Q be ok.
Regards.

 

[KenGMac]

Greenveg, good evening.
.
If it were me? I would go for Zinsser BIN or Zinsser 123

I have just used the 123 on a damp wall, one coat has stopped the flaking and no stain now visible, 1826 plaster on masonry.

This product appears in many posts on the board, I was skeptical because I have tried over time several "stain blocking" products, so far one month on all well with the 123

Worth a look? OK costly BUT?

Ken

 

[Greenveg]

Thank you for your reply. I have no doubt that Zinsser 123 is an excellent product, but at £17 for the smallest tin, I really do not want to pay this, to use a very small amount and have the rest sitting on a shelf and never get used again. I read that a solvent based undercoat paint can act as a sealant. Undercoat is better than a gloss paint as it is easier if you want to emulsion after. As I have a newly opened tin of solvent based white undercoat I thought that I would give it a try. After one coat, the stains no longer appear, and it seems to have worked.
Regards.

 

[opps]

Oil based undercoat will probably be fine. Be aggressive with brush as you apply it to ensure that any soot and paint merge.