Sealing chimney breast before emulsioning.

[yottie]

Have just had some roof repairs to a leak which had resulted in water running down the chimney breast ending up on an inside wall. The wall has now dried out but will not take emulsion paint without ending up with a brown stain where the leaks were. In an effort to seal the (now) bare plaster I gave a coat of wallpaper paste prior to emulsion but this has not worked and the emulsion coats are starting to peel off. I intend to strip off the emulsion where necessary and use some sort of seal prior to re-doing.
Would be most grateful as to what I need to use for the job.

 

[Robbie uk]

Why on earth would you use paste before painting, the very thing you don't want to put on. Clean it all back to plaster and apply a thinned down coat of oil based undercoat. This will seal the stain.
Then mist coat the wall with thinned emulsion and let this fry, before applying further coats of your chosen emulsion paint.

 

[yottie]

Thanks for help. If I scrape off the loose then clean of with (say) sugar soap before applying the oil based ? Also if the emulsion is firm but stained is it OK to prime on top without scraping off.

 

[dcdec]

Don't agree with the oil based u/c. Oil based paint on bare plaster is a bad idea unless you use ARP first. Any damp from plaster can cause saponification.

If the leak is fixed you can just do it the normal way, thinned emulsion followed by a couple of top coats.

Forgot to say apply a stain block after the thin coat.

 

[Snacker]

This is the stuff for sealing plaster prior to painting:

http://www.amazon.co.uk/gp/product/B00EZ3ENYM?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00

I can't say I've ever used it to stop stains coming through but I'd imagine it would do so. Failing that, Zinsser do a specific stain-blocking primer:

http://www.zinsseruk.com/product/cover-stain-deep-tint/