Spot Priming Newly Skimmed Walls

[Vander]

I have had some walls skimmed and am thinking I might need to do some spot priming before applying a mist coat. This is to deal with two things:

1. Because of the shape of the room (it's actually the hall/stairs/landing) there are quite a few corner beads. They are quite shiny which I think might indicate that the galvanising has been lost to some extent. But in any case, I'd rather be safe and am concerned that emulsion won't adhere properly.

2. There are at least a couple of small runs, and some spots, of PVA.

I have seen thinned down oil-based undercoat being recommended. Would this deal with both of these issues? And what sort of undercoat exactly? Would just a normal Dulux oil-based undercoat such as you might use for woodwork do the job. Or do I need something more specialist?

I have also seen Zinsser 123 recommended. Would this do the job? Be better or worse than the undercoat? This is acrylic - not oil-based - as I understand.

Any advice appreciated. Thanks!

 

[dcdec]

Dont put oil based undercoat on plaster.
The pva you should be able to lift/scrape off with a thin filling knife.
123 is ok over galvanised but if you think it may have been lost to some extent you may be better off with bin

 

[Vander]

Thanks for the advice. I've heard that oil based paint can react with plaster - is that why you don't recommend it?

The PVA seems to have soaked in to some extent. Will the Zinsser Bin deal with that too?

 

[dcdec]

Thats right oil based paint on bare plaster is a bad idea because the alkali salts in the plaster can bleed through it causing a soapy effect called saponification.

TBH not sure if the bin would work over the pva. I'd put the mist coat on first then look for pva'd parts of the wall, if the paint seems well adhered then i think you'd be alright, if not you could abrade with 180/240 wet n dry (dry) and then just re-prime the bare spots.