Brand new plaster - water marks

[CraigG]

Hi, recently had an extension built. And the walls have been plastered. Unfortunately it rained in and I now have water marks on the bare plaster. The leak has been fixed. My plan is to paint the bare plaster with 50:50 white matt emulsion and water. Can anyone advise if I should put stain block on the water marks first (ie, on the bare plaster) or do the 50:50 emulsion:water first then put on stain block? The stain is very dark and no doubt will come through the emulsion coats. Forgetting about the water marks for a bit do I need to do a few coats of 50:50? Any advice greatly received.

 

[deandiy61]

hello Craig. Il like 20% mist coat of emulsion then stain block or undercoat.The mist coat sinks in the new plaster and grips.

 

[deandiy61]

.....

 

[Robbie uk]

As deandiy61 suggests, but a thinned down oil based undercoat is cheaper than buying stain block.