Which is the best to use before painting a newly plastered wall? Watered down PVA or and white undercoat paint?

Never PVA a wall that's going to be painted. The paint will just sit on top of the PVA and in time could peel off. Apply a mist coat of white or magnolia matt emulsion first ....approx 3 parts paint to 1 part water (mix well) and this will soak nicely into the plaster and give you a good base to work on. Let it dry out thoroughly before applying your topcoats. Carl.

you can paint on what is called a mist coat, this is usually done with white MATT emulsion. You can water down the white with 20 per cent water which will help the paint spread easier on the new plaster. One tip if you are painting new plaster when you cut in around the edges with a brush roller them out straight away or the brush marks will dry and show when you put the top coats on

PVA will seal your wall in a way that you do not want! Your paint won't grip as it can't penetrate the surface. Use matt emulsion (thinned) for a mist coat. Don't use vinyl matt and definitely not silk. They will seal the walls too much as they contain pva like ingredients.

neither! use a non vinyl based emulsion watered down 50/50.. Known as a mist coat.

Like above mist coat with white matt emulsion even when you'll paint walls in diff. colour - don't need cut around ceilling twice! Always work with white until you happy with surface then one coat of color - job done

Mist coat of emulsion.

Never use water based paint on the new wall plastered, Use first a MAPEI primerG or water based stabilizer for porous surfaces , then you can use any paint over this primer Trust me, forget about to mix water on vinyl matt emulsion, this is a shit primer