painting emulsion on old plaster

[rhinosaw]

I have a small area of wall that needs repainting , it is just the old plaster with no paint on it. is it best to primer the area first or I have read about PVA sealer, just wondered the best approach
thanks

 

[Lower]

Never use PVA as a primer for paint. There are purpose made plaster primer/sealers to stop the plaster sucking the water out of the paint, but not PVA.

A mist coat (80% matt emulsion 20% water) makes a perfectly good primer.

 

[rhinosaw]

thanks for that, as there are a few blemishes on the old plaster could I use a thin film of filler and then paint over that?

 

[JohnD]

assuming you are going to use emulsion paint, you thin the first (mist) coat with water. It will sink in and seal the surface. It should practically disappear. When dry (will not take long) you overpaint with the unthinned emulsion.

I prefer to use two mist coats. When the wall stops sucking the moisture from your brush you have done enough. You can use white matt which is cheaper than colours and will equalise the absorbency and wall colour. This will highlight to the eye any remaining defects, which you can fill or smooth and re-mist. Some fillers soften when wet so paint quickly and leave to harden. Plaster does not do that so I prefer the smallest possible pack of Easiplast or joint cement, which I find easier to use for patching and filling in thin layers.