Paint not sticking to drip Mark's on plaster

Hello
I have had a lot of plastering done and applied a 50/50 coat and painted a lot of the walls now. On areas that have darker patches that look like drip marks on the plaster the paint doesnt stick as well so leaves an indentation. The odd one I dont mind but 1 wall has allot so i dont want to paint it until i know what to do. I have added a pic... any ideas.? Thanks

It's probably PVA glue, which is water soluble. Plasterers like to use it on ceilings. Scrub it off with water and a scraper, it will soften when wet.

Which is why emulsion doesn't adhere well.

Hello
I have had a lot of plastering done and applied a 50/50 coat and painted a lot of the walls now. On areas that have darker patches that look like drip marks on the plaster the paint doesnt stick as well so leaves an indentation. The odd one I dont mind but 1 wall has allot so i dont want to paint it until i know what to do. I have added a pic...
Many thanks

can't see the scale but it could still be pva that has flicked off the plasterer's brush.

If you can feel the PVA splatter you will need to try and scrape them off. They can be a pig to remove sometimes. If you cannot feel them you may get away with painting over them. You will need to ensure that you do not run the roller over any given area until the paint has dried otherwise you risk pulling the paint off the splatter with the roller.

Personally I would sand all of the plaster back to remove all traces of the PVA but that is my belt and braces approach.

BTW, you should not mix the mist coat 50/50. Not only is it very messy, it may not end up killing the suction sufficiently. Always follow the instructions on the tin. I have never seen an emulsion that recommends 50/50.