Hi Glaikityin, I would give them a very light sand first to make sure that there are no bits of anything on them. Then give them a mist coat or 2 of emulsion, that is a watered down coat of emulsion with at least 25% water in it. This is because the walls will be porous and you need it to seal them before putting on finish coat. If you don't do this you will find it very hard to put emulsion on and there is a good chance it will peel off at some point. After this give them 2 coats of your finish colour and all should be well. Good luck.
Great reply from shedman. Just to say that the mist coats will also show up any slight imperfections (small pinholes etc) that can then be filled and sanded before your final coats. Good luck.
FBG40
Hi, thanks for that fbg40. I always think that if you have newly skimmed walls there is no better time to get everything right and as fbg40 says after mist coat you will see any small cracks or imperfections you may have missed. If you don't get rid of them now it will be harder to shift them when you come to decorate in the future.
In the trade we use a mist coat of contract emulsion 1st. Then,fill any holes & cracks with dry lining joint filler, not pollyfilla...(Joint filler is a much finer powder, & you can get a smoother finish on it). Sand it down, prime it with contract emulsion, then finish off with 25% thinned vinyl emulsion, followed with 1 or 2 coats of full strength.