Strange spots appeared in newly plastered hallway.

Hi this does happen with over skim from time to time , go to your local DIY store and buy some stain block in an aerosol can and spray the patches this will sort it out.

Hi, this is oil or grease under the skim, use either a stain block or an oil based paint to cover, this should sort your problem

First i would get the plasterer to come back and have a look,he may and should sort out the problem for you,failing that,it sounds to me,there may have been a substance of the walls before hand,possibly grease or similar,this should be treated before painting,something oil based,then undercoat of that.pop into local bnq or similar tell them the problem,and they should sort you out with what you need,but again the plasterer,if a decent one should do all this for you,regards paul

without seeing it its hard to tell. but it sounds like greese or silicon bleeding through. and no it wont disapeer. but might once painted. have your plasterer to pop but and have a look. n.p.m roy