use a sugar soap to wash down all surfaces. hard work but worth it as you will need to eliminate the smell too. Any problem area there are many cover products that will block out the stains, Zinsser products are expensive but do the trick. good luck
You will need to buy a n emulsion without a vinyl content. Try Mcphersons eclipse from Crown Trade Centre. This will allow the walls to dry underneath and allow them to breathe. It comes in many colours. If you try to put ordinary emulsion on and the plaster is not completely dry underneath it will ...
