I am currently decorating a downstairs WC that has previously been painted in a blue kitchen & bathroom paint. We have given the old walls three coats of brilliant white matt emulsion (it doesn't need K&B paint) but even on the third coat the coverage is terrible and the new paint seems to be 'sliding' off to reveal the old blue paint underneath.
Can anyone suggest why this is happening? Should I have done something to the walls before applying the new paint (in addition to washing with sugar soap etc)?
Any help gratefully received!