I am having a double brick and tile house built and will be painting the interior walls myself. The builders painters have left a lot of (ceiling white) overspray on the walls below the cornices and there is up to 100mil of undercoat on the walls aroud the door frames as well as up to 20 mil of oil based full gloss. My paint supplier said I must strip off all this before I can apply the sealer/binder to the plaster wall and if I do not do so the sealer will not penetrate the plaster. Therfore the top coats will peel away from the areas not primed.
When I asked the builder about removing this excess paint he said that the painters also use a primer and the palaster under the overspray etc. is effectively already primed and all I need to do is give the area a light sand before applying the sealer. Who do I believe?