One easy way to solve this problem is to take a scrub pad (scotch brite works well) and put water on it and scrub the surface. If you do get any blush this will take it off and you will have no problems. This is of course assuming you use a epoxy of some quality. Again epoxy on polyester you are fine, polyester on epoxy you want to try and avoid, vinalester on epoxy is ussually ok but still not the best. That is how it has been explained to me anyhow.