some of the doors in the house we moved into have a strange bubbling on them. It looks like a satinwoood finish. When scraped it comes off in rough strips and the wood is visible underneath. Not sure what the cause is, because it is only on part of the doors (around 20% of the total door.) I've scraped off all the affected areas and sanded them down. This has left me with areas of the door where the old coats of paint meet with the newly exposed timber areas. I was told by homebase that I needed to apply a few coats of acrylic primer/undercoat to the bare wood until it was smooth with the old paint coat. Then I can apply a top coat to the whole door. Is this right? Is it ok to paint a new coat of satinwood onto the old satinwood and the newly primed wood? is there something better than acrylic primer/undercoat?