I have 4 wooden doors upstairs + Skirting that seems to have been painted with some sort of Oil based stain - do i need to sand them down before i can paint? is there another way or something i can buy to take it off......tried to paint over with emulsion but comes through as a ****y yellow colour -tried to go ver that with gloss but same again - i know i sound like a lazy git - but i only have the weekends to do it.