If you are planning on painting over an oily surface, STOP RIGHT THERE! Applying paint directly over an oily surface will be a waste of paint and time. The oil will seep through the paint no matter how many coats you apply and in some cases the paint will peel. In order to paint over an oily or stained surface, clean the oil or stain with paint thinner first, then apply an oil-based primer over it. The oil-based primer will seal out the stain underneath. After that you should be able to paint as normal without any trouble. This was the tip of the day from your RC Painters, Colorado Springs.