We have lived in our house now for 17 years. I am hard pressed to remember a year when the paint on our south side window sills has not peeled, which is beyond frustrating. We have tried oil based primer with oil base top coat, oil based primer with latex top coat, and last year I applied Thompsons Water Seal, waited three months, then applied oil based primer with a latex top coat. This spring, there was a bubble, a crack, and then shortly after the entire coat of paint came off in long sheets, primer and all. My wife is a very good painter--each time the surface has been sanded, thoroughly cleaned, and then painted. It never peels on the front face of the sill, nor does it peel on the vertical pieces; just the top surface. Right now it is bare as we consider our next plan of action. The side of the house is brick; the window is a double pane vinyl; the sill is pine or hemlock; and it rests on brick that is set sideways perpendicular to the wall at about a 45 degree down angle. The brick is treated with a water repellant sealer and there is a membrane barrier that was applied to the underside of the sill at the point where the sill and the brick contact. Can someone provide ideas on what to look for as the cause? Is the situation possibly too hot with the double pane window reflecting the heat and sun down on the sill baking the paint; or maybe the brick is soaking up moisture even though it is sealed and the sill is absorbing that moisture past the barrier like humidity or something? My wife is suggesting that we replace the brick that is placed at a 45 down angle with stone like granite or something and replace the sill with 5/4 cedar.