i have bay window in my lounge and the paint keeps lifting like a bubble just above the skirting, i have sanded it and painted it and it has done it again, the bricks on the outside appear to have a chalky look does anyone know what could be causing it? i did have a builder here doing some other work for me a couple of years ago and he took a couple of bricks out to see if anything had been dumped in the cavity and he said it looked clear. any suggestions please