about 2 years ago i renovated a 1950's cottage. it has a cavity wall with a 60mm cavity. I put 38mm insulated slabs on the inside and the same on the ceiling and skimmed them. i also pumped the cavity with the bonded beads. Lately a problem has arisen that i can see where each fixing is (there is a dark patch on the paint) it has shown up in every room and also on the ceiling. Has anyone any advice about what caused this problem and how it can be rectified? thanks.