Can anyone help me. I have just moved in to a 1930s detached house. I have found what looks like corrugated bitmuen sheets that have been plastered on downstairs walls. does anyone know what these are? I think they may be to solve a damp problem theough i wonder if they are just hiding the bigger problem as some of my floor joists have rotted away. should i leave them and decorate over them or take them off and get someone to plaster the wall? any help please?