I'm redecorating a cottage I recently moved into. When I noticed some wallpaper peeling, I found that the whole room had been previously papered with thin polystyrene sheeting, prior to applying the normal (paper) wallpaper. Why would they have done this? Initially, I wondered if it might have been to seal in dampness, but there doesn;t seem to be any significant dampness in the walls, despite being 18" thick solid stone (and 150-yr old lime mortar). The exterior of the cottage has been well rendered with modern mortar and painted with Weathershield, so if there IS any damp, I can't see where it would come from.
Any ideas?
TIA
Jake