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Hi! Hoping that somebody can point me in the right direction. I have noticed circular marks that look like shadows on some of my walls. It nearly looks like a trick of the light. The walls that I can see these marks on are both painted and wall papered, and go to the exterior as opposed to our adjoining neighbour. They are perfect filled in circles around the size of a saucer. Does anybody know what causes this? Thanks in advance.

Take a look at any one of our damp projects and ring the phone number for Property Repair Systems. They give free, no obligation advice and we recommend them. They will tell you what you need to do (if anything) and will also be able to supply you with anything you need to do it with but will certainly not try to sell you anything you don't need

This could be somethng known as pattern staining. If the property is an older type and there are bridges to the cavity (wall ties with mortart etc) they can form cold spots on the walls where heat can escape much quicker. The escaping heat takes tiny dirt particles with it whcih build up to black stains over a period of time.

You can often see this on external blockwork walls and though roofs that are well insulated between the rafters. In these cases the pattern staining occurs through the mortar joints and the timber rafters respecitvely.

If there is a damp issue associated with you stains, it is very likely to be this, particularly if this occurs on an exposed wall.