I have a problem with damp on a spanish property which traditionally do not have DPC's. the neighbours on both sides have a similar problem. the symptoms are the rendered skim is blistering off the wall up to a height of about .9m. the problem is localised in a corner of the porch on an external wall, does anyone have experience of any succesful remedial treatment? the neighbours are tiling over the problem which I dont feel is a long term solution.