From the photos can anyone please diagnose what is causing these unsightly raised marks on my lower walls? They are basement walls. I normally sand them down and repaint but after a few months they reappear. Also, on the corner and another just above the skirting I did repairs a short while ago with Polyfilla only for encrustations to appear all around the borders of the filler. Polyfilla dried a funny brown colour and it seems to be seeping through now. Elsewhere on the walls the encrustations appear as small hard raised dots. The walls do not feel damp but could this be the underlying cause nonetheless? Is there anything I can do that is not too brutal, something that can hold it back for a few years at least until the next decorating round? Any advice gratefully received.