Distemper used to be a popular finish, and in older houses you are quite likely to come across it when renovating or redecorating. Distemper is chalk mixed with a glue and water. The problem with it is that if it gets wet it tends to come away from the surface it is on. This means, if you paint or wallpaper over it, all your hard work could peel straight back off again.
To remove distemper, brush away any loose material on the surface and wash the area well with sugar soap or a detergent solution. Water with a small amount of wallpaper stripper can also work well. Paint the wall with a stabilising primer solution to bind any remaining distemper to the surface.
If you are trying to remove distemper from delicate plaster mouldings, wet one small area at a time and brush away the distemper with a an old toothbrush. If it remains if the finer detailing, you can use pointed wooden skewers to carefully scrape it out. Once the moulding is clear of distemper, wash it down and apply a stabilising primer.
Limewash and Cement Paints
Older houses might also contain limewash and cement paints. These will usually be no problem to paint or wallpaper over if they are in good condition. If you need to remove it, brush with a stiff-bristled brush to get rid of the majority of the paint and wipe the surface with white spirit to remove any grease. You can then stabilise the surface with a general-purpose stabilising primer.