The advice given on preparation of walls & ceilings on the expert advice section on this site says you should wash down with sugar soap and water. However, my decorator says this just livens up the emulsion, by which he means softens it up, and moves around the dirt. We recently moved into a house which we now discover had not been decorated for very many years and all the paintwork is absolutely filthy. He insists it is better not to wash it down and illustrated this by pushing a rather dirty sponge with only cold water on it over a section of the ceiling. He has been decorating for over 20 yrs and thinks he knows best. When I did my own decorating, I always washed everything down with sugar soap first. Who is right about this?