I know that there are 2 types of damp proof course out there - electro-osmosis and chemical, but which is the best and which should I go for? I have a 1911 terrace, and it has damp. Also, one contractor has advised I have special plaster which is anti-condensation at an extra 300 pounds. Is this worth it? What sorts of ball park prices should I expect? Help, Im a first time buyer!!!