My friend had a new window in his old cottage, It was put in to a stone wall and had blocks on one side and the other side was made up of new and existing bricks.He had new lintols put in aswell. The only way I could stop the damp from outside tracking back was to clad it with poly/back plaster board, and put a dpc barrier all the way around the inside of the window and a poly/back head on the lintols.Seems to have done the trick....
