I have taken up old five finger parquet in order to lay wood blocks. Underneath the old parquet is a thin layer of a black substance on the concrete presumably bitumen which was brushed on. Some of the bitumen has come away, and it is a level surface, and a friend has advised that I should put on another layer of a waterproof substance for damp purposes. There is no sign of damp in the floor of the house which is 40 years old and another suggestion was that I should leave it and lay the wood blocks down with just an adhesive layer. I have heard that if there was damp it should be allowed to come out.
Can anybody give further guidance which will be most welcome.