Bitumin is a black, tar-like substance that was historically melted and used to stick down parquet blocks to the floor. Practically all reclaimed parquet blocks have this substance attached.

The vast majority of modern floor adhesives aren't designed to bond with bitumin. Our own experience of floors laid using reclaimed blocks which haven't had the bitumin layer removed is that the solvents in glue soften the bitumen and cause it to liquefy. In the worst situations this can cause the blocks to loosen and eventually come unstuck.

Many flooring contractors would be reluctant or unwilling to lay floors with bitumin due to the high likelihood of failure during the lifetime of the floor.