I recently hired a floor polisher to my best friend who had bought a load of reclaimed parquet flooring for her dining room. Traditionally parquet was glued down with thick bitumen & this was still firmly in evidence on the tiles she had purchased. Before the floor could be relaid with a modern adhesive they had to use a chisel to laboriously hardened layer of tar on the underside of every block. Unfortunately there were also marks & smears of bitumen all over the top face of the floor ruining the appearance.
Once the adhesive had firmly set we attached a 17″ red floor polishing pad to the underside of the floor polisher. PDQ was diluted 1:8 & liberally sprayed onto the floor. We then buffed 1 square meter at a time & amazingly the tar came off the floor & onto the pad. After doing a few metres the pad got sticky with tar so we flipped the pad & continued using the other side until that too got sticky. By using another pad whilst the 1st pad cooled & hardened off we found we could keep the process going.
After a couple of hours of spraying & buffing with PDQ we managed to return 600 sq feet of 100 year old parquet to it formal glory, all for less than £50.