I have just removed an old parquet floor and the old bitumen adhesive is left on the concrete below. It is a very thin layer but is still slightly tacky. Would it be best to remove it (if so, any ideas on the best way) or should I be looking to "skim" over the top (if so what with/how much etc.)?? I'm completly lost at the best thing to do. I've got a large area (40 sq metre) to do. Any help/ideas appreiciated!!