looking for suitable modern adhesive to reglue wood parquet flooring, originally stuck to concrete with black bitumastic adhesive. If possible compatible with old adhesive so that it does not have to be removed.
I use a rubberised bitumen emulsion paint - the can I have got at the moment is 'Cromaprufe' but there are lots on the market. Most builders merchants will stock it or an equivalent - may be in the roofing or waterproofing section. Daub it on pretty heavily and lay the parquet blocks into it whilst wet. It starts to harden pretty quickly so paint it on in fairly small areas (maybe 500 x 500mm at a time) and lay as you go. Use a very cheap brush and throw it away when you have finished - don't even think about trying to clean the stuff off. Same for yourself, wear latex gloves. If it gets on your skin it won't come off until the skin wears away. I have found it adheres well even when the original bitumen layer is still present though I always try to remove as much as a I can to get a good level. If it squidges up between the blocks leave it to harden completely (maybe a few days) before trying to sand the floor otherwise the abrasive will smear the sticky stuff about..... and take care about walking from the new area to adjacent since it is easy to leave black foot prints across the hallway (yes, I have done it!).
If you use something as thin as paint it "will" squeeze up between the joins.Leaving you with a costly mess to sand and get a decent finish.Plus if you use a spirit based finish it will probably make the excess paint in the joins soften and bleed,"cheapest" doesn't always work out.
I agree with Mack4 on this. F21 is as cheap as chips and is the right stuff to do the job. Why would you choose anything else?