Hi Giys
Lewis glues will vary enormously but are many are difficult/impossible to remove even with solvents .
As routine I have acetone, isopropanol, white spirit, Chemspec Pog, turps, turps substitute, dichloromethane(Nitromors) and will try these using sparingly, remeber if it's not going to dissolve with a little it's not going to with a lot.
Be carefu; not to let the solvent attack the backing, particularly if bitumen.
The pile will be pretty chemically resistant.
Cheers
Doug