How do you remove old adhesive used for outdoor carpeting on a cement patio???
Carbide scraper, or a LOT of acetone.
Tough job to do. Try a tile or carpeting specialty store to see if they have special products. Just plain acetone is probably cheaper though. Cold weather will make it easier if the adhesive is still soft or sticky. Good luck.
Just occurred to me, a pressure washer might help.
Is it sticky, gummy, or hard? If it’s hard, you could try sanding it. Also, even if it doesn’t get direct Sun, the UV will help to break it down, so over time it might get better.
Are you trying to get lumps of glue off and have a smoothish surface, or do you need all glue residue completely gone?
If you just need to remove lumps of adhesive I was thinking that a heat gun a scraper would do the trick. Note that this might leave a thin smear of melted glue behind, although in the warmed state it’d probably be more susceptible to removal with an appropriate solvent.
If it’s hard and the desired result is clean concrete, perhaps sandblasting could be done? A coarse abrasive would work. Probably need a pro to do it.