How do I remove the old glue residue from outdoor carpet on a cement patio?
Removing adhesive residue is normally a combination of trying different solvents available from the paint department of the local hardware store and a lot of elbow grease. It’s mostly the agitation with a brush that produces the results. I usually start with a mild solvent like mineral spirits; let it soak in for a few minutes and scrub (and scrub, and scrub) with a plastic brush. If you’re satisfied that this gets most of it up, finish with a pressure washer or garden hose and sudsy water to rinse away the residue. If mineral spirits are too weak, put on your rubber gloves and eye protection and try a product I like called Citristrip®, paint and varnish stripping gel. Read the precautions and instructions. It’s an aggressive paint stripper, so be careful not to get it on painted or plastic surfaces (like vinyl siding). Again, you’ll still have to scrub it in, even after you’ve let the active ingredients attack the glue. The manufacturer says it’s biodegradable, but I’d remove as much of the used-up glop as possible with paper towels and dispose before brooming the entire surface with a soapy water solution and rinsing with a garden hose.