Unlike other types of glue, contact cement never fully cures. It dries out as the solvent evaporates, but it maintains its stickiness; that's what makes it useful for instantly bonding two surfaces to which it has been applied. You can soften contact cement by applying heat to it, which is a good thing to know if you want to remove a sheet of laminate from a countertop. Once the glue is exposed, remove it from the surface with an appropriate solvent.
What Is Contact Cement?
The main ingredient in contact cement is rubber. It may be neoprene or nitrile -- one brand used by shoemakers contains polychloroprene. The rubber is carried in a solvent cocktail that usually contains acetone and may also contain toluene, methyl ethyl ketone, naphtha, heptane and other solvents commonly found in lacquer thinner. The solvents evaporate quickly, leaving behind a rubberized coating that may harden to the touch but doesn't cure. You can always soften the coating by adding more solvent.
Procedure for Removing Old Contact Cement
If the contact cement is bonding two surfaces together, you can usually separate them by applying a combination of heat and brute force. For example, a common method to remove a plastic laminate from a countertop is to heat the laminate with a heat gun. Eventually, you can pry up a corner and because the glue has softened, you can work it off with a putty knife. Use a variation of this method to separate two pieces of leather or fabric: Heat them with a hair dryer and pull them apart.
Removing Glue Residue
Once the glue is exposed, you can clean it with a solvent:
Look at the ingredients on the can of the glue you're trying to remove, if you have it, and find a solvent that contains those ingredients -- or at least some of them. If you don't have the glue container for reference, try pure acetone or lacquer thinner. You may also be able to find a solvent specially formulated for thinning contact cement at your local hardware store.
Moisten the glue with the solvent. Although acetone and lacquer thinner are strong solvents, they won't damage fabrics, including leather and canvas, but they will dissolve some plastics. If you're trying to remove contact cement from plastic, it's safest to limit the removal methods to heat and scraping.
Wait for the glue to soften, then scrape it off hard surfaces, such as wood or concrete, with a paint scraper or wire brush. Use a toothbrush to scrub it off fabric. As you scrub and scrape, the glue will form into little balls that you can pull off with your fingers. Be patient -- removal is a tedious job that takes time.
Wipe off the residue with a clean cloth moistened with the solvent you're using. Finish up by sanding the surface -- if it's wood -- or washing it. You can use 100-grit sandpaper to get residue off of thick leather and rubber, or you can use an abrasive scrubber.
Acetone, lacquer thinner and other solvents used for thinning contact cement are noxious and flammable. Wear a mask when handling them and avoid open flames.