Is It Safe on Concrete and Asphalt?

Two surfaces people often ask about together turn out to sit at opposite ends of the scale. Xylol (xylene) is harmless to cured concrete but will attack asphalt, and the reason comes down to what each one is made of.

Concrete is a mineral: a hardened mix of cement, sand, and stone, with nothing in it for an organic solvent to dissolve. Spill xylol on a cured concrete floor and it will sit there, evaporate, and leave the slab itself unharmed. That is why xylol is sometimes used on concrete on purpose, to strip old sealers, thin certain concrete stains and cure-and-seal products, or clean up spilled coatings. The real caution is not the concrete but everything on it: xylol can lift or soften a coating or sealer sitting on top of the slab, so if the floor is painted or sealed, test first, and remember the liquid is flammable and its vapor pools in a closed room.

Asphalt is the opposite. It is held together by bitumen, a heavy petroleum product, and xylol dissolves petroleum. Put xylol on an asphalt driveway or a roofing shingle and it softens, stains, and eats into the surface, which is exactly why solvents like it are used to strip tar and asphalt off tools and skin. Keep it well away from asphalt you want to keep, and if you are cleaning tar off something, expect any asphalt underneath to suffer too. Concrete shrugs xylol off; asphalt does not.