Q. A customer asked me about sealing a brand-new garage slab to keep oil drips from penetrating the concrete, in case she decides to have the slab finish-painted in the future. Is this necessary? What product should we use?
A. Bill Palmer, former editor of Concrete Construction magazine and president of Complete Construction Consultants in Lyons, Colo., responds: Motor oil doesn't really damage concrete. But if the surface is unprotected, oil can soak easily into the concrete's pores, where it's difficult to remove.
Paint won't protect concrete from oil, but other products will. According to Denise Breard, a technical representative for sealer manufacturer Vexcon Chemicals, water-based combination stain sealers will resist motor oil but not gasoline. A better choice — one that's both gasoline- and oil-resistant — is a water-based epoxy coating. This easy-to-apply one-part epoxy doesn't require a separate primer and is designed for residential garages and basements. For the greatest chemical resistance and protection against abrasion, Breard recommends two-part water-based epoxies.
Paint doesn't adhere well to epoxy, so if you want color in your concrete floor, you'll need to stain it before applying the epoxy coating. Another option would be to use an epoxy coating with color in it. Some great colors are available, as well as decorative chips that can be mixed in with the material.
If the homeowner does get oil stains on the concrete, they should be removed as soon as possible. Here's how: First, soak up any excess on the surface with paper towels; don't rub, because that could drive the oil deeper into the concrete. Next, cover the spot with some absorbent material, like kitty litter. Keep fresh material on the stain until no more oil is being soaked up. Finally, put TSP (trisodium phosphate; available at most hardware stores) crystals over the stain, then add enough hot water to make a poultice and scrub that into the stain. Once the poultice has dried, sweep it up or rinse it off.
Depending on how deep the stain is, removing it may require repeating this process several times. If even that doesn't work, a solution of sodium hydroxide and ground limestone can be effective — but a little bit dangerous. You can also try degreasers; there are some pretty good citrus-based versions around.
