Oil and grease are bond breakers. Grinding or etching over an oily driveway without first removing the contamination can spread it, drive it deeper or leave a weak interface under the new coating.
Degrease Before You Profile
Start by scraping or absorbing free oil, then use a concrete-compatible cleaner/degreaser and scrub the contaminated area. Rinse thoroughly and repeat as necessary. Rust-Oleum’s concrete-preparation instructions specifically call for spot-treating oil and grease before etching; Behr likewise requires dirt, oil and grease removal before surface preparation.
Why One Cleaning Pass May Not Be Enough
Concrete is porous. Old automotive oil can migrate below the visible surface and return after the first cleaning. A stain becoming lighter is not the same as the substrate being ready for a bond-critical coating. Repeat cleaning and test the area after it dries.
Use Water as a Screening Check
After cleaning and drying, compare how water wets the formerly contaminated area with adjacent sound concrete. Persistent beading can indicate remaining oil, sealer or another treatment. It does not identify which contaminant is present, but it tells you not to assume the preparation is finished.
Do Not Spread the Contamination
When cleaning oil, collect or control the dirty solution as practical rather than washing concentrated petroleum residue across the rest of the slab. Follow local disposal and storm-drain rules for contaminated wash water.