Getting oil stains out of a concrete driveway

Why detergent fails on old oil, and how a poultice gel pulls the stain back out of the slab.

Detergent lifts oil off the surface but leaves everything that has soaked in. Concrete is porous, so an old drip mark can be several millimetres deep.

A poultice gel is the answer: it sits on the stain, softens the oil and draws it upward as the gel dries. Deep stains often need two applications.