The Concrete Network

Why do car tires leave black marks on my sealed driveway? How do I avoid this and remove the existing tire marks?

Concrete Driveway
Chris Sullivan

These black tire marks could have been prevented by using a different type of sealer.

This is a phenomenon called "plastizer migration." Plastizers are polymer compounds added to rubber, glue and plastic to make them flexible. The rubber used to make car tires contains plastizers to improve traction. But when the car is driven, the tires heat up, causing the plastizers to soften and leach out of the tire. When a hot tire is parked or driven on certain types of sealers, the plastizers migrate into and discolor the sealer. The better the tire quality, the higher the quantity of plastizer—and the greater the chance for hot tire marking. Lower-quality tires are harder and contain less plastizer, so they usually result in less hot tire marking on sealers.

If switching to harder tires is not in the cards, then consider using a different type of sealer. When a sealer cures, the resins cross link, forming a sticky tangle, like a bowl of undercooked spaghetti. All sealers exhibit some degree of cross linking. The greater the cross linking, the denser the coating and the more resistant the sealer will be to hot tire marking. Most hot tire marks occur on acrylic sealers, which exhibit minimal cross linking. Using a higher-solids acrylic or a high-solids, highly cross-linked polyurethane or epoxy sealer will reduce hot tire marking greatly. These sealers form very dense films that limit or prevent plastizer migration. Striking a good balance of sealer durability and density will make all the difference when sealing driveways and garage floors.

To get rid of discoloration from hot tire marking, cleaning the surface with a concrete degreaser may be all that's needed, depending on the level of discoloration. If the discoloration has migrated deep into the sealer, you may need to loosen the affected areas with a solvent or totally remove the sealer with a chemical stripper.

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Author Chris Sullivan, technical expert and vice president of sales and marketing for ChemSystems Inc.

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