How Does a Driveway Rust?

A driveway doesn't rust unless it is made of iron, which is not likely. Nevertheless, many people notice that, over time, deep red rust stains may appear on their driveways and other concrete outdoor surface. This is because of a high mineral content in the local water supply. Every time you water your lawn or wash your car with a garden hose, the water which passes over your drive leaves behind trace amounts of these minerals. Lime causes a yellowish discoloration as it builds up. In cases where the driveway turns red though, this is because small amounts of iron have built up within the rough porous surface of your concrete. Over time this iron oxidizes--in other words, it rusts, giving the impression of a rusting concrete despite the fact that the concrete itself is not rusting.

There are several methods to removing rust stains from a driveway. The first is by using a pressure washer to blast off an incredibly fine layer of concrete, taking the rust with it. The unfortunate side effect of this method is that your driveway will be worn down or eroded more quickly as the pressure is actually damaging the concrete. Another way to get rid of rust is to use a deck cleaner containing a high concentration of oxalic acid. This is an organic acid which is very powerful and, protective clothing should be worn at all times when using it. It will react with and dissolve the rust deposits while doing minimal damage to your driveway provided it is washed off soon afterward.

An alternative non-toxic method is to use a strong lemon juice solution (mixing up several packets of lemonade concentrate into a small amount of water works just as well). You just use a heavy copper wire brush with this solution to scrub out the rust. The citric acid helps break up and move the rust once you start scrubbing at it.