There is a rust mark on my new driveway. What is it and how do I fix it?
There are a multitude of causes that can result in Rust Stains on the surface of concrete. This document deals specifically with rust coloured stains created by “Ironstone” on the surface of Exposed Aggregate Concrete.
Ironstone is the common term used to describe aggregate and stone particles that are rich in iron oxide minerals. The presence of Ironstone is easily identified. In most cases, the presence of such particles near the surface of Exposed Aggregate will become apparent over a short period of time. The particles themselves are generally dark in appearance and hard to visually differentiate from other stone particles, but when the stone begins to breakdown and oxidise, a (rust coloured) leachate stream is produced that stains the surrounding concrete and marks the location of each and every ironstone particle.
The great news is, it is completely repairable and here is how to do it.
For those that would like a more detailed explanation, please download the following document.
Rust Coloured Stains on the Surface of Exposed Aggregate Concrete