Some rust stains on a customer?s driveway are really just stains, and some are not. True rust stains are caused by ferrous material (such as a stone with iron content) coming into contact with oxygen and moisture. When a piece of ferrous rock is exposed to air, such as when spalling has occurred (the smooth cement surface has been worn or broken or power washed off, exposing the gravel beneath) rust will begin to form very quickly and stain the cement around this spot. This kind of rust stain can be easily identified because it appears to be originating from a single point and spreading from there in the direction water would run. The rust stain can be removed using an acid-based cleaner like Crete Clean or Pro BRC. The secret to successfully removing this kind of rust stain is to apply the acid and immediately begin to agitate the surface. Keep working the stain and rinsing the stain until it is completely rinsed clean. To prevent re-occurrence, seal the driveway with a long-lasting siloxane-based sealer like Ready Seal #30 or V-Seal.
So when is a rust stain not a rust stain? If the stain is caused by the spilling of battery acid (or similar product), it looks like a rust stain but is not. Most strong acids like battery acid will actually discolor (or ?burn?) the concrete when not neutralized within a short time of the spill. These sorts of stains tend to look like brown-orange, puddle-shaped areas on the driveway. The stain is often quite deep, and no products on the market today will satisfactorily remove this orange stain once it been on the cement for an extended amount of time. Too often, pressure washers are used to blast the surface clean when atteMPTing to remove rust stains, which amounts to peeling off a deep layer of the concrete to expose a surface that is less stained. This is not doing the customer any favors they would probably prefer the rust stain!
Sometimes fertilizer contains iron which will create a stain that looks similiar to a rust stain.
Your ability to remove a rust stain or any other stain usually depends on how old the stain is. Most successful contractors have learned to set their customers? expectations ahead of agreeing to do any job. Learning to identify the difference between these similar situations will help you educate the customer.