Singerman Laboratories Rust Stain Remover for Concrete is the most effective cleaner in the marketplace for removing rust stains from concrete and natural stone. Makes the concrete or stone surface look like new. Frankly, we've been unable to find another product that actually removes rust stains from concrete, except those that are so harsh that they remove the stain by also removing the concrete. It is supplied as a white powder which is mixed with water just before application, forming a clear gel. The rust stain remover is spread thickly on the surface and left for 5 to 15 minutes. If it is a very hot dry day ensure that the gel doesn’t dry out or it will not remove the rust and may leave a film. Depending on the severity of the stain it will usually disappear without scrubbing. Very serious stain may require some brushing to move the product through the layers of rust, but do not scrub the product away, there should always be a thick gel coating. Once complete rinse the area thoroughly to prevent redisposition of the stain. Will not harm grass or other vegetation.