Red clay is a dominant soil type in the southern United States as well as found in other parts of the U.S. Red clay stains occur after heavy rains when water carries the clay deep into the pores of concrete, brick or stucco. Home foundation walls are often susceptible to this via splash build up, but even the simple act of walking on a concrete driveway with muddy shoes will do its damage. Power washing alone does not take the red dirt stains out.
Why are red clay stains so hard to clean from concrete and masonry? Possibly because what gives the reddish color of the dirt is iron oxide or better known as rust, which is highly insoluble in water.
We have found that the best preventative steps that can be taken are to properly landscape around your home by applying mulch beds, decorative river rock, or some other type of turf over the ground so that the clay mud doesn't splash back on your home every time it rains causing discoloration.
One solution is to hand applying an acidic cleaner to the areas through a pump sprayer, then power washing off the discoloration. This is a service that is not included in our standard house wash process but can be added on if the homeowner chooses to. It seems to me that by the time this has happened, most of the paint on the foundation is chipping or faded and needs to be re painted anyway. After we have thoroughly cleaned the house and removed any loose dirt from the surface the area is prepped to be re painted and then preventative measures can be taken to ensure this does not happen again.