Brownish Yellow Hue on Limestone Building

A common problem with limestones and some marble buildings is that they get a brownish yellow hue after cleaning. Most of the time we find that there is a high content of iron in the water used to clean the stone. Use a chelating agent in the wash water. EDTA (ethylene diamine tetra-acetic acid) or equivalent are good choices. These chelating agents keep the iron suspended in solution so that it doesn't settle on the stone and cause staining.

If the building is already discolored, try re-washing with water and a chelating agent. If this doesn’t work re-washing with a commercial rust remover may be necessary.