Q.: We read your recent article on cleaning concrete (November 1992, page 791) thoroughly but failed to find any recommendations on the removal of straw stains from concrete. In the past year we've had several requests for help with yellowish brown stains caused by straw, but we haven't found a good remedy.
A.: We've examined all our information sources on stain removal, some from Europe as well as the United States, and find no reference to stains caused by straw. Scrubbing with a strong detergent solution might remove the stain, particularly if the stain is fresh. This is one of the removal methods least harmful to the concrete surface.
Are stains caused by straw a common problem, or do they occur only in certain regions? We'd like to hear from readers who have had such staining and solved the problem. Also, some readers have mentioned trouble in obtaining materials like trisodium phosphate due to local environmental restrictions. We'd like to hear about other experiences with substitute materials and new problems and remedies for concrete stains.