Powdery residue on limestone despite many washings

Q. Our installer grinded off the top layer of our limestone floor and since then we have repeated powdery residue on limestone despite numerous washings and sealings/impregnatings. Why is this and can this be fixed as I don't want to have white powder on my socks every time I walk across it. Thanks!

A. It sounds like you may have what is called efflorescence. This is caused by excessive moisture which dissolves the salts in the setting bed. Over time it will disappear -- once the installation is completely dry. I would make sure that you don't have a moisture problem, otherwise it will continue to occur.  I would suggest you limit the amount of water you use for cleaning and to place some fans on the floor to dry it out.

Fred Hueston
Chief Technical Director, SurpHaces
President, Stone Forensics