Cleaning mineral deposts on marble

Q. I am wondering how to clean the marble step into our bathroom shower. It has a lot of dark brown crud -- I'm assuming it's mineral deposits -- that have built up over the years where the aluminum frame of the shower door meets the marble. Any suggestions? I've tried baking soda but that barely improves it.

A. The brown "crud" may be mineral deposits as well as rust. I would first try scraping as much of it as you can with a sharp razor blade. Once that is done get some Iron Out (available at most home centers and grocery stores) Mix the Iron Out with some water and apply it to the brown "crud" and let it sit for several hours. Rinse and repeat as necessary.

WARNING - If the marble is polished, this process may dull the finish, and you will need to have it polished.

Fred Hueston
Chief Technical Director, SurpHaces
President, Stone Forensics