Ultimate Grout Cleaner was created to clean grout in the most grueling environments- commercial kitchens, and restaurants without damaging the tile or grout. It was a difficult task because the grease was so thick and embedded deep into the grout. We tried many different formulas before we found just the right one. Our motto at Black Diamond Stoneworks is " We Make Cleaning Easy" and when you try our Ultimate Grout Cleaner you will see that we hit a home run with this product. Because this product is acid-free it will not remove calcium or water spots in your shower but it will work extremely well on the soap deposits. It will not normally etch marble but we always recommend that you do a test area first. Simply spray on the grout or tile and let stand for 1-3 minutes. Agitate with a brush to loosen embedded soil. Rinse with clean water. This product is very strong so do not use on painted surfaces. Made in the USA.