How to remove hand soap stains on a bluestone countertop?

Q. I have a bathroom counter that is bluestone. Before it could be sealed a bottle of liquid hand soap was put on the surface forming a ring. Also several drops of soap were dropped on the surface causing spots. What is the best method for removing the stain. If it needs poulticing what combination of absorbent material and solvent do you recommend?

A. Bluestone is a sandstone. Although it is less porous than many limestones, which makes it more stain-resistant, it is not impervious to staining. Hand soaps often contain surfactants (derived from fatty acids) that can bind to stone surfaces. In addition, many hand soaps contain FD&C dyes. Although these are water-soluble synthetic colorants, they won't necessarily rinse off cleanly. Together, these components can adhere to or embed in the surface of bluestone.

Here are some stain removal methods you can try:

Clean the affected area with a pH-neutral or stone-safe liquid degreaser. This can dissolve and lift oily residues that may be binding dyes from the hand soap to the stone. If oil is the primary issue, this step may clean effectively and make any further work unnecessary.
If any discolorations remain, clean the affected area with an ammonia solution, about ½ cup of ammonia per gallon of water. Spot test in an inconspicuous area first. The ammonia solution will help neutralize or loosen dye molecules. NOTE: ammonia is an alkaline, which can react with stone sealers. This should not be an issue for you, since you mentioned that your bluestone had not yet been sealed. Rinse the stone thoroughly.
As you mentioned, a poultice may be necessary. Your poultice ingredients will be diatomaceous earth and the same type of degreaser used in step 1. A poultice draws the stain out of the stone over time. For detailed, step-by-step instructions on how to mix and apply a poultice correctly, check out our free Stain Management App. If the stain fades at all, that means the poultice is working. Multiple poultice applications may be necessary to completely remove the stain.
If the stains do not fade, try a different poultice mixture: diatomaceous earth and 30/40 volume hydrogen peroxide, which is much stronger than peroxide sold at drugstores and grocery stores. You can find this at a beauty supply store.

After the stains are removed, rinse the stone thoroughly and clean with a pH-neutral stone cleaner. We also recommend you contact a stone restoration contractor to apply the appropriate sealer for your stone to inhibit future staining. To find a vetted PRO in your area, visit www.surfacecarepros.com and click on Find a PRO.

ABOUT THE AUTHOR Fred Hueston is the Chief Technical Director at SurfaceCarePROS.com and Director at StoneForensics.com. He is also the author of Stone and Tile Restoration: The Manual, a comprehensive online manual for stone and tile restoration contractors. [Learn more about Fred.]