How to remove grout stains on honed marble without causing damage?
Estimated Reading Time: 3 MinutesQ. We grouted our beautifully installed marble backsplash with a gray grout without sealing the marble first. Unfortunately, the marble—which was originally white has now turned grey. It seems the grout has discolored the surface. Is there anything I can do to restore the tile to its natural color? I wonder how much the grout color penetrated the marble, and whether it might be possible to sand off the discolored top layer or use a chemical cleaner.
The marble has a honed finish, and we haven’t tried to clean it with anything yet. We only wiped off the excess grout with a wet sponge during installation.
A. Since your marble has a honed finish and was not sealed before grouting, it’s likely that the pigment of the grout has absorbed into the surface. Honed marble is more porous than polished marble, making it especially vulnerable to staining. Here's why. Honed marble has a matte, satin-like finish that leaves the pores of the stone more open and exposed, meaning it can more easily absorb liquids, pigments, and other materials it comes into contact with, like the grout you used, for example. Without a sealer in place to act as a protective barrier, substances can quickly penetrate the surface, leading to discoloration or deep-set stains that are difficult to remove.
The goal in resolving this issue is to remove as much of the discoloration as possible without causing additional damage to the marble, especially since it has a delicate, matte finish that’s more vulnerable to both staining and surface etching. Start with the least aggressive cleaning method, which is safer for natural stone and often sufficient for lifting surface-level residue or light staining. Use a 50/50 mix of odorless ammonia and water. Wet the marble surface first, then gently scrub it with a soft-bristled brush. This may help remove surface-level grout residue or haze. Rinse thoroughly with clean water and dry with a soft towel.
If those initial steps don’t produce results, progressively stronger interventions can be considered—but always with caution, as harsher chemicals or mechanical methods carry a greater risk of damage.
If the ammonia solution doesn’t work, a stronger chemical, like a mild acid or acetone, might be needed. However, we strongly advise against trying this yourself. Marble is sensitive to acids, so there's a high risk of etching, which would dull or damage the honed finish. If you decide to do this yourself, be sure to flush the treated area with a neutralizing solution of baking soda and water. Using baking soda as a neutralizing rinse (dissolved in water) is generally safe, because it’s not being used as a scrub. Do not use baking soda as a paste or scrub directly on the marble, especially if rubbing with pressure, as it could dull or scratch the honed finish.
We strongly recommend contacting a professional stone restoration expert who can assess the damage and remove the staining using methods that, while they may cause minor surface damage, can be followed by refinishing to fully restore the marble’s appearance. Please note that if the grout has fully penetrated the marble, your PRO may advise replacing the affected tiles.
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.]