How to lighten dark spots on the light-colored travertine?

Q. We are using travertine as the coping on our pool. I know it is a natural stone, but there are some dark spots on the light-colored travertine that really stand out. Is there a way through a chemical to lighten these spots or possibly sand? I don’t think sanding would work as well since the spots probably run deep. I’m also wondering how much the sun might lighten the spots. Any help will be appreciated. Thank you!

A. Travertine is a natural stone that commonly contains holes. To better understand the issue, it's helpful to know whether your travertine is filled or unfilled. With unfilled travertine, these holes are left open for a rustic appearance. Filled travertine has a smooth, more elegant look since the holes are filled in. Our good guess is that you prefer the latter.

The dark spots you are noticing could be caused by several factors: they might be improperly color-matched filler material, natural variations in the stone, or possibly stains.

If your travertine is filled, the dark areas might be apparent because the filler doesn’t blend well with the surrounding stone. In such cases, the filler can be removed and replaced with filler that is a better color match. A professional stone restoration contractor can perform service for you. 

If your travertine is unfilled, natural voids might appear darker than the surrounding material. Technically, in this case, there is nothing wrong with the stone. Your PRO can fill in the voids (aka, "floating") for you. 

Whether filled or unfilled, travertine has natural mineral variations that are part of the stone itself and are generally more difficult to alter. Honing will not be effective, because the darker color variations run deep, as you mentioned. However, if the dark spots are stains, you may be able to lighten them using chemical poultices and/or stone-specific cleaners. 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. Always test any product in a small, inconspicuous area first to ensure it doesn't damage the stone.

Regarding sunlight, it is true that UV exposure can have a natural lightening effect on some stone surfaces. While the sun may help reduce the contrast gradually, there's no guarantee you will see the results you want.

Given the number of potential factors involved, it would be wise to consult with a professional who can assess the situation in person, diagnose the problem, and recommend the most appropriate solution. 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.]