We recently installed honed green deoli in our bath and floors. 511 impergnator was then applied to seal the stone. The colors have changed dramatically. The honed finish is now dulled and the silvery shine is gone and many brown hues have appeared. Some of the “ostrich” markings that dotted the tiles are even gone. Can you tell us whats happened and is there anything we can do other than removal.

Thanks, Joe

Hello Joe,

The Green Deoli is a slate from India as I am sure you know. What you are describing is usually caused by the moisture in the mortar under the slate which is trying to leach our though the slate surface. I don’t believe that the sealer is the directly the cause but it is inhibiting the ‘evaporation’ of the moisture.

Most slates are a composition of muscovite, quartz, illite and some biotite, chlorite, hematite, and pyrite. That is a lot of stuff and they each have different absorption qualities. The evaporation is not a simple homogeneous wet-to-dry look transition and for this reason many choose not to seal slate at all.

I believe the setting material moisture is fighting to evaporate and the sealer is inhibiting it. This could take months to change back to the original colors but it should do so. You could try washing the floor with acetone to remove some of the sealer, but I would recommend hiring a professional to do so. The best solution is to patiently wait.

Think about this. If you could actually permanently change the look of natural stone as you described, you should patent the process.

Best wishes,
Tom Cordova

This entry was posted on Thursday, January 11th, 2007 at 3:31 pm and is filed under Questions About Slate, Regarding Other Kinds Of Stone.... You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.