from what i see, it looks like they grouted it, then wiped the grout haze off with an acid ,probably muriatic, which took out the color. I would say a color enhancer

From: Tony Warney <>
To: Stone and Tile PROS Technical Support <>
Sent: Friday, September 14, 2012 9:33 AM
Subject: [sccpartners] Slate Floor

I stripped a Slate floor about 2 years ago.  Shortly afterwards a few spots showed up in the center of a few stones.  You could wipe them off but they would come back.  I tested the Slate for moisture with a moisture meter, no moisture.  2 years later we went back and cleaned the black Slate and sealed it with an impregnator sealer.  The Slate is inside of the home.  Approximately 2 weeks later more of these dark spots showed up.  No moisture.  The floor is about 40 years old and had a wax coating on it for about 35 years that we removed.  Any ideas?

Tony Warney
Excel Stone and Tile Care

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