glass mosiac backsplash

Are there concerns re: installation of glass mosiac on "used" drywall?
I plan to install a 6-inch horizontal strip of glass tile, 1-inch squares, on "used" drywall. I removed a strip of existing tile, located about 8-inches above the counter, from the counter-to-cabinet ceramic tile backsplash. The old mortar has also been removed. I also plan to use the tile manufacturer's recommended products for thin-set and grout. Thx.

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