work well on the side grout. the mortar or mastic will come off with a wood chisel or stiff putty knife using careful taps only. Its not that big of a deal.
If you use that belt sander, do not hold the tile in your hand as it will become a flying missle. You will have to build some sort of a jig to hold it and they the mess will be horrindous.
Just be careful.
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