I have 6x6 old ceramic tiles around and in front of fireplace ( it is not glossy as shower tiles). Can not remove them because I will ruin mantel that I really like. What steps should I take and products (especially adhesive) should I use to put glass tiles on top?
You will have to sand or grind the old tile slightly to ruff it. Then fill the old grout lines with a Portland cement based filler/patching compound. Smooth out the surface and let it dry. You may have to sand it a little more to get it flat as can be. Then use modified thinset mortar to install your glass tile. Doesn't necessarily have to be white thinset if the backs of the glass tiles are opaqued.