We purchased 12x12 sheets of natural stone for a kitchen backsplash. After reading a Home Depot how-to book I have two questions.
1. When do we apply sealant? The book mentions that grout can stain natural stone, so apply sealant first. But it cautions that sealant shouldn't run into the cracks because it can cause the grout to fail to adhere. So should we hang, seal carefully, grout, then seal again? Or maybe seal the tiles before we even hang them?
2. There is also a brief mention that sanded grout, which is what we have, might scratch natural stone. Should we exchange for unsanded grout?
It would be better if we knew what kind of finish and texture your mosaics have, and their color would really be helpful. Most stone mosaics are either tumbled and/or matte in finish. It may not be necessary to seal them before grouting. Hard to tell without seeing/touching them and also without knowing the color of the grout. You could test a few pieces.
I rarely seal mosaic or tumbled travertine/marble, there is no one answer really. If the tiles are polished, unsanded would be the ticket, usually unsanded is what's used though. How wide are the spaces between the pieces?
TILE GUY - retired- TROY, MI - Method & Product suitability consulting.