1/2" masaic tile added above existing backlash

[Charles Mulford]

MY existing 4x4 tiled backsplash did not meet the new quartz counter I had installed. I now need to fill in the 3/4" space between the existing backsplash and the quartz countertop. I have 1/2" marble mosaic tiles to fill this space - Can I use adhesive silicone caulk to attach the tiles, and also use it as a grout to insure that it is waterproof?

[Carbidetooth]

I'm guessing you removed 1.5" of countertop and replaced with 2cm quartz?

If that's the case, I might approach it a little differently. I'd shim the top of cabinet to correct height for existing backsplash to match up, then make a piece of trim to cover the shim(s), I've even done this with a prefinished spacer that was just a little bigger than cabinet so there was a reversed stair step from cabinet to countertop overhang.

In my minds eye the insert you're planning will call attention to itself, but I'll admit to looking at this through a cabinetmaker's eyes.