He didn't ''back comb'' the thinset after applying it with a notched trowel. You have to use the smooth side to smooth out the ridges, or they show through at the edges. Live with it or tear it out.

A friend of mine also said the same thing. He said that they didn't use the proper size trowel, didn't collpase the ridges, or they didn't back butter the tile. It's going to be a tedious job drilling the grout and filling the voids. I hope they just take it all out and redo it correctly.

A drill and fill is a hell of a lot easier than a tear-out.

I disagree. Look at a notched trowel. That's how many holes per square foot that you're dealing with. FAR easier to have the builder remove and start over. Or, just accept it with a discount.

You can see the same voids behind this tile in my old showroom. Because he used the notched trowel, and didn't knock down the notches with the smooth side of the trowel before installing the tile.

We accepted it and moved on. It's only really visible from a close distance. From about 3 feet, it looks fine. I think you should also assess how the tile looks from the standard seated viewing distance as well.

Classic White and Blue Kitchen from Dynasty/Omega · More Info

You'd think glass tile has been around long enough for them to know that it's see-though! Definitely trowel marks.