" should he be using someone who only does waterjet mosaics? "

Do not know that that person exists but you definitely need the highly experienced high dollar tile setter. The average guy is not it.

Any suggestions for where i find hi/her in New York city?

People tend to think that because mosaics come on mesh/paper sheets that it is a breeze to just stick each sheet and cover a wall in no time. It is actually just the opposite and even worse, if the mosaic is of lower quality from a big box store.

Oceanside Glass Tile mosaic in one of my previous bathrooms. Perfectly flat. You definitely don't want lippage when using glass tile. Good quality tile and an excellent tile installer.

It is a very high quality staturio marble waterjet mosaic (expensive) i thought my contractor’s employees could handle it but im not so sure now:(.

Visit a local tile shop and ask for their best tile setter. You may want to sit down when he gives you the price, he will not be cheap. But you chose a high end tile for a high end look, and that comes at a price.

I tried that and they wouldn’t suggest anyone. Friends have made suggestions but they are all tile layers already working with a contractor. Could get complicated with our current contractor.

You have to start several decades back at the crappy framing and horrendous drywall work. That tile is the equivalent of a minimum wage slackjaw mounting 50K Chinese import rims on a 2001 rusted out 4 door Monte Carlo. Installing a $500 a square waterjet is completely disproportionate spend on top of utter dreck. Start over with different contractors. Maybe a different house. At least with this one‘s bath fully rebuilt.

And if this is a wet area, there is not 1 thing done correctly in that picture to prevent rotting out your house with water damage. Redguard is the indication of the lowest possible skill set. And doesn’t belong with white marble. Ever. https://www.ceramictilefoundation.org/homeowners-guide-to-hiring-qualified-tile-installer#chapter-1

Oh God. This is a manhattan apartment and i am sorry to report that framing and drywall are all new.

I googled this and this is what it says. what do you recommend in its place? will the red show through the thinset?

" i am sorry to report that framing and drywall are all new. "

That product is fine over cement board, not drywall if this is in a shower. And you needed top have the tile setter involved long before this, many will not want to come in now and tile over someone elses mess. They are putting the finished product on and it will only look as good as the work beneath it. You started out in the wrong direction and are now finding this out and it will cost you more because of it. Get on FB, get on the internet, and search, pick up the phone and check references. This is on you to find the right guy now.

That looks like it's being installed with mastic. Is it? It's certainly someone completely unfamiliar with a quality mosaic installation.

Its a modified quick drying thin set by laticrete.

No one with any sense uses quick set on a marble shower. Or Red Guard. That's just insane.

The quick set was recommended from Cancos where the mosaic was purchaased.

Fast drying thin ser

Set