OP,
Just a homeowner here. I totally sympathize with the struggle to find qualified tile professionals.
It took me years, and a very bad experience with an unqualified tile "pro" before I found someone who was truly qualified. It's awesome that you are asking these questions now. Perhaps you should insist that the GC hire a certified and experienced tile professional. Here are a few sites that helped me when I was struggling to find someone.
www.tile-assn.com
Click on “find a contractor” and
enter your zip code. Let the miles radius be fairly large, like 50
miles or so. The excellent tile pro that built all my bathrooms was
on that site in my area, but about 40 miles away bc he was near downtown and
I’m in a suburb.
www.ceramictilefoundation.org
This site has lots of good
information on it. I didn’t find my contractor on this site, but a
lot of people have told me that they had luck with it.
Here’s where you click to find a
contractor:
www.ceramictilefoundation.org/find-certified-tile-installers
Also, if you are a nerd
like me and you like to read, you could download a digital version of the TCNA
handbook. It’s less than $40. It’s over 600 pages, but
you don’t have to read the whole thing. Read the introduction (about
50 pages) and then read the shower chapters. You can skip all the
other chapters such as swimming pools, etc. Reading this helped me to
learn about the process and industry standards for water proofing and tile
installation; it helped me to ask more informed questions.
www.tcnatile.com/products-and-services/publications.html
Also, I went onto the Schluter, Laticrete and other company websites and watched their online tutorials so that I could understand how a shower should be built. When I finally did find a qualified pro, he told me he prefers Laticrete and he walked me through all the steps of building and waterproofing the shower. Since I had already looked at tutorials and read the TCNA manual, I knew he was explaining it exactly correctly, and it was a great relief to me.
When I helped my Dad remodel his house, that tiler chose a different product. So I went onto that company's website and read their instructions. I noticed that tile pro had skipped a step and asked him about it. They remedied the situation and moved forward. It's very helpful to read the manufacturer's instructions to inform yourself of the process.
I don't recommend looking at a lot of YouTube tiling videos, but there is one person that I looked at named Sal DiBalsi. He posts informative videos. I stopped there though bc I knew I could go down an online rabbit hole of misinformation if I wasn't careful!
While I was looking for a truly qualified tile pro, I called probably 50 people in my area and asked 1 simple question: "How do you build and waterproof a shower?" You would not believe some of the answers:
"You have to make sure the drywall is really flat, and you stick the tile on there." (drywall?)
"Waterproofing is nice, but you don't really need it."
And my favorite:
"You don't need any waterproofing because you have central AC; that will keep your shower dry."
Live wire oak is probably correct in that you might want to part ways with this contractor and hire a different crew; or insist that the GC hire a different tile sub. If they can't explain a correct waterproofing method to you, how do you know if they've ever done it? The answer "We've always done it this way, and we've never had a call-back," is not an acceptable answer. It's frustrating that we mere homeowners have to learn all this stuff and then explain it to unqualified tile "pros." When you find a truly qualified pro, they will be able to explain exactly how they build and waterproof a shower. If you have read through the TCNA, or looked at Kerdi, Laticrete and other tutorials, and looked at some of Sal's videos, this qualified pro's explanation should comport with the information you have learned. It was a great relief to me to find someone truly qualified; a huge weight of worry off my shoulders.
Best of luck to you.
Q
Open shower with a partial pony wall, no swinging/sliding door
Q