Have you asked your contractor if he can attach it to studs? (He should know the spacing of the studs) Or did he put reinforcement under the shower wall when you weren't looking? Your post doesn't say if he totally forgot the grab bar, so maybe you don't have to cry yet. Good luck!

Ooh, 6 months is an eternity. Breathe in, breathe out. You'll get your grab bar installed and this ordeal will be DONE.

It has to be installed into the studs and blocking between the studs. So, the stud location has to be known without a doubt before you start drilling. Most grab bars are bigger than 32", which is the dimension that will hit two studs, and their attachment screw positions are larger than just the thin edge of a stud. Even if you hit the stud with one of the screws, the other screws won't hit the studs. They need blocking, and to be installed at a bit of an angle. Open up the shower from the other side and install that blocking. Repairing drywall is a heck of a lot easier than repairing a just finished shower wall.

What do people think of the safety of those special fasteners that flare out behind the wall, supposedly allowing the bars to be installed in a safe and strong manner? But they do require a larger hole to be drilled and maybe their own grab bar product as well.

Maybe the blocks are behind the wall. I wish you luck on this issue. Hollysprings suggestion to go from the other side of the wall is a very good solution.

A grab bar can be easily added afterwards.

If you know the location of the studs or blocking, drill your holes through the grout/tile, load the holes with sealant, then install the grab bars. Clean up any caulk squeeze out.

The only hollow wall anchors that I've relied on for the past several years are WingIt anchors.