I don't have a clear picture of his intent, but I'll toss this out: As a tile backer and/or shower surround, a mud job is king. It allows the walls to be floated perfectly plumb and square, and with mesh properly embedded in and wrapped around the mud wall corners, you can actually grout your shower's inside corners instead of caulking them. It's rock solid construction. Now moving on, he mentioned "acrylic or fiberglass" for the shower floor and or portions of the walls. I translate this as a manufactured acrylic shower pan and an acrylic shower surround unit. Installing an acrylic surround over a mud job doesn't quite make sense to me. Or were those offered as two different choices? In an ideal world, I'd use the floated mud walls as the base structure. Kerdi over that would give you topical waterproofing. Tile/glass over that and you have an installation that will last for generations. An acrylic or fiberglass surround, it really depends on the quality of the unit. Lesser quality units, especially flimsy bases, can flex and crack around the drain, sometimes in a matter of years. Better quality ones can perform well for years. As to a waste of money, I don't think a mud job is a waste of money unless it's to be covered by an acrylic surround. I don't think Kerdi is a waste of money unless it's to be covered with an acrylic surround. A cheap acrylic surround can be a waste of money, a failure in the unit can cause unseen water damage, if it's flimsy and the base flexes underfoot it can give an uneasy feeling when standing in the unit. A good quality acrylic surround can give excellent value for the dollar and perform very well. But it can be installed over drywall. All totally my opinion. Could he have been describing an acrylic or fiberglass waterproofing over the mud job? I think I'm not fully understanding his intentions.

i am wondering why so few are using Terrazzo now. https://www.houzz.com/photos/cedar-park-residence-13-contemporary-bathroom-seattle-phvw-vp~92378-Park-Residence-13-modern-bathroom-seattle https://www.houzz.com/photos/berkeley-kitchen-and-bathroom-contemporary-bathroom-san-francisco-phvw-vp~3505073-Kitchen---Bathroom-contemporary-bathroom-san-francisco

I just had a new shower installed...tiled walls and floor. It is important to use small tiles for the floor so that the pitch will allow proper drainage. You don't want to use anything bigger than 2"x2" tiles. I used 1"x1" tiles. Also, my tile guy used the "Schluter System" to install the floor and drain, which is a very water-tight method of doing a tile floor. The underlayment is key to a tiled shower floor. That is what seals out water & prevents leaks...not the tile itself. The Schluter System is a substitute for the tradtional mud pan, which can grow mold & acquire other issues over time. You can google it and find a demo on their website. There are die-hard, old-school mud pan tile installers who will refuse to go in this direction, but this Schluter method is becoming increasingly more popular, especially among younger tile installers who are open to new ideas. It's much faster to install, so tile guys like that, but for the homeowner it has outstanding waterproofing capabilites, so everyone wins. I will say, if you want to go this route, it is important to find an installer with some experience installing the system. As with anything, there is a learning curve at first, so you need a person who has installed a number of them. Good luck with your decision! Wish I could send you my tile guy...he's wonderful!

I have that same bathroom. It's original to the house, which means late 60s/early 70s. I've tiled over one bathroom and am preparing to do the other one. The new tiles are so much nicer than the fiberglass pan. In our case, I don't think we could've tiled over the fiberglass pans: They weren't flat. Yeah, yeah, the new tile floor isn't completely flat either -- it slopes towards the drain -- but I don't see how it could work.