If concrete, would we have it scored more for traction? (There will probably be some polishing done on the rest of the flooring, but could do less in this room. Scoring will be done to control cracking, but the pattern could vary.)

I also like the look of large format slate-looking porcelain tiles that go across the floor and then up the side of the tub (you walk through the shower to get to the tub.) It is not a large room, so I'm trying to keep from chopping it up visually. But I know people usually want more grout lines in the floor for traction. Would that still be true if the tile itself had some texture?

I hope some of this makes sense-- I may have been thinking about it too much lately!

Now you can certainly do anything. If building code applies in your area and you want to be code compliant, it does make it a bit more difficult to have a code compliant "naked" concrete slab in a wet room bath and shower.

To be code compliant, believe it or not it's probably less expensive to tile the bathroom.

Pour your slab. If you want to use large format tile you need a flat slab, one flat to a certain specification. You'll have to spec it out to the concrete crew IN YOUR CONTRACT and verbally, it needs emphasis. Realize that the larger tile you use, the flatter the floor has to be.

Once the slab is in and is sufficiently cured, you can apply a topical waterproofing membrane right on the slab, then tile right on the membrane.

There are modern/industrial looking large format tiles that sort of look like concrete. Or if you go with another shade or hue, they'll blend well into that style of bathroom.

Here's a 12" by 24" charcoal for example, they also come in 24" squares.

If you want to extend the large format into the shower space too, I'd recommend looking at using a trench drain. That way your shower floor can be a single-plane, flat surface, that slopes to the trench drain. You'll not have to cut your large format to fit the inverted pyramid shape of a typical shower with a center-floor drain.

Trench drain example:

I had no idea that it would be tricky to make the concrete floor either level or waterproof. In the rest of the house, the concrete will be the finish floor, so I know we will have to make sure that everyone understands that up front. We have arranged to have a very meticulous contractor build our house, so will make sure this issue gets communicated to subs. We do have pretty strict building codes where we are.

Thanks for the tips. I did see a thread a few weeks back about another manufacturer for trench drains so at least there is some competition there now,the ones I looked at last year were insanely expensive, but yes, a much better option than the trapezoidal thing.

It is interesting how often it turns out that what seems simplest and thus less expensive actually turns out to be more labor-intensive. It is not always apparent to me going in, so it is good to hear from those "in the know."

So it is OK to use large tiles on a shower floor?

Thanks for taking the time!

Laticrete is now marketing a trench drain if that is what you were thinking of.