With a curbless shower, I see two issues you may be facing. If he is planning on using a traditional rubber liner, a pre-slope under the liner is required. This slope is a minimum if 1/4" per foot from the drain to the farthest wall. In this case, I assume that to be the entry. I fugure that to be about 2 3/4" higher at the entry than at the drain. The rubber or vinyl liner sits on this and a FINAL mudbed is then formed over the liner. As you can see, there will be issues with no curb and how you'll terminate the slope to a feather edge at the entry. I don't see how that can be done. The other issue is with the liner itself. I see no way to attach it to a mudbed that would have to end at a feather edge. These liners are designed to go UP the vertical walls about 6-8" and nailed into place. Having built these before, scrap the liner and use the Kerdi. It's a bulletproof install, you only need ONE mudbed as the material is bonded directly to the mud and you can generally extend the Kerdi six or eight inches into the bathroom for a bit more insurance. On one hand, yes...it's a bit more cost, but realistically, it's also a shower you'll probably never need to repair or replace. The Kerdi is under $1.40 sq/ft. Their drain will run about a hundred bucks. On the other hand, you only have the cost of one mudbed, you eleminate the vinyl liner, as Kerdi is completely waterproof, you can save by using standard drywall in the shower as opposed to cement board. This is what Schluter recommends. Bottom line is that you'll pay a little more but get a far superior shower. If your tile installer isn't comfortable or familiar with Kerdi, find one that is. Here is a link that might be useful: Kerdi Shower Handbook

"So there has to be space for a "pool" somewhere around the drain whether you use a center regular drain or a linear drain." Yes. No matter what your design, or what type of drain you install, there are pretty much two basic requirements: 1) the shower floor area needs to be sloped towards the drain at a min pitch of 1/4" per foot and a max of 1/2" per foot. 2) With the drain plugged and with a 2" standing depth of water over the drain, waterproofing needs to contain the pooled water from intruding in to the non-waterproofed areas of the house. "In the diagram I included above, if the linear drain were recessed to meet the 1/4 inch per foot of run, then it would be okay but that gets us back to seeing that a linear drain requires being recessed just like a regular drain. " Correct. For your depiction above with no changes to the drain elevation, let's say you install the drain "as is". The floor to the right of the drain that is in the shower would need to pitch to the drain at 1/4" per foot, so the floor tile at the right wall would be elevated 1-1/8" (4.5' times 1/4" per foot) above the drain. If the bathroom floor to the left of the drain was flat (as it is in the drawing), you'd have to install a 2" vertical curb at the bathroom doorway. Your wall-mounted toilet and vanity protect those items. You'd then have to waterproof the entire floor and run the waterproofing detail up the walls several inches. Let's say you want to keep your bathroom floor flat with no curb at the bathroom/bedroom door threshold. Here are a couple of examples of how you could account for the required 2" vertical. In new construction they are easy to accomplish, in remodeling maybe not so easy: 1) drop the floor in the shower 2" below the bathroom floor by shaving down or dropping the floor joists. Then reverse the direction of the floor slope in your shower so it slopes down from left-to-right. Your trench drain will now be at the right wall. With your bathroom floor "flat", you'll have a curbless entry at the bathroom/shower floor transition. The shower floor will slope down to the drain at a little under 1/2" per foot of slope, about 7/16th" per foot to achieve the 2" drop over the 4-1/2' or run. 2) Keep the drain where it is in the drawing and the slope as depicted, from right-to-left. Add a 2" curb at the shower entry. Not curbless, but a 2" curb. 3) A hybrid of the two previous examples. Add a 2" step up at the shower door entry, then have the floor slope away from the shower entry towards the right wall, with the trench drain on the right wall. You'll have a 2" step up but then the floor will slope down within the shower. One note: Even if you did a true curbless like in example #1, I extend waterproofing out of the shower and on to the bathroom floor for several feet. You need to account for not just the physical size of the potential pool of water, but also the wicking and capillary action that will pull water away from the pool.

To do what he's proposing, you cannot have a "bowl" mud slope. Take a rectangle and draw two lines from corner to corner. The resultant triangles will have to be completely flat planes that slope towards the center point where the two lines intersect (your drain). Your shower floor will have that X in it in grout from the cut tiles. This is MUCH MUCH harder to do than a bowl preslope, as it has to be sloped correctly and perfectly flat, and the intersecting X lines can be difficult to achieve uniformly for a novice. It CAN look great when done by a pro, but it can also be a slippery uneven nightmare if done by a hack who can't get it level and with tile that isn't rough enough to give your feet grip on a wet surface.

There are several sloping options that you have. I suggest that you work with your contractor and sketch up the drainage plan that you are suggesting. You might just want to install a 4' long linear drain under the shower head area with the rest of the shower area just gently sloping toward that drain............