A curb less shower is typically used for a handicap shower, whereas without a curb to retain the water, it provides easy access for a person in a wheelchair.
There is only one critical part to this project, that your underlayment & tile within the bathroom itself is high enough to provide at least 3/4 of slope within the shower itself to provide an appropriate drainage system for the shower. Too little slope & water will flood your bath floor during each shower use.
I have personally used 3/4 underlayment, then add the 1/4" hardboard set in thin set & screwed down for the bathroom floor, then using only wood shingles & 1/4" hardboard set in thin set & screwed to provide the slope in the shower. Angle the wood shingles with the thick part to the outside of the shower & the thin part towards the drain & then cut pieces to go from 1/2 to 3/4 for the remainder, & the hardboard will slope down perfectly
Simon’s answer gets to most of it. The tile floor surface in the shower area - and preferably beyond - needs to have 1/4" per foot slope (in use, water frequently gets “kicked” beyond the actual shower footprint and it is desirable to have this water drain back to the shower area rather than puddling on the floor). To achieve this slope, the outlying floor areas will be higher than they are presently, which can create problems at the bathroom doorway and floor transition to the hallway. Traditional shower curbs contain this elevation rise and slope within the shower area and the rest of the bathroom floor can stay flat and just above the subfloor level. Adding slope to other areas of the bathroom can also create problems with toilet setting if that area needs slope due to proximity to the shower area. Then there is the waterproofing itself…we are usually required to install a continuous membrane to the entire bathroom floor (not just the shower area) and put it under 24 hour water test. This involves temporarily damming up the bathroom doorway and filling the entire room with over 2" of water (!). Depending on your inspector, they may (should) require that the entire bathroom floor have a “pre-slope” beneath the membrane and maintain a 1/4" per foot slope to ensure that any water that gets outside the shower area and through the grout will eventually find it’s way to the shower drain. Schluter and NobelSeal membrane products are great for these applications since they install nice and flat without the folds and creases of a typical PVC liner.
I use Schluter shower product that comes sloped and install nicely. the fabric that covers the shower is waterproof and adds the security you want from leaks.
