Here's the theory

This handy calculator is available at
www.johnbridge.com/vbulletin/showerfloormudcalc.cgi

Look carefully at the picture. Notice how the cement board goes down into the top layer. Et cetera.

John Bridge Tile is a wonderful site with everything you want to know about tile, and what goes under tile - like showers.

Prepping the plywood floor

There was no blocking between the studs, so I added some (minimal) blocking between the studs with 1x2s. 2x4s or 2x6s or 2x8s would have been even better.

Now would be a good time to notch the studs to allow for the liner thickness (discussed under PVC Liner)

The floor is then prepped with tarpaper and wire mesh (lath).

The tarpaper allows the wood floor to expand and contract a little. The lath (4 sq / inch or 2 sq / inch) is stapled through the tarpaper into the floor.

Pre-slope

The pre-slope is the base on which the PVC liner will sit. Mine slopes from 1" at the walls to 1/4" at the drain. The calculator will figure out your slope and how much Deck Mud you need.

Deck mud is 5 parts sand to 1 part portland cement. See John Bridge Deck Mud for more details.

There's a 90% chance your floor is not level. You should use a torpedo level and mark the studs with a Sharpie. I make marks at the proper level and then 1/4" above, since it's easy to get your marks obscured with mud.

If your floor is not level, it will require some extra mud to fill the low spots. Easier to mix a little extra now than to have to hurredly mix a little more while your floor is hardening!

PVC Liner

Water will eventually work its way through your grout and into the base of your shower. Not much on day one, but 5, 10 or 20 years later, a lot of cracks will appear in the grout. The PVC liner directs the water to the weep holes in the upper drain flange, where it can then go down the drain.

The PVC liner should go 12" up each wall, and then up, over, and down the outside of the dam. NO NAILS or STAPLES in the liner except on the top 1" inside the shower, and at the outside bottom of the dam! How the heck do you make the corners?

Simple - you make "hospital folds" (like hospital bedsheets) at two opposing walls. You need to very carefully make these folds so they're nice at tight at the corners. The folds will be three layers thick (about 3/16), and this will push the bottom 12" of your cement boards (no nails down there!) inwards, which will cause problems with your bottom courses of tile.

You should notch the corner studs where the folds will lay by 1/4" - that will provide the needed room. Ideally, you'd notch all the other studs by 1/8".. Easy enough on new construction, but not remodelling.

Dam Corners

Obviously, you've got to cut the liner to fit out over the dam. But how do you seal up the corners? You could glue strips of liner, but that's messy and doesn't work as well as the pre-fab dam corners, which are only about $1 each. Note: Home improvement stores do not always carry them.

The special glue (Oatey X-19 Shower Pan Advesive) is only sold in 8 oz cans. If you're a DIY, you will use a few swipes on the dam corners, and the rest will slowly dry up in the can sitting on your garage shelf.

Cement Board

The cement board goes on after the liner, and the bottom will later be anchored in the top layer of floor. You should keep the bottom of the cement board 1/4"-1/2" above the liner. Wooden shims will help during assembly. Use the special screws designed for cement board (1 1/4")

The cement board should not be butted against each other, but a 1/8"-1/4" gap left between each panel. Tape them with the special alkalai-resistant fiberglass tape, and mud with thinset mortar. Unlike drywall, it doesn't have to be perfect.

Why cement board? Many showers have been built with green drywall, and many have failed prematurely. Building a shower is really hard work, and you really don't want to be doing this again any time soon! Take your time, use quality materials, and your shower will last a generation or two.

Weep holes!

You must keep the weep holes from getting clogged with the top layer of cement, and provide some "voids" to allow water to find the weep holes. Pack some pea gravel above the holes, or stack some tile spacers in there.

Top layer

Metal lath is installed over the dam. The lath is only stapled on the outside bottom of the dam. It will be held against the inside by the top layer.

Finally, the top layer is poured. The top layer is 1-1/2" thick, following the same slope as the pre-slope. Again, I mark the cement board with a Sharpie.at the proper level and 1/4" inch above

That Damn Dam

The dam is made of Mortar Mix (type S). The 2x4s forming the dam were not level, so I made up for it with the mortar. The top face slopes inward 1/4" per foot - about 1/2 a bubble on your level.

This was frustrating. Finishing the top would push the sides out, and pushing the sides back in would mess up the top. So, I got the sides straight, then waited an hour or so for the mortar to start hardening, then went back and finished off the top.

This takes a real artist to do, which I'm not.

Entrance

Here's the entrance to the finished bathroom.

The room is really small, and it was hard to take pictures with a pocket digital. I really need to get a good camera and a wide-angle lens.

Shower

From the inside, you can look through the shower door, the window opposite, and the backyard scenery - like the horses in the neighbor's paddock.

Clear glass doors are passé these days - most are frosted. I had to special order the Kohler frameless door to get clear glass.

Control Panel

I wanted to put in body sprays and other squirters, but the well pump only puts out 40psig, and the plumbing was only 1/2" pipe.

Floor

It seemed a real shame to cover up that lovely shower pan, but I tried to do it nice.