Building a traditional shower base
Photo 1: Draw the floor
Draw the outline of the shower floor on the subfloor to use as a pattern for setting the mortar forms. Nail an 8d nail next to the wall and strike a 65-in. arc for the curved form board.
Photo 2: Confirm the layout
Lay out the shower on the subfloor using your finish materials—in this case, tile and glass block—to help define its size and shape.
These days, if you want to put in a shower, you can just go to a home center and pick up a fiberglass unit. Before that was possible, pros had to build a shower pan base by mixing and applying mortar, troweling it flat, and laying ceramic tile.
Although fiberglass units make the job quick and easy, they lack the elegance of a handcrafted mortar and tile floor. So if you’d like to install a tile shower and are willing to build your own shower pan, you’ll be able to tile it to match the walls. And with a mortar and tile floor, your shower can be any shape. (For instance, see How to Install a Glass Block Shower.) In fact, no matter what its shape, if the shower you have in mind doesn’t conform to the rigid size requirements of a manufactured base, a mortar floor may be your only alternative.
You’ll find that the cost of the materials used in a hand-crafted base is roughly the same as the cost of a comparably sized fiberglass pan. The downside is that instead of just plugging a manufactured unit into the opening, you’ll have to do a lot more work. You’ll need a couple of days to form and tamp in two layers of mortar, deal with some tricky vinyl membrane liner work and then install the tile. This isn’t a project for winging it or taking shortcuts. A poorly installed base will leak, and the only correct way to fix a poor installation is to rip out not only the base but also the shower walls.
Don’t let the complicated shower floor featured in this story scare you (the floor is designed to complement the story on How to Install a Glass Block Shower). The fundamental techniques are the same for even the simplest shower, so pay attention—even if you’re installing a shower the size of a phone booth.
The professional who helped us could have completed our floor in less than a day with an assistant if we hadn’t slowed him down by taking these photos. If you have experience with cement and some basic trowel skills, you should be able to do almost any size shower floor in less than two days, excluding tile work.
This shower weighs upward of 1,000 lbs., or about the same as a spa with a couple of people in it! If you live in an older home with 2×6 or 2×8 floor joists, you may need to beef up the floor with some beams or extra floor joists. If you’re unsure, consult a building inspector. And if you have a house that was built in the ’70s, it could have a 5/8-in. particleboard underlayment that will need to be removed before starting.
Buy your materials at a tile supply house
Photo 3: Open the walls
Cut the drywall so that the seam of the drywall and cement board falls halfway behind the glass block, and install backers in the stud wall to support the cement board/drywall seam. Cut the top of the drywall at 6 ft. 2 in. above the plywood floor to allow for the slope fill and two layers of 3-ft. wide cement board.
Photo 4: Form the curve
Toe-nail 2×6 blocking at the base of shower on interior walls to support the vinyl liner. Toe-screw 2×4 blocks to the subfloor every 12 in. and 1/2 in. away from the line to allow for the thickness of the hardboard siding. Rip the siding to 3-1/2 in. and screw it to the backside of the blocks for curved curbs. Toe-screw 2x4s for straight curbs and cut off the excess hardboard after forming (toe screws are easier to remove after the mortar work is done). Nail in permanent 1-in. thick screed boards against walls.
You can run all over town trying to round up the special tools and materials you’ll need. Save aggravation and get it all at a store that specializes in ceramic tile. It’ll not only have everything on hand, but also help calculate how much of everything you’ll need. Bring in a scale drawing of the shower to make the job easier.
Here are the basic materials:
- An 80-lb. bag of ceramic floor mix for every 4 to 5 sq. ft. of shower floor area. (Buy extra and return unopened bags.)
- CPE membrane (the vinyl liner) 12 in. longer and wider than your shower. The maximum width available is 6 ft. If you need to go wider, you’ll need to consult the manufacturer’s instructions for lapping and welding seams.
- Enough galvanized expanded metal lath to cover the floor, with an extra 12-in. width to handle any curbs.
- Some hot-dipped 1-1/4 in. roofing nails to fasten the membrane and the cement board.
- A roll of fiberglass tape to tape the seams of the cement board. Be sure to buy the heavy-duty type for use with thinset mortar, not the light, self-adhesive type used for taping drywall.
- Enough 2×4 material to form the curbs, and enough smooth 12-in. hardboard siding ripped down to 3-1/2 in. for curved curbs.
(Editor’s Note: Since this article was first published, new materials have become available for projects like this. See Pro Tile Tips for more information.)
Anatomy of a Mortar Shower Floor
The first layer, called a sloped fill, is simply a mortar subfloor. It’s sloped toward a special two-piece clamping-type drain (available at any home center) that is made specifically for a mortar bed shower floor. The sloped fill slants from the drain toward the perimeter of the shower with a slope of 1/4 in. per foot. Since our shower had an average width of 3 ft., we sloped up from the 1/4-in. thickness of the drain to a 1-in. thickness around the shower walls and curb to get the necessary 3/4-in. slope.
The second layer, called the pan, is a durable CPE (chlorinated polyethylene) membrane. This vinyl liner is turned up at the edges to create a waterproof membrane in the shape of a shallow pan. Water that works its way through the grout and the top layer of mortar will flow down the slope to be drained through the weep holes of the drain. On top of the pan is a layer of expanded galvanized metal lath to reinforce the mortar. Over the lath a sloped mortar bed is laid using the same 1/4-in.-to-the-foot slope rule we used for the sloped fill.
Shower curbs help by containing water in areas that aren’t bordered by walls. If a drain becomes blocked, perhaps by a washcloth over the surface, a curb buys you time. It will dam the water within the shower for a while before it lets it run over onto the bathroom floor.
(For a larger version of this drawing, see Additional Information, below.)
Design and Layout
Photo 5: First layer of mortar
Remove the top half of the shower drain and plug the drainpipe with a rag to prevent debris from falling into the plumbing. Pack the mortar with a wood float, then screed the first layer of mortar. Use removable 1-in. screed blocks along curbs to establish a 1-in. to 1/4-in. slope toward the drain. Work the surface smooth with a wood float and smooth with a steel trowel. Let the mortar harden overnight.
Photo 6: Lay in the liner
Tack up scrap pieces of vinyl liner to protect the actual liner from the sharp edges of plumbing or electrical plates. Install the liner, running it up onto the walls at least 6 in., and nail it to the studs with roofing nails at the top edge. Feel the drain flange bolts with your fingers and draw and carefully cut the liner to fit just outside the bolts. Cut off the liner against the curved edge 1/2 in. below the top of the form.
Photo 7: Fold the corners
Chisel out the inside corners of the framing to create a recess for the liner folds.
Photo 8: Make a drain hole
Cut out the vinyl liner for the drain with a utility knife, cutting just outside of the bolt holes. Run a bead of silicone caulk around the outer edge of the flange, then bolt down the top half of the drain assembly. Cover the top of the drain with duct tape to protect it during installation of the mortar bed and tiling.
Photo 9: Attach the tile backer board
Install cement board over the vinyl liner and screw it to the studs with coated cement board screws every 8 in. Cut slots in the cement board to go over curbed areas against the walls. Tape the seams with fiberglass tape and thin-set mortar.
First, establish the shape and size of your shower. Our shower had several requirements. We wanted a shower that would comfortably accommodate two people and have two separately controlled shower heads. We also wanted a curved glass block wall on two sides and a drying area that was part of the same shower. The specifications for curving 8-in. glass block required a radius of no less than 65 in. After trying several arrangements on the floor using properly spaced glass blocks to help define the shape, we settled on a 24-in. (three glass blocks) straight run before beginning our curve. The size of the dry-off area was arbitrary. We just stood there and pretended to dry ourselves off and decided it was right.
Keep these elements in mind when you’re sizing and positioning your shower:
The tile layout. It’s easier to determine the size of the shower if your wall tile is selected ahead of time. Since we had 12-in. tile, we made small alterations in the size until we had wall lengths that made full tiles come out just behind the inside edge of the glass block.
Shower doors. If your shower will have a door, pick it out in advance to make sure the shower opening will accommodate it. Don’t forget to allow for the thickness of the tile and the cement board. When you’re determining the size of the shower door and the direction it should swing, consider other bathroom doors and fixtures.
Plumbing. It’s obviously much easier to hook up a new shower that is located near existing plumbing. Copper water lines, sewer drain lines and vents can be hooked up to pipes at a neighboring bathroom. Our shower backed up to a common wall that contained all the plumbing we needed. If you’re installing your shower in a remote location, it can be tough to get to the sewer drain and still keep the shower drain within the required distance from the drain water vent. You may need to rip out walls or the ceiling below the shower to accomplish hook-ups if the next level down is finished. Sometimes plumbing a new bathroom is more work than building the shower from scratch.
Now that the shower is laid out, it’s time to rip out the walls and rough in the plumbing. Cut the drywall out of the shower opening with a utility knife and remove it. We made our cutting line fall in the middle of the glass block. That way the seam between the drywall and cement board would be hidden behind the glass block, and we could easily slip backing boards behind the drywall to support the splice and to tie in the glass block later. After you plan your plumbing hook-ups, cut a hole for the clamping-type drain in the subfloor near the center of the shower so that the bottom flange of the drain rests on the subfloor. You may need to make small notches in the floor to allow for the plastic nubs that protrude from the sides of the bottom flange. Rough in the copper plumbing and drain water lines.
Form the outline of the shower floor with 2x4s in the straight areas. Toe-screw forms to the floor from the outside so you can easily remove them later. Hardboard siding ripped to 3-1/2 in. widths works great for handling curved curbs. The slope fill can be tricky to install because its 1-in. height is 2-1/2 in. below the top of the forms. For screeds, use permanent 1-in. strips around the walls and removable 1-in. strips to get the correct slope against the curbed edges (see Photos 4 and 5). After getting the sloped fill tamped into place, we lifted these blocks out and went back and filled in the voids. Don’t worry too much about the finish on the slope fill; just make sure it has the proper slope toward the drain. It just serves as a sloped base for the vinyl liner and as a base for the upper layers.
Install the cement board walls by setting them over the liner and on top of the sloped fill. Use hot-dipped roofing nails or the coated cement board screws that are available at the same place you buy your cement board. Tape the seams with fiberglass mesh tape and cover them with either thin-set mortar or mastic, whichever the tile store recommends for setting your tile. When setting the cement board, face the smooth side out. This makes it much easier to spread the tile adhesive and get a flat surface for tiling and for drawing tile layout lines.
Cut the lath with a pair of tin snips and lay it on top of the membrane. Be very careful cutting and fitting the lath. Avoid walking on the lath. Its sharp edges can puncture your waterproof membrane.
How to get curbs the proper width
Photo 10: Add the metal lath
Cut and lay in galvanized expanded metal lath on top of the liner just short of the cement board edges. Bend 12-in. x 3-ft. lengths of lath over a 2×4 for curb reinforcement pieces. Keep the height barely under the form heights. For a curved curb, make a series of slits every 10 in. to help it bend to the shape of the hardboard form.
Photo 11: Form the curb
Fold the vinyl liner and drop the pre-bent curb lath over the top of it. Poke a galvanized 10d nail through the lath and top edge of the liner to keep it from collapsing while you pack the curb with mortar.
Photo 12: Cover the lath with mortar
Snap chalk lines against the cement board, making them 1-1/4 in. above the sloped fill. Adjust the top of the drain by screwing it up or down until it is 1 in. above the top of the slope fill. Pile mortar against the wall and compact it down to the line. Use the packed mortar as a guide for screeding off the mortar between the wall and the drain.
Photo 13: Mortar the curb
Pack mortar into the lath with a wood float around the folded liner, then screed with a 3/4-in. plywood jig. After screeding, tool the edges of the curb with a trowel to obtain crisp edges.
Photo 14: Adjust the drain
Raise the shower drain by unscrewing it until it is the same height as the floor tile. You have to do this before the mortar sets.
The width of the curbs on our shower was determined by the width of the glass block. We used 4-in. thick blocks, which have a real width of 3-7/8 in. We wanted the finished curb, including the tile, to be slightly narrower than the block, so we subtracted the two layers of 3/8-in. tile (1/4-in. tile, 1/8-in. mastic) on each side of the curb from 3-7/8 in. and wound up with a curb 3-1/8 in. wide.
Since the top mortar bed is the tiling surface, make it as even as possible. Use the straightedge to locate high or low areas. Pack in mortar to fill depressions, and scrape off excess in the high spots. Use a steel trowel to smooth the bed and to tool sharp edges at all corners for a cleaner tiling job.
Required Tools for this Project
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
- Caulk gun
- Chalk line
- Cordless drill
- Framing square
- Needle-nose pliers
- Tin snips
- Utility knife
- Wood chisel
Required Materials for this Project
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.
- 1-1/4 in. roofing nails
- 10d galvanized nails
- 3-in. drywall screws
- Ceramic floor mix
- Duct tape
- Fiberglass mesh tape for cement board
- Galvanized expanded metal lath
- Hardboard siding
- Shower drain assembly
- Thin-set mortar
- Tile backer board
- Vinyl membrane