Things You'll Need
Exterior grade 19/32-inch plywood
Concrete backer board
Liquid waterproof membrane
Prespaced 2" tiles on mesh
Cove base tiles
Drain and faucet assembly
1/4" square toothed trowel
Rubber grout float
Use a utility knife to cut the glass fiber mesh on cement backer board, and then snap it against a straight edge. Cut the mesh on the back side after snapping the board.
Pay particular attention to getting the first layer of mortar properly sloped, as this determines the drainage of the tub.
Tack a 1/2-inch wood strip at the top of the tub sides as a guide for the depth of the mortar. Remove this guide after smoothing the mortar along the sides.
Use kitchen and bath caulking to seal the joints where the tile meets the wall.
Make sure the floor is strong enough to hold the weight of both the tub and the water it will hold.
Use proper safety procedures when handling all materials.
Be careful not to puncture the waterproof membrane when installing mortar over it.
Building your own bathtub is not an inexpensive or easy process, but it can be done. Tubs can be built from wood, concrete or tile-covered masonry. Probably the easiest is to build a tub with concrete backer board and tile it. A homemade tub will generally cost more than a purchased tub, but can be shaped to fit an unusual space or made longer, taller or wider than standard tubs.
Lay out the size and shape of the tub and build a frame of 2-by-4s. Join the lumber using butt joints and at least 3 screws per joint. The minimum spacing of the framing lumber should be 16 inches. Install side walls at right angles to the floor, but angle the back of the tub so that is comfortable to lean against.
Rough-in the plumbing for the drain and faucet. Install two layers of 19/32-inch exterior grade waterproof plywood on the floor of the tub to provide adequate support. Offset joints at least 6 inches.
Cut a 4.5-inch hole in the plywood where the drain will go. Disassemble the drain and lay the drain base in the hole so the flange of the drain base rests on the plywood. Solvent weld the drain base to the drain pipe. Cover the drain base opening with duct tape to keep materials from falling into the drain.
Fasten concrete backer board to the frame using screws designed for concrete backer board. Space the screws every 6 inches. Cut and fit the backer board as tightly as possible to make it easier to seal the tub. Cover the joints with adhesive and immediately embed backer tape.
Apply Portland cement/sand mortar mix over the floor of the tub so that it slopes toward the drain at 1/4 inch per foot. The mortar bed should be flush with the top surface of the drain base.
Trowel a thick, smooth layer of waterproofing over the entire tub to a minimum of 2 inches above the overflow drain. Allow that to dry, and then add another coat. When the second coat is dry, place the clamping ring for the drain over the bolts and slide the ring counterclockwise until it is tight. Plug the drain; fill the tub with water and let it sit for at least four hours. Drain the tub and repair any leaks before proceeding.
Place pea gravel over the weep holes in the drain assembly so mortar does not completely block them. Determine the finished height of the floor of the tub and screw the drain barrel and strainer into the clamping ring so that the drain barrel will be flush with the bottom of the tub.
Lay a 1 1/2-inch bed of mortar on the tub floor. When it is dry attach expanded metal mesh 2 inches above the water line and cover the sides of the tub with 1/2 inch of mortar. Allow the mortar to cure before installing tile.
Install tile using thin-set mortar. Lay tile on the tub floor first, cutting tile to fit around the drain and to accommodate the slope. Install the cove tile in the corners where the floor meets the wall. Use a straight edge to start and a level to ensure you keep the tile level as it rises up the sides of the tub. When the mortar cures, fill between the tile with grout. Mix 75 percent sanded grout and 25 percent nonsanded grout.
Install the overflow drain and faucet.
Lynn Doxon has a Ph.D. in horticulture, is a retired cooperative extension specialist and teaches courses in urban farming. She is the author of three books: "The Alcohol Fuel Handbook," "High Desert Yards and Gardens" and "Rainbows from Heaven." Doxon wrote the Yard and Garden column for the "Albuquerque Journal" and numerous magazine and newspaper articles and cooperative extension service guides.