How to Build Concrete Shower Pans on Slab Floors
Home remodelers sometimes want install a new shower on an existing concrete floor, such as in a basement. Rather than installing a prefabricated shower unit, reinforced plastic or fiberglass pan, they may prefer to build a custom concrete shower pan. Builders prefer mortar to actual concrete. Some local building codes allow concrete shower pans poured directly onto concrete floors without an underfloor liner membrane. However, current plumbing provisions of the International Residential Code (IRC) recommend shower liners. Does this Spark an idea?
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Things You'll Need
- Wood studs
- Carpenter nails
- Shower drain assembly
- Painter tape
- Concrete masonry block
- Thinset mortar mix
- Dry pack mortar mix
- Water
- Hand trowels
- Silicone sealant
- Cement backer board
- Crushed pebbles
- Corrosion-resistant wire mesh
- Level
Instructions
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Installation
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1
Locate shower drain rough-in. Ensure concrete floor is clean, dry and level. Install shower wall framing. Ensure dimensions comply with local codes. Install shower clamping drain assembly base, flange flush with subfloor. Cover drain opening with painter's tape to prevent clogging from debris.
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2
Install a single course of concrete masonry blocks, spanning the width of the door opening, between wall studs to serve as the foundation for the shower curb. The top of the curb should be 2 inches to 9 inches above top of shower drain.
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3
Prepare dry pack mortar mix. Following manufacturer's instruction, add water to mix with hand trowel until clumpy but not runny. The mixture should retain its shape when squeezed by hand, with no water draining. Prepare thinset mortar-based adhesive mix. Consult a local tile store for recommended mix, and mix according to the manufacturer's directions. Apply a thinset layer over the concrete floor.
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4
Deposit clumps of mortar at even intervals over the thinset. Using a hand float trowel, spread and compact the mortar across the shower floor, sloping from walls to drain. The slope should be from ¼ -inch minimum to ½-inch maximum per linear foot. Verify the surface slope using a level. Ensure the same height at corners of shower and 1-inch minimum mortar thickness at the drain. Keep top of mortar flush with top of drain. Let the mortar dry for 24 hours. Remove the tape from the drain. Apply silicone sealant around the drain base. Insert the ring bolts loosely onto base.
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5
Attach the cement backer board to the framing above the membrane. Notch studs 1/8-inch deep to height of the shower membrane to accommodate the liner. Install the shower membrane over the floor. Smooth excess material against wall framing. Fold using hospital-corner technique at corners. Nail the membrane to the notched studs, under the backer board, ½-inch from the top edge of the membrane. Press the membrane against the inside edge of the curb, over the top, and cover the face of curb. Trim excess.
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6
Cut openings in liner for the drain and bolt head penetrations. Attach the locking ring over the drain bolts then base and secure. Cover the drain with painter's tape. Leave 1.5 inches to accommodate the thickness of the second mortar bed, adhesive and tile. Fill liner with 1 inch of water. After 24 hours, measure depth at curb. Locate any leaks and seal. Remove tape, clear weep holes, and attach the drain top. Add crushed pebbles around the drain weep holes.
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7
Mix mortar as before, and install half of the mixture over the membrane. Lay the corrosion-resistant wire mesh. Cover the mesh with the rest of the mix. Apply a layer of mortar over the three exposed sides of curb. Screed, tamp and level the mortar with screed and float trowel. Ensure a positive drainage slope as before.
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1
Tips & Warnings
If a drain rough-in is not provided, hire a licensed professional plumber to connect the shower drain to the main building drain.
If the concrete floor is not level, use self-leveling compound to fill any voids and smooth any bumps, as needed.
If making dry pack mortar from scratch, combine one part portland cement to five parts dry sand. Mix together with trowel wearing protective gloves.
Always check local building code requirements for minimum shower dimensions, threshold heights, shower pan liner membrane recommendations, and other material and methods criteria.
References
- The Homebuilding Process; Rich Binsacca; 1999
- Code Link; State of Oregon Building Codes Division; January/February 2002
- International Building Code 2009; International Building Code Council; 2009
- North American Tile: Shower Floor
- Home Additions Plus: How to Mix Thinset Mortar: Mark Donovan
- John Bridge: How to Build Shower Curbs (Shower Dams)
Resources
- Photo Credit Jupiterimages/Photos.com/Getty Images
