Short definition
A shower base (also called a shower pan, receptor, or tray) is the bottom of a stand-up shower stall — collects water and channels it to the drain. Three construction types: pre-formed (drop-in acrylic, fiberglass, or cultured stone), custom mortar pan (built up on site), and modern foam pre-slope (Schluter Kerdi-Shower, Wedi). UPC requires 1/4 inch per foot slope toward the drain.
What it is
The three construction types:
- Pre-formed. A single-mold receptor in acrylic, fiberglass, or cultured stone. Drops into the framed opening; you plumb the drain from below; finished bottom and sides come from the factory. Sizes: 30×30, 30×36, 36×36, 32×60, 36×60, 42×60 inches are common.
- Custom mortar pan. Built up on site: a sloped mortar bed, a CPE or PVC sheet liner, a second mortar bed on top, then tile. Maximum aesthetic flexibility; demands skilled tile work; takes the most time.
- Foam pre-sloped (Schluter-Kerdi-Shower, Wedi). Foam slope panels with bonded waterproof membrane; preferred for tile-finished curbless and wet-room installs. Faster than mortar; more reliable than mortar on the waterproofing front.
UPC 411 requires 1/4 inch per foot slope toward the drain — this is true of all three types and is the single most important number in any shower-base install.
Why it matters to a homeowner
The shower-base decision drives the rest of the shower budget.
- Pre-formed acrylic base ($200 to $700). Easiest DIY; quickest install; aesthetic limited to what’s molded. Matches an alcove tub-shower kit naturally.
- Mortar pan ($500 to $2,000 in labor and materials). Custom tile finish; requires a skilled tile setter; pan leak test is non-negotiable before tiling.
- Foam pre-sloped kit ($300 to $900 for the kit). Modern preferred for tiled showers; bonded membrane simplifies waterproofing; works for curbless installs.
The most expensive shower repair in residential plumbing is a leaking custom mortar pan discovered after years of slow saturation: the tile, mortar bed, liner, and sometimes subfloor and joists below all need to come out. $5,000 to $15,000 is typical. The way to prevent it: a pre-tile leak test (24-hour flood test with the drain plugged) before any tile goes down. See shower-pan leak test.
If you’re inheriting an older shower with a leaking pan, a band-aid repair from the surface rarely holds — full pan replacement is the right answer.
Common failure modes
- Mortar pan liner punctured. Slow leak under tile; expensive remediation.
- Pre-formed base flexes from inadequate support. Caulk seams crack; water seeps. Mortar bed under the pre-formed base prevents flex.
- Inadequate slope. Water pools.
- Drain not low enough below floor. Water sits above drain rim.
Common variants
- Pre-formed (drop-in) vs. mortar pan (built up) vs. foam pre-slope (Kerdi). Construction type axis.
- Curbed shower base vs. curbless shower base. Different drain options; foam systems handle both.