A traditional mortar shower pan takes two days and a set of skills most tile setters spend years refining. A Schluter shower pan install compresses that into an afternoon, because the sloped foam tray arrives with the geometry already built in — 2 percent slope, dead flat planes, and a bore sized for the Kerdi drain. I have set both mud pans and Schluter trays for years, and the foam system is what I now put in my own rentals when speed and a warrantied assembly matter.
Part of our Bathroom Remodeling & Flooring guide — explore the full guide →
Speed does not mean foolproof. Every failed Schluter shower pan install I have been called to autopsy died at the same three points: a starved thinset bed under the tray, unmodified-versus-modified thinset confusion, or seams banded with dry spots. This guide walks the full sequence — substrate, drain, tray, membrane, seams, and flood test — with the details that keep you off that autopsy list.
What Comes in the System
The Kerdi-Shower-Kit bundles most of what the pan needs. Typical contents and street prices:
- Kerdi-Shower-ST tray: expanded polystyrene, center drain, common sizes 32×60, 38×38, 48×48, and 72×72 inches; trays alone run $180-$420. Off-center LTS versions serve linear layouts.
- Kerdi-Drain: 4-inch square stainless grate with a bonded PVC or ABS flange — order the flange to match your waste pipe plastic; mixing PVC cement on ABS pipe is a leak and a code violation.
- Kerdi membrane: 8-mil orange polyethylene sheet, sold in the kit or by the foot off a 39-inch-wide roll.
- Kerdi-Band: 5-inch seam tape; Kerdi-Kereck preformed inside/outside corners.
- Curb: a foam Kerdi-Shower-SC curb, typically 4-1/2 inches tall.
Complete 32×60 kits land around $500-$700. Add thinset, a 1/4 x 3/16 inch V-notch trowel, and a 6-inch drywall knife for embedding band.
Substrate Prep Before Anything Orange Appears
The tray wants a flat, structurally sound floor: plywood or OSB subfloor in wood framing, or clean concrete on slab. Flat means within 1/4 inch over 10 feet — shim or grind humps, because foam follows whatever it sits on. Walls should already carry your tile backer (Kerdi-Board, cement board, or even standard drywall, which Schluter explicitly permits under full Kerdi coverage) run to within about 1/4 inch of the tray’s future surface.
Rough in the drain so the 2-inch riser is cut to accept the Kerdi-Drain flange at exactly tray height. Dry-fit ruthlessly here: set the tray, drop the drain in the bore, and confirm the flange top sits flush with the tray’s top surface. Trim the riser in 1/8-inch bites — you can always cut more, and a proud drain telegraphs through the tile forever.
Setting the Drain and Tray
Work in this order once the dry-fit checks out:
- Solvent-weld the drain flange to the riser using the correct primer and cement for your pipe material. Let it set 15 minutes.
- Mix unmodified thinset (Schluter Set or an ANSI A118.1 mortar) to a creamy peanut-butter consistency.
- Trowel a full bed over the entire footprint with the 1/4 x 3/16 V-notch, combing one direction. No bare islands — voids under foam become crunchy dead spots and cracked grout.
- Lower the tray into place, aligning the bore over the flange, and walk it in with flat-footed body weight from center outward. A slight ooze at the edges tells you the bed is full.
- Check every plane with a 4-foot level: the perimeter should read level, the slope planes consistent. You have maybe 10 minutes of adjustment time.
Set the foam curb the same way at the entry — thinset to the floor and to the tray edge — unless you are framing a curbless entry, which requires recessing the subfloor and is its own planning exercise.
Membrane: Covering the Field
Cut Kerdi to run up the walls a minimum of 3 inches above the tray, and panel the walls from the top down so lower pieces lap under upper ones shingle-style. For each sheet: trowel unmodified thinset onto the substrate with the V-notch, embed the membrane, then squeegee it flat with the drywall knife pulling from center to edges. You are chasing full contact and zero air pockets — a proper embed shows thinset color faintly shadowing through the orange.
Timing note that trips people up: you can tile as soon as the membrane is embedded, but do the flood test at 24 hours minimum so the thinset under seams has cured enough to resist water pressure. Cold rooms below 60 degrees F stretch every cure time; give it an extra half day in a winter basement.
Seams, Corners, and the Drain Collar
Every joint gets 2 inches of minimum overlap, and this is where discipline pays:
- Tray-to-wall junction: Kerdi-Band folded lengthwise into the corner, embedded in thinset on both faces, squeegeed until excess creams out along the edges.
- Inside corners: preformed Kereck corners first, then band laps over their legs. Hand-folded corners work but take origami practice; the $6 preforms are cheap insurance.
- Curb: wrap with band or a membrane piece over the top and down both faces, lapping onto the field membrane 2 inches.
- Drain: the kit’s pre-cut Kerdi collar embeds over the flange’s fleece ring. Comb thinset on the flange, seat the collar, and squeegee outward from the bore. Then install the grate assembly, which threads to height later to match tile thickness.
Run your fingertips along every banded edge after embedding. Any spot that feels hollow or papery gets re-troweled now, not discovered during the flood test.
The Flood Test
Plug the drain with an inflatable test ball or a Schluter test plug, fill the pan with about 1 inch of water — mark the level with tape — and leave it 24 hours where your inspector does not specify otherwise. Zero drop, aside from a hair of evaporation, is the passing grade. If the level falls, check the drain collar first; 8 of 10 leaks live there, usually a dry spot where thinset was combed too thin over the flange.
Photograph the filled pan with a timestamp before draining. Inspectors love it, and if a dispute ever arises about workmanship, that photo is your best friend.
Tiling Over the Finished Pan
Tile choice on a Kerdi tray is a geometry decision before a style decision. The factory slope planes converge at the drain from four directions on a center-drain tray, which means large-format tile cannot lie flat across those transitions — 2-inch mosaics remain the standard answer because each small tile articulates over the slope changes, and their extra grout lines double as slip resistance. If the design demands bigger floor tile, that is the argument for the off-center LTS tray or a linear-drain layout, where a single slope plane will carry tile up to 12 by 24 without lippage games.
Set floor tile in the same unmodified or All-Set mortar, back-buttering mosaics so coverage hits 95 percent in a wet zone. Thread the Kerdi grate assembly to final height before the floor goes down — the grate should land flush with the finished tile plane, and dialing it after the mortar cures means fighting cured thinset in the threads. Finish the perimeter and all plane changes with a color-matched 100 percent silicone joint rather than grout; movement joints at changes of plane are a TCNA requirement and the difference between a hairline-free pan and a callback.
Mistakes That Sink This System
- Modified thinset between membrane and tile in sealed sandwiches: Schluter specifies unmodified mortar against Kerdi because modified needs air to cure. Their warranty position has softened with Schluter All-Set, which is approved for both — when in doubt, use All-Set everywhere and stop thinking about it.
- Thinset too dry: band will not wet out and leaves capillary channels. Err creamy.
- Cutting the tray to fit an alcove without re-establishing the perimeter: trays trim fine with a hand saw, but keep cuts to the outer edges so the slope geometry survives.
- Screwing anything through the pan afterward: grab bars and glass panels get blocking planned before membrane, or surface-anchored solutions after.
- Skipping the flood test to save a day: the one step that proves all the others.
Done in the right order, a first-timer gets a warrantied, waterproof pan in a single focused day plus a test day — and a tile-ready surface flatter than most 20-year mud men can float. That trade is why the orange membrane took over the industry.
