CSLB C-54 Tile Trade Exam Study Guide (2026)

Outline section 3, Installation and Repairs (33%): "Showers and steam rooms".^[1]

A shower is the hardest environment a tile contractor builds. The industry puts it in numbers: "A daily 15-minute shower represents 30 gallons of water per day or the equivalent of 3" of rainfall per day, which translates to 1100" of rainfall per year."^[2] A steam room adds heat and vapor pressure to that water. The exam tests two bodies of rules here: the plumbing and residential code requirements that a building inspector enforces (size, doors, liners, slope, tests, valves), and the tile-industry methods that make the assembly last (pre-slope, waterproofing, coverage, sloped horizontal surfaces, steam-room ceilings).

A caution about section numbers: California city handouts written to the 2025 codes cite the same shower requirements under different California Plumbing Code section numbers. This chapter teaches the requirement and names the code; learn the numbers, not the section labels.

7.1 Wet areas defined

The ANSI standard's introduction defines wet areas as "Tile surfaces that are either soaked, saturated, or subjected to moisture or liquids (usually water) such as in gang showers, tub enclosures, showers, floors adjacent to curbless showers, laundries, saunas, steam rooms, swimming pools, or exterior areas."^[3] Everything in this chapter is a wet area, so the 95 percent coverage minimum of Chapter 5 applies.^[4]

7.2 What the code requires of a shower

These are the requirements city building departments list for residential shower work under the 2025 California codes.^[5]

Size. "Shower compartments, regardless of shape, shall have a minimum finished interior of 1024 square inches and shall also be capable of encompassing a 30-inch circle." A receptor at least 30 by 60 inches is exempt.^[6] "The curb may encroach on these size requirements."^[7] The area and dimensions are maintained "to a point of not less than 70 inches above the shower drain inlet".^[8]

Door. "Any door shall have a clear opening not less than 22 inches".^[6]

Finish surfaces. Shower floors and walls "must be finished with a nonabsorbent surface. For walls, this must extend to a height at least 6 feet above the floor."^[6] Another handout puts it as waterproof "up to 72 inches above the drain inlet".^[7]

Liner. "Shower receptors must be constructed and lined with watertight materials". "Linings shall have no nails or perforations to a height at least 1 inch above the finished dam or threshold. Ensure that the subdrain weep holes are protected from clogging."^[6]

Test. "Shower receptors shall be tested for watertightness by filling with water to the level of the rough threshold. The test plug shall be so placed that both upper and under sides of the sub-pan shall be subjected to the test at the point where it is clamped to the drain."^[6] One department states the practice as "2-inches of water sitting for at least 24 hours".^[5]

Drain. "Showers require a minimum 2-inch drain and trap". When a tub is replaced with a shower, "the waste outlet and fixture tailpiece must be increased to at least 2″ in diameter if smaller than this".^{[6, 7]}

Valves and temperature. Valves must be "pressure balance, thermostatic, or combination pressure balance/thermostatic mixing valve type that provide scald and thermal shock protection", installed at the point of use.^[6] "The maximum water temperature to a shower or tub/shower combination is 120°F. The water heater thermostat cannot be used as the control for this temperature."^[7] Valves and showerhead are arranged so "the bather can adjust the valves before stepping into the shower spray".^[6]

Glass. "Safety glass (tempered or laminated) is required for all glass shower doors and partitions".^[7]

Backer. No water-resistant gypsum board behind tile in the shower; use cement board, fiber-cement or glass-mat gypsum (Chapter 4).^[5]

7.3 The traditional mortar-bed shower floor

This is the assembly the exam most often describes, from the subfloor up:

1. Pre-slope (sloped fill). "This slope, according to the TCNA Handbook is called “sloped fill” or commonly known as the pre-slope. This sloped material is installed under the pan liner". Every Handbook shower detail that uses a clamping ring drain "requires sloped fill (pre-slope) under the shower pan membrane."^[3] It exists so water that gets through the tile and mortar bed runs to the drain's weep holes instead of pooling on the liner.
2. Pan liner (the shower pan membrane) over the pre-slope, clamped at the drain, turned up the walls and over the curb, with no nails in the zone just above the threshold.^[6]
3. Flood test of the liner before anything covers it.^[6]
4. Wall backer lapped over the turned-up liner, fastened only in the top inch of the turn-up.^[9]
5. Mortar bed on the liner, of uniform thickness: "The mortar bed on top of the membrane is exactly the same thickness along the walls as it is at the drain. ANSI A108.01A section 2.3.6 requires that the mortar bed be 1-1/2” (38 mm)."^[3] The slope comes from the pre-slope beneath.
6. Tile, with 95 percent coverage and joints to the drain.

Slope. The finished floor slopes to the drain at a minimum of 1/4 inch per foot and, in the plumbing code as industry sources describe it, a maximum of 1/2 inch per foot.^{[3, 10]} The floor must also be flat: "there can be no low spots for birdbaths that could retain water."^[3]

7.4 Every horizontal surface slopes to the drain

ANSI A108.01 section 3.6.4: "All horizontal ledges/rims shall have a slope such that any fluid on their surfaces flows toward the drain." Every TCNA bathtub and stall-shower detail adds: "All horizontal surfaces, for example, shower seats, sills, curbs, etc., must slope towards a drain or other surface sloped toward the drain. Where present, waterproofing also must be sloped."^[3] That includes niche shelves, benches and windowsills.^[3] A curb about 5 inches wide "only needs to be sloped 1/8” from outside to inside" to meet the 1/4-inch-per-foot rule.^[3]

7.5 Surface-bonded (direct-bond) systems and curbless showers

Many showers now use a bonded waterproof membrane (A118.10) directly under the tile instead of a buried pan liner. The industry warns that these "direct bond shower systems typically don't have a weep system to evacuate moisture", so troweling voids under the tile become channels: "the ridges will not be flattened into the valleys, leaving aqueducts below the tile surface," and moisture wicks uphill into the tile or stone.^[2] Some membrane manufacturers state "that moisture-sensitive stone should not be used" with their systems.^[2] The fix is the Chapter 5 troweling method and the manufacturer's mortar.

For walls, the Handbook's receptor method requires "A waterproof membrane (A118.10) or vapor retarder membrane (A108.M-2.8.1) must be specified for walls".^[10]

Curbless showers. Without a curb, the bathroom floor near the shower becomes wet. One city's guideline for curbless residential showers: finished threshold height "a maximum of½ inch above the bathroom's finished floor level", with changes of level between 1/4 and 1/2 inch beveled no steeper than 1 in 2; the liner extending "a minimum 12 inches beyond the threshold and into the bathroom"; the drain inlet "a minimum of 2 inches below the top of the finished threshold"; a receptor able to hold "a minimum of 9.6 gallons above the top of the drain inlet"; and framing supporting "a live load of 40 psf and a minimum dead load of 20 psf".^[8] Another handout notes that without a threshold, "the rest of the room is to be considered a wet location."^[6]

7.6 Glass tile in showers

Large format glass (over 3 × 3 inches) in a shower brings thermal shock: "When cool glass is hit by hot water or steam ... the glass can expand rapidly and crack."^[11] The industry steps: get the glass manufacturer's written instructions and confirm the tile is rated for showers; flat substrate with minimal deflection; the manufacturer's glass-tile mortar; "An extended mortar cure time is required before grouting and applying the sealant to changes in plane"; and "All changes in plane must be filled with a 100% silicone sealant rated to adhere to glass."^[11]

7.7 Steam rooms

A steam room is a shower with vapor pressure and sustained heat, and the TCNA Handbook treats continuous-use steam showers in their own methods (SR613, SR614).^[12]

• Ceiling slope. The Handbook "requires that the ceiling of the steam shower be sloped at a rate of 2” per foot to eliminate condensed water droplets from falling on the user."^[3]
• Benches and horizontal surfaces slope 1/4 inch per 12 inches to the drain.^[12]
• Membranes rated for steam. "not all membranes are suitable for stream, high-temperature and/or chemical exposure, or exterior use." Check the manufacturer's rating.^[10]
• No organic adhesive where temperatures exceed 140°F.^[10]
• The rest of the envelope. "Insulation, air gaps, slip joints, and slope to drain are all critical elements that must be addressed and properly installed by the appropriate contractor."^[12]
• Tile-over caution. Cracked tiles in an existing steam room point to a failure somewhere in the system; verifying it may require removal (Chapter 3).^[12]

Worked example: a 36 × 48 inch shower with a bench

1. Size. 36 × 48 = 1,728 in², over 1,024, and a 30-inch circle fits.^[6]
2. Pre-slope. The drain is centered; the farthest corner is 30 inches away (2.5 ft). At 1/4 inch per foot the pre-slope rises 5/8 inch to that corner.^[3]
3. Liner and test. Liner clamped at the drain, weep holes protected, no fasteners in the low turn-up; flood-tested to the rough threshold.^[6]
4. Bench and curb. Both slope toward the drain; the 5-inch curb falls 1/8 inch inward.^[3]
5. Tile. 95 percent coverage; silicone, not grout, at the wall-to-floor and bench-to-wall changes of plane.^{[4, 11]}

A shower from rough-in to final: the inspection points

Think of a mortar-bed shower as a series of hold points, each of which must be right before the next layer hides it.

1. Framing. Curbless and sunken receptors need framing designed for the load and the slope; one city guideline asks for floor framing supporting a 40 psf live load and a 20 psf dead load.^[8]
2. Drain and pre-slope. Drain body set at the right height; sloped fill under the liner at 1/4 inch per foot, flat, with no birdbaths.^[3]
3. Liner. Watertight liner clamped at the drain, weep holes protected, no nails or perforations low on the turn-up.^[6]
4. Flood test. Filled to the rough threshold with the plug placed so both sides of the sub-pan are tested at the clamp; one department describes 2 inches held for 24 hours.^{[5, 6]}
5. Wall backer. A shower-rated backer lapped over the liner, fastened only in the top inch of the turn-up; no water-resistant gypsum board behind tile.^{[5, 9]}
6. Wall waterproofing or vapor retarder, as the Handbook's receptor method requires.^[10]
7. Mortar bed. Uniform 1-1/2 inches on the liner; screeded to the pre-slope's pitch.^[3]
8. Tile. 95 percent coverage; all horizontal surfaces sloped to the drain.^{[3, 4]}
9. Joints. Sealant, not grout, at changes of plane and at the receptor.^{[11, 13]}
10. Final. Valve type and location, 120°F maximum, safety glass, and a finish nonabsorbent to the required height.^{[6, 7]} One handout notes the inspector must be able to reach the shower valves from outside the enclosure at final.^[7]

Why showers fail, in one table

Failure	Cause	Chapter
Offensive odor from the shower floor	No pre-slope; water sits on the liner[3]	7
Leak into the room below at the curb	Liner nailed low or torn at the curb[6]	7
Dark grout lines that return after every use	Edge voids behind wall tile[4]	8
Stone darkening that climbs the wall	Uncollapsed ridges on a direct-bond system wicking water[2]	7
Water standing on a niche shelf or bench	Horizontal surface not sloped to the drain[3]	7
Dripping condensation in a steam room	Flat ceiling instead of 2 inches per foot[3]	7
Cracked glass tile	Thermal shock, rushed cure or no soft joints[11]	7, 9

Sources cited in this excerpt

1. License Examination Study Guide — Ceramic and Mosaic Tile (C-54), form 13E-54 (03-2026). Contractors State License Board (CSLB), 2026-03 (for examinations scheduled on or after July 1, 2023). https://www.cslb.ca.gov/Resources/StudyGuides/C54StudyGuide.pdf
2. How to Deal with Tile Discoloration in a Shower. Ceramic Tile Education Foundation (CTEF), accessed 2026-09-24. https://www.ceramictilefoundation.org/blog/how-to-deal-with-tile-discoloration-in-showers
3. Does Your Tile Slope To the Drain? Ceramic Tile Education Foundation (CTEF), accessed 2026-09-24. https://www.ceramictilefoundation.org/blog/everything-must-slope-to-the-drain
4. Never Assume You Have Sufficient Mortar Coverage. Check It. Ceramic Tile Education Foundation (CTEF), accessed 2026-09-24. https://www.ceramictilefoundation.org/blog/insufficient-mortar
5. Bathroom Requirements (2025 California codes; updated 01/2026). City of Rancho Palos Verdes, Building & Safety Division, updated 2026-01. https://www.rpvca.gov/DocumentCenter/View/19326/-Bathroom-Remodel-Requirements-PDF
6. Bathroom Remodel (Residential) submittal requirements. City of Milpitas, Office of Building Safety, accessed 2026-09-24. https://www.milpitas.gov/DocumentCenter/View/966/Bathroom-Remodel-Submittal-Requirements-PDF
7. 2025 California Codes — Bathroom Remodel Requirements (handout). City of San Bruno, Building Division, accessed 2026-09-24. https://www.sanbruno.ca.gov/DocumentCenter/View/9040/2025-Bathroom-Remodel-Handout
8. Curbless Shower Guidelines — Residential. City of Mill Valley, Building Department, accessed 2026-09-24. https://www.cityofmillvalley.gov/DocumentCenter/View/347/Curbless-Shower-Pans-PDF?bidId=
9. VA Master Specification Section 09 30 13 Ceramic/Porcelain Tiling. U.S. Department of Veterans Affairs, Office of Construction & Facilities Management (Technical Information Library), accessed 2026-09-24. https://www.cfm.va.gov/til/spec/093013.docx
10. What Do You Need to Install Tile in Wet Areas? Ceramic Tile Education Foundation (CTEF), accessed 2026-09-24. https://www.ceramictilefoundation.org/blog/installing-tile-in-wet-areas
11. Installing Large Format Glass Tile in a Shower: 10 Steps to Follow. Ceramic Tile Education Foundation (CTEF), accessed 2026-09-24. https://www.ceramictilefoundation.org/blog/installing-large-format-glass-tile-in-shower
12. Tile Over It or Take It Up? Ceramic Tile Education Foundation (CTEF), accessed 2026-09-24. https://www.ceramictilefoundation.org/blog/tile-over-or-take-it-up
13. Quick and Easy Movement Joints... the Right Way. Ceramic Tile Education Foundation (CTEF), accessed 2026-09-24. https://www.ceramictilefoundation.org/blog/quick-easy-movement-joints