How to Build an ADU, Day 13: Bathroom Tile & Shower

Jaime Costilla · 2025-03-13

Creating a Beautiful, Watertight Bathroom

The bathroom is often the most complex room in an ADU, square foot for square foot. Between waterproofing, plumbing, tile, and fixtures, there's a lot happening in a small space. The tile work, in particular, is where craftsmanship really shows — and where cutting corners leads to expensive failures.

Waterproofing: The Foundation of Every Good Shower

Before a single tile is set, the shower and tub areas must be waterproofed. This is non-negotiable and, when done wrong, is the #1 cause of bathroom failures.

Waterproofing Methods:

Kerdi Membrane System (Our Preferred)

Schluter Kerdi is a thin, flexible waterproof sheet bonded directly to the substrate
Creates a fully waterproof barrier behind the tile
Integrated with Kerdi-Band at corners, seams, and pipe penetrations
Also acts as a vapor barrier, preventing moisture migration into the wall cavity

Liquid-Applied Membrane

Products like RedGard or Hydroban are brushed or rolled onto cement board
Two coats, with reinforcing fabric at corners and changes in plane
More affordable but requires careful application for full coverage

Traditional Hot Mop

Hot asphalt is mopped onto the shower pan
Old-school method, still used on some shower floors
Very reliable when done by experienced crews

Shower System Components

Shower Pan The base of the shower, sloped to direct water to the drain. Options include:

Mortar bed (mud pan): Custom-built on-site, sloped to drain — traditional and reliable
Pre-formed pan: Factory-made foam or fiberglass base — faster installation
Linear drain system: Modern look with a slot drain at one edge — requires precise slope

Cement Board Substrate Tile needs a stable, moisture-resistant substrate. We use cement board (Durock, Hardie, or Kerdi-Board) on all shower walls — never standard drywall, which will fail when exposed to moisture.

Niches and Shelves Built-in shower niches (for shampoo, soap, etc.) are framed during the rough-in phase and tiled to match. They're a small detail that makes a huge difference in daily use.

Tile Selection for ADU Bathrooms

Floor Tile

Porcelain or ceramic with a textured/matte finish for slip resistance
Smaller formats (2x2 mosaic, 4x4, or hexagon) are best for shower floors — they conform to the slope better
Larger format tiles (12x24) work great on bathroom floors outside the shower

Wall Tile

Subway tile (3x6 or 4x12) is the most popular and timeless choice
Large-format porcelain (12x24 or 24x48) creates a modern, seamless look
Accent tiles or decorative patterns in niches add visual interest
Full-height tile (floor to ceiling) is a premium touch that makes the room feel larger

Popular ADU Bathroom Tile Styles:

Classic White Subway: Clean, timeless, brightens small spaces
Marble-Look Porcelain: Luxury look without marble maintenance
Matte Black & White: Bold, modern contrast
Wood-Look Porcelain: Warm, natural feel (great on floors)
Zellige or Handmade: Artisan character with slight variations

The Tile Installation Process

Step 1: Substrate Prep (1 day) Cement board is installed, seams are taped, and waterproofing is applied. Everything must be level and plumb — tile magnifies any imperfection in the substrate.

Step 2: Layout & Planning (half day) Before setting tile, the installer does a dry layout to determine:

Where cuts will fall (avoiding thin slivers at edges)
How patterns align at corners and transitions
Where accent tiles or borders will be placed
Niche tile alignment with surrounding walls

Step 3: Tile Setting (2-3 days)

Thinset morite is applied to the substrate with a notched trowel
Tiles are pressed into the thinset and leveled with spacers and a leveling system
Working from the bottom up on walls, ensuring each row is level
Cuts are made with a wet saw for clean, precise edges

Step 4: Grouting (1 day)

After thinset cures (24 hours), grout is packed into the joints
Excess grout is wiped clean with a damp sponge
Grout color choice matters — lighter grout shows more dirt, darker grout hides it but can look heavy

Step 5: Sealing and Caulking (half day)

Grout is sealed to prevent staining and moisture penetration
Silicone caulk is applied at all changes in plane (where walls meet floors, where walls meet other walls) — these joints move slightly and need flexible caulk, not rigid grout
Around fixtures (faucet escutcheons, shower valve trim)

Common Bathroom Tile Mistakes to Avoid

Using drywall instead of cement board in wet areas — guaranteed mold and failure
Skipping waterproofing — even with cement board, you need a waterproof membrane
Using floor tile on shower walls — some floor tiles are too heavy for walls
Grout in movement joints — where surfaces meet at angles, use silicone caulk, not grout
Thin slivers of tile at edges — poor layout planning creates ugly, fragile cut pieces
Rushing the cure time — thinset and grout need full cure time before getting wet (typically 24-48 hours)

Budget

Tile material: Costs vary by material — porcelain, natural stone, and specialty options available
Installation labor: $8–$18 per square foot
Waterproofing: $1,500–$3,500
Total bathroom tile budget: $4,000–$12,000 depending on size and material choices

Pro Tips

Spend more on shower tile, save on floor tile — you see the shower every day, and that's where quality matters most
Use larger grout joints (1/8" to 3/16") for easier maintenance and more forgiving installation
Pick grout color carefully — test it on a sample before committing
Plan your niche location around your tile layout so you get full tiles framing the opening
Consider a curbless (barrier-free) shower — it's accessible, modern, and makes a small bathroom feel bigger

Coming Up Next

Day 14: Flooring — choosing and installing the right flooring throughout your ADU, from LVP to tile to hardwood.

Vision ADU's tile setters deliver beautiful, long-lasting bathroom installations. Get your free estimate today.