When homeowners look at a finished tile shower, they see the tile, the grout lines and the glass. What they don't see is the layer that does the real work: the waterproofing membrane. Tile and grout are not waterproof. Grout is porous, and water soaks through it every single time you shower. The membrane behind the tile is what keeps that water out of your walls, framing and subfloor.
Most leaking showers I tear out in the Phoenix area didn't fail because of bad tile. They failed because the waterproofing behind the tile was missing, incomplete, or skipped at the corners. So instead of telling you we waterproof properly, here's a photo from a real project, taken right before tile installation.
What You're Looking At in This Photo
Everything you see in pink and purple is waterproofed with RedGard, a liquid-applied waterproofing membrane. It's rolled and brushed on in coats until it forms one continuous rubber-like layer. RedGard goes on pink and turns red as it dries, so the color shows us exactly where the coverage is complete and fully cured. No thin spots or missed areas end up hiding behind the tile.
Here are the five areas in this shower where most leaks start, and how each one was handled:
1. The walls, floor to ceiling of the wet area
Every wall that will get wet is fully coated, not just the area directly under the showerhead. Water splashes, runs and wicks. If the membrane stops short, the water finds the edge.
2. The inside corners and the wall-to-floor joint
Corners are where walls move slightly against each other, and where cheap installs fail first. Look at the bottom edge of the walls and the inside corner in the photo: the membrane is heavier there, and it runs continuously from the walls down to the floor, so there's no seam for water to slip through.
3. The recessed niche
A shampoo niche is a box cut into your wall, which means four inside corners, a bottom ledge that holds water, and a back that sits right against the wall cavity. In this shower, the entire niche is coated, including the back, the sides and the bottom ledge. A niche that's only "mostly" waterproofed is one of the most common leak sources we find during tear-outs.
4. The window in the shower
A window inside a shower is common in older Phoenix homes, and it's one of the riskiest spots in any bathroom. Water sits on the sill, runs down the frame, and finds any gap. Here, the membrane wraps the window opening, including the sill and the side returns. When the tile goes on, the sill gets pitched so water drains back into the shower instead of pooling against the window.
5. The valve, the curb and the drain
The shower valve and the supply opening are holes in the waterproofing by design, so they get sealed around the opening before the trim goes on. The curb, the low wall you step over, is wrapped on the top and both faces, because it takes direct water every day. The floor is a sloped mortar bed pitched toward the drain, which is taped off in blue so nothing falls in while we work.
The floor has its own waterproof layer you can't see in the photo: a shower pan liner installed under the mortar bed. Any water that makes it through the grout and mortar is caught by the liner and carried to the drain, instead of soaking into the slab or subfloor. This is the traditional, proven way to build a custom tile shower floor, and it lets us build any size or shape of shower, not just the sizes a prefab pan comes in.
Why this matters in Phoenix: Our hard water and big temperature swings are tough on grout and caulk. Grout will need maintenance over the years no matter what. With a proper membrane behind it, worn grout is a cleaning chore. Without one, worn grout is a leak.
Liquid Membrane vs. Sheet Membrane (Schluter KERDI)
There are two main ways to waterproof a tile shower, and both work when they're installed correctly. We choose based on the shower's layout.
| Liquid-applied membrane (e.g. RedGard) | Sheet membrane (e.g. Schluter KERDI) | |
|---|---|---|
| How it goes on | Rolled and brushed on in multiple coats | Fabric sheet bonded to the wall with thinset, seams overlapped |
| Best for | Niches, windows, benches, odd angles and lots of penetrations | Large flat walls and standard layouts |
| Thickness | Depends on correct coats; color helps confirm coverage | Fixed thickness from the factory |
| What makes it fail | Too few coats, thin spots, rushing the cure time | Unsealed seams, poor thinset coverage at the corners |
The product matters less than the details. Either system fails if the corners, niche, window, valve or curb are skipped. That's why, whoever builds your shower, you should ask to see the waterproofing before tile goes on.
What a Shower Without Waterproofing Looks Like Later
If your shower is 15 to 20 years old or more and was never redone, there's a fair chance it was built on drywall, greenboard or a plastic sheet instead of a real membrane. These are the signs the water is already getting through:
- Hollow-sounding tiles when you tap them with a knuckle
- Mold that comes back within days of cleaning
- Grout that crumbles or keeps cracking in the same spots
- Stains, bubbling paint or soft drywall on the wall outside the shower, or on the ceiling below
- A musty smell that doesn't go away
At that point, regrouting or recaulking only covers the symptom. The fix is a tear-out down to the studs and a new, properly waterproofed shower. We go through this in more detail in 5 Signs Your Shower Tile Needs Replacement.
5 Questions to Ask Any Contractor About Waterproofing
Whoever you hire for your shower, ask these before you sign. A good installer answers them without hesitating.
- What waterproofing system will you use? You want a named membrane, not "we use green board" or "the grout is sealed."
- How do you handle the niche, window and bench? These need their own detailing, not just a pass with the roller.
- Is the membrane continuous from the walls to the floor and over the curb?
- Will you send me photos of the waterproofing before tile goes on? Once tile is up, you'll never be able to check. (We send ours to any customer who asks.)
- Are you licensed with the Arizona ROC? You can look up any contractor's license on the Arizona Registrar of Contractors website. Ours is ROC #311992.
Why We Don't Use Acrylic Liners or Glue-Up Panels
Acrylic liners and glue-up wall panels go in fast because they cover the old shower instead of fixing what's behind it. If the original shower was leaking, the new liner sits right on top of the problem. A real tile shower starts from a clean tear-out and a waterproofed substrate, which is why it lasts decades instead of years. You can read more on our tile vs. acrylic comparison.
Frequently Asked Questions
Does a tile shower need waterproofing?
Yes. Tile and grout are not waterproof. The membrane behind the tile is what keeps water out of your walls, framing and subfloor.
Is a window inside a shower a problem?
It can be done right, but it's a common leak point. The waterproofing has to wrap the sill and side returns, and the sill should slope back into the shower.
How is a custom tile shower floor waterproofed?
We install a waterproof shower pan liner under a sloped mortar bed. Any water that gets through the grout is carried to the drain instead of into the slab or subfloor.
Can you tile over my old shower to save money?
We don't recommend it for showers. Tiling over old tile hides what's behind it and makes a continuous membrane impossible.
How can I tell if my shower was waterproofed?
Once the tile is on, you usually can't. Watch for hollow tiles, returning mold, crumbling grout and stains near the shower. For a new shower, ask for photos before tile goes on.
