Every shower remodel begins with a critical decision most homeowners never think about: what happens behind the tile? The waterproofing layer is the invisible foundation that decides whether water stays inside the shower or works its way into your walls and subfloor. At Showerly, every tile shower we build goes over a bonded waterproofing membrane that meets ANSI A118.10, because water damage from cut corners is one of the most expensive shower failures to fix.
What Is ANSI A118.10 and How Does It Work?
ANSI A118.10 is the American National Standard for load-bearing, bonded waterproof membranes installed under tile. The sheet membranes we use are pliable, with a soft polyethylene core and anchoring fleece laminated to both sides. When installed over cement board or drywall, the fleece bonds directly to thin-set mortar, creating a continuous waterproof barrier across your entire shower enclosure.
Unlike liquid-applied membranes, which depend on the installer reaching a consistent thickness, a sheet membrane has the same factory-made thickness everywhere. The membrane is only 8 mils thick (about the width of two sheets of paper), yet it forms a continuous barrier against water. The fleece layers on each side serve a dual purpose: the back side bonds to the substrate with thin-set, while the front side provides a mechanical bond for the tile thin-set.
Vapor Management: The Hidden Problem Solvers
One of ANSI A118.10's most misunderstood benefits is vapor management. In a hot shower, steam doesn't just rise — it drives moisture vapor through grout lines and into wall cavities. Traditional cement board installations without proper waterproofing allow this vapor to condense inside your walls, creating a perfect environment for mold growth you'll never see until major damage occurs.
ANSI A118.10 acts as both a waterproofing and vapor-retarding layer. It stops liquid water and significantly reduces vapor transmission, helping keep your wall cavities dry. This is particularly important in North Carolina's humid climate, where indoor humidity levels can compound the moisture load from daily shower use.
ANSI A118.10 vs. Other Waterproofing Systems
Homeowners researching waterproofing often encounter several competing products. Here's how they compare:
RedGard (Custom Building Products)
RedGard is a liquid-applied waterproofing membrane that you roll or brush onto cement board. While it's popular among DIYers and budget-conscious contractors, it has significant limitations:
- Application consistency: RedGard must be applied at a minimum thickness of 30 mils (dry). If the applicator rushes or misses spots, those thin areas become failure points. There's no practical way for a homeowner to verify coverage after installation.
- Cure time dependency: RedGard requires a full cure (typically 24-72 hours depending on humidity) before tiling can begin. In humid Raleigh conditions, cure times can extend further.
- Crack bridging: RedGard can bridge hairline cracks, but its performance degrades over time with substrate movement.
Laticrete Hydro Ban
Laticrete Hydro Ban is another liquid-applied option with better performance characteristics than RedGard. It offers faster cure times and slightly better crack-bridging capability. However, it shares the same fundamental limitation: consistent application thickness relies entirely on installer skill and attention.
Traditional Felt Paper and Mud Beds
The old-school approach — hot-mopping felt paper over a mud bed (mortar bed) — was the standard for decades. While a properly installed mud bed can last, the process is labor-intensive, adds significant weight to walls, and leaves more room for installer error. Most importantly, it requires highly specialized skill that fewer contractors possess today.
Why We Use Sheet Membranes
A sheet membrane takes most of the application guesswork out: the thickness comes from the factory, not from how evenly someone rolled it on. Sheet systems also include factory-made corners, pipe seals and mixing valve seals, so the most vulnerable points in your shower are protected with engineered pieces — not improvised caulk or liquid membrane patches.
How We Install ANSI A118.10 at Showerly
Our membrane installation follows the manufacturer's installation instructions, and the waterproofing is photographed before any tile goes up:
Step 1: Substrate Preparation
We install cement board (HardieBacker or equivalent) over wall studs, ensuring all seams are tight and surfaces are clean. Every screw is set flush, and we verify the substrate is flat within 1/8" over 10 feet.
Step 2: Pre-Formed Corner and Seal Installation
Before applying the main membrane sheets, we install pre-formed corners at every inside and outside corner, and pipe penetrations get factory-made pipe and mixing valve seals. These pieces protect the points where shower waterproofing most often fails.
Step 3: Sheet Membrane Application
We apply modified thin-set mortar to the substrate, then press bonded waterproof membrane sheets into the mortar. Each sheet overlaps the adjacent sheet by a minimum of 2 inches, and the overlap is also fully bedded in thin-set. We work from the bottom up, pressing out gaps and air pockets as we go.
Step 4: Photos Before Tile
Before a single tile goes up, we photograph the complete waterproofing installation and look it over. In our project system, the waterproofing/prep stage cannot be marked complete until at least one photo of it is in your Proof Pack — see what we check at each stage. The photos stay in your Proof Pack, so you can see the waterproofing after it's covered.
Step 5: Flood Testing (Tile Shower Pans)
On every Crafted Tile shower, and on any package with a tile shower floor, the pan is flood-tested: it holds water for at least 24 hours, the result is recorded with a photo in your Proof Pack, and the waterproofing/prep stage can't be closed until the latest flood test passes. A test that fails is repeated.
Why Waterproofing Is Included in Every Tile Shower
We don't price waterproofing as an "upgrade." Waterproofing isn't an optional feature — it's the structural integrity of your shower. That's why ANSI A118.10 is included in every Showerly tile shower — every Crafted Tile tier from $7,800.
We made this decision because we warrant our workmanship for 1 year, and waterproofing is the part of the shower that warranty depends on most.
What to Ask Your Contractor About Waterproofing
If you're comparing bids from multiple contractors, ask these questions:
- What waterproofing system do you use? If the answer is "we don't need one" or "the cement board is waterproof," walk away. Cement board is moisture-resistant, not waterproof.
- Will you photograph the waterproofing before tiling? If they won't document it, you have no proof it was done correctly.
- Do you use pre-formed corners and pipe seals? These factory-made pieces are far more reliable than site-applied patches.
- Is waterproofing included in your quote or an add-on? At Showerly, it's included in every tile shower — see our pricing.
Ready to discuss your shower project with a team that takes waterproofing seriously? Book a free in-home visit or ask Mat-Black, our AI agent. You can also explore our frequently asked questions to learn more about our process.