Two bathrooms can look identical the day the last piece of trim goes on. Ten years later, one of them is still tight and the other has a soft spot in the floor outside the shower and a line of dark grout that will not come clean.
The difference is almost never the tile. It is bathroom tile waterproofing, meaning the layers behind the tile that nobody photographs and nobody ever sees again.
Tile is not waterproof
This surprises most people. Tile sheds water, and a glazed tile sheds nearly all of it, but the grout between the tiles does not. Grout is cement. Cement takes on water. In a shower that runs every day, water gets past the grout, not in a dramatic way, just steadily.
So the tile is not the thing keeping water out of your floor framing. The tile is the finish. The waterproofing lives behind it, and it is the only thing standing between a daily shower and the structure of your house.
What is actually behind a shower wall
Working from the room back toward the studs, a well built shower has the tile, the thinset it is bedded in, a waterproof layer, a solid backer for the tile to hang on, and then the framing.
The waterproof layer is either a sheet membrane bonded to the backer or a liquid coating rolled on in two passes, usually in two different colors so a thin spot is obvious. Either approach works. What matters is that the layer is continuous, up the walls, across every corner and seam, around the drain, with no gap where a fastener went through it.
Where showers actually fail
Almost never in the middle of a wall. They fail at the transitions. The inside corners. The joint where the wall meets the floor. The edges of a niche. The seam where a bench meets the wall. The ring around the drain.
Every one of those is a place where two planes meet and the waterproofing has to be made continuous by hand. The unglamorous hour a crew spends banding corners and seams is the hour that decides whether the shower lasts.
Slope, and why a flat shower floor is a problem
A shower floor has to fall toward the drain, evenly, from every direction. If it does not, water stands. Standing water finds the one weak spot it needs, and it leaves the mineral staining that makes a young shower look old.
This is also where a curbless or low threshold shower gets interesting, because the fall has to be built into the floor structure rather than sitting on top of it. That is worth settling early rather than discovering late. We lay that out under walk-in showers and tub-to-shower conversions.
Backer board is not waterproofing
Cement backer board gets described as waterproof. It is not. It is water resistant, which means it will not fall apart when it gets wet. That is a different promise. Water passes through it.
Backer board is the substrate. It gives the tile something stable to bond to and it survives the damp. The waterproofing still has to go over it, or be built into it as a bonded system. If anyone tells you the backer board on its own is enough, that is the moment to ask a second question.
Niches, benches and curbs
A niche is a hole cut into your wall in the wettest part of the room. A bench is a flat surface that collects water and meets the wall along a seam. A curb is three planes meeting at two corners. All three are lovely. All three leak if the waterproofing is treated as an afterthought.
None of that is a reason to skip them. It is a reason to decide on them before the framing goes up, while the blocking can go in and the waterproofing can be planned around them rather than cut in later.
Grout and caulk do different jobs
Grout fills the joints between tiles sitting on the same plane. Caulk fills the joints where two planes meet, so wall to floor, wall to wall, tile to tub. Those corners move slightly as the house moves, and grout, being rigid, cracks there. Caulk flexes.
If you look at a shower and see hard grout in the inside corners, it will crack eventually. That crack on its own is not a disaster if the waterproofing behind it is sound, which is the entire point of the layer you cannot see.
When a shower has already failed
A failed shower does not get patched from the front. The waterproofing is behind the tile, so reaching it means the tile comes off. Surface sealers slow water down for a while and they do not replace a membrane.
Once it is open, whatever framing or subfloor got wet has to be dealt with before anything new goes back. That is the part that makes an old shower unpredictable, and it is also the reason it is worth looking sooner rather than later. A small leak found early is a tile job. The same leak found in three years is a framing job.
What to ask, and what to look at
You do not need to know product names. Two questions get you most of the way there. What waterproofing system are you using, and can I see it before the tile goes on.
Anyone who does this properly will be glad to show you, because the waterproofed shower is the one stage of a bathroom they are quietly proud of and nobody ever sees. Take a photo of it yourself while it is open. It costs you nothing and it is the single most useful picture of your bathroom you will ever own.
Common questions
How do I know if my shower is leaking?
Soft or springy flooring just outside the shower, a musty smell that never quite clears, staining on a ceiling below, loose tiles, or grout that keeps coming out of the same spot. Any one of those is worth having looked at before the tile comes off, because the damage is usually wider than the symptom.
Does this apply to the bathroom floor outside the shower?
Less dramatically, but yes. The area around a tub and in front of a shower takes real water over the years. Carrying the waterproofing out past the shower is straightforward while the floor is open and impossible once it is closed.
Does a tub surround need the same treatment?
If it is tiled, yes. A tiled tub surround has the same corners, the same seams and the same grout. A one piece acrylic surround is its own waterproof layer, which is part of why it is simpler and part of why it looks the way it does.
Thinking about a bathroom?
Bartow Builders has been remodeling bathrooms in Manitowoc County since 1999, with our own carpenters doing the framing and the finish work. If you want a sense of how the weeks actually run, we went through it in what the weeks of a bathroom remodel look like. When you are ready, tell us about your bathroom.