Almost everyone assumes tile keeps water out of the wall. It does not. Tile is dense and hard and it sheds most of what hits it, but the joints between tiles are porous, and grout absorbs water by nature. Some quantity of water gets past the surface in every shower, every time, in every tiled bathroom that has ever been built. That is normal and expected, and it is not what causes problems.
What matters is what happens to that water after it gets through. In a properly built shower it hits a waterproofing layer directly behind the tile, runs down that layer, and drains out at the pan, which is bonded into the drain assembly for exactly this reason. In a poorly built one it reaches wood, board, or insulation and stops there. The tile looks identical in both cases, on day one and for a long time after.
Behind the tile there should be a continuous, unbroken waterproof plane covering every wet wall, wrapping every inside corner, crossing the curb, and tying into the pan and the drain body. There are several legitimate ways to build it, and any competent tile contractor can explain which approach they use and why. The specific method matters less than the fact that it is complete and that every transition is handled deliberately.
Under that sits the substrate the tile actually bonds to, and it is not standard drywall. Wet areas call for board designed for the job, fastened correctly, with the joints treated. What lives below all of it is your framing and subfloor, which is what you are truly protecting. The whole assembly exists so that plywood and studs never find out a shower is running above them.
Flat walls are the easy part. Waterproofing fails at the transitions: the inside corners where two planes meet and move slightly with the house, the curb that is wet on three sides and gets stepped on daily, the niche that is a rectangular hole cut through the system with a horizontal shelf at the bottom of it. Every one of those needs specific detailing, and every one takes time that does not show in the finished room.
This is the part of a bathroom that separates bids. Two contractors can quote the same tile, the same fixtures, and the same layout, and build enclosures with completely different life expectancies, because one of them wrapped the corners and the curb properly and the other ran material up the flat walls and called it done. You cannot inspect the difference after the tile is set. You can only ask about it beforehand.
Water that gets behind tile does not stay where it entered. It runs down inside the wall cavity, follows framing, and surfaces wherever gravity and building geometry send it. That is why the first symptom is so rarely in the shower. It is a stain on the ceiling of the room below, a baseboard outside the bathroom that keeps pulling away from the wall, a bubble in paint on the far side, or a section of floor by the shower that gives slightly underfoot.
Inside the shower, the tells are more subtle. Tile that sounds hollow when you tap it has lost its bond. Grout that crumbles in one specific area, or a joint that keeps opening no matter how many times it is repaired, points at movement or moisture behind it. A shower that smells persistently musty even with the fan running is telling you that something back there stays wet between uses.
Open the wall in an older Wasatch Front house and the assembly behind the tile often predates modern waterproofing practice entirely. It is common to find drywall or a thin mortar bed with nothing meaningful behind it, a shower pan liner that was never turned up high enough at the curb, or a niche framed and tiled with no detailing at all. None of it was necessarily wrong when it was built. It just does not work the way current practice does.
The same demo tends to reveal neighbors of that problem: galvanized supply lines that have narrowed from the inside, venting that was undersized or improvised, and subfloor around the toilet and the tub apron that has been slowly wet for years. This is why contractors hedge before demo. Not because they are being evasive, but because the wall genuinely has not told them anything yet.
Ask each contractor to walk you through the wet area from the framing outward: what board goes on the studs, how the waterproofing is applied, how the inside corners and the curb are treated, how the pan slopes, and how the waterproofing connects to the drain. You are not looking for a specific answer. You are listening for whether they have a repeatable method or are describing it for the first time as they stand there.
Then ask what happens if demo finds wet subfloor, rot in the framing, or supply lines they recommend replacing. A contractor who has done this work has a clear process for that conversation and can tell you how it gets documented and approved. That answer tells you more about how your project will go than any photograph of finished tile ever will.
Look outside the shower first. Ceiling stains below, baseboards separating from the wall, a musty smell that lingers, or flooring near the shower that flexes are the common tells. Inside, tap the tile and listen for hollow spots, and watch for grout that crumbles in one area or a joint that reopens after every repair.
Rarely, if the waterproofing itself has failed. Surface products applied over finished tile cannot rebuild a layer that lives behind it, and they do nothing about water already in the wall. Regrouting and recaulking are worth doing as maintenance, but they are not a fix for a system that is letting water through.
Neither is automatically better. Both approaches can produce a shower that lasts decades, and both fail when the corners, curb, and drain tie-in are rushed. What matters is that the installer knows the method thoroughly and details every transition. Ask how they handle those transitions rather than asking which material is superior.
Which bathroom it is, and whether anything needs to move. That is enough to begin.
