When a shower starts leaking, most people blame the grout or the caulk. In our experience remodeling bathrooms across Greater Boston, those are often not the real problem. The failure is in the shower pan — the waterproof assembly underneath the tile that you never see until we open it up.
Here is what we typically find under the tile in older homes, and why surface fixes don’t work.
Lead pans: the old way
Houses built from the 1920s through the 1960s often have sheet-lead shower pans. Over decades the lead corrodes and cracks — usually at the folds around the drain and the weep holes. Once a crack opens, water doesn’t drip straight down; it travels. It soaks the mortar bed, runs along the subfloor, and shows up as a stain on the ceiling below, or as rot where the studs meet the floor. By the time the leak is visible, the lead pan has usually been leaking quietly for years.
Mortar-bed and vinyl-liner pans: the usual suspects
Many homes from the 1970s onward have mortar beds over a vinyl liner. These fail in different ways, but they fail a lot:
- Nail and screw punctures. Fasteners driven through the liner to hold backer board or tile edge are one of the most common leak paths we see.
- Clogged weep holes. Mortar dams around the drain block the weep holes that are supposed to let the pan drain under the tile. The bed stays saturated, and that standing water wicks into the walls.
- No real slope. Some pans were floated nearly flat. Water should travel downhill under the tile at the same pitch you feel under your feet. When it doesn’t, the bed holds water permanently.
- Liner seams and corners. Vinyl liner folds at corners and seams are easy to cut too tight or leave stress-folded. These open slowly, and they only open up under water — invisible during a casual inspection.
What the demo actually reveals
When we remove a failed pan, the picture is consistent: a dark, waterlogged mortar bed that crumbles; subfloor plywood that is soft and blackened; studs and sill plates with rot or mold where the pan met the wall. Sometimes the drain flange itself is corroded through. The tile above can look fine — tile is a wear surface, not the waterproofing. That’s the part most homeowners find surprising.
Why refinishing or reglazing can’t fix it
A failed pan is a failure of the waterproofing assembly and the structure under it, not of the surface you see. Refinishing puts a new coating on top of the tile; it does nothing about water trapped in the mortar bed, nothing about a punctured liner, and nothing about a pan that never had slope. At best it seals the visible surface while the rot underneath continues. Many of the pans we rebuild had, at some point, been “sealed” or recaulked as a fix. It buys time; it doesn’t buy a fix.
How a rebuild should go
The only real repair is to strip the shower down to the framing and build the pan assembly correctly: continuous pan liner with turned-up edges, a mortar bed with true slope to the drain, walls on cement board with a full waterproofing coat at every corner, niche, and penetration — then tile, last. We documented exactly that rebuild sequence for a Newton walk-in shower in our Layer by Layer article — that piece is the “what a proper build looks like” companion to this one.
If your shower has a musty smell, loose tiles near the base, efflorescence on the grout, or a stain on the ceiling below, the problem is most likely under the tile — and the sooner it’s opened up, the less rot there is to repair. A free in-home estimate can tell you what’s actually down there.
Sun Shore Construction is a licensed and insured remodeling contractor serving Greater Boston. Credentials available on request.
