This is a very common question we get on Cape Cod, and it is the right one to ask before anyone picks up a grout tool kit. Regrouting a shower that is actually leaking behind the tile wastes your money and hides the problem for another year. Here is how to tell which one you have.
Start with what grout can and cannot do
Grout is cement. It is porous, it absorbs water, and it was never the waterproofing layer. In a correctly built shower, water that soaks through the grout hits a membrane behind the tile and drains back out. So "bad grout" by itself does not cause a leak. What it does is let more water reach whatever is behind it faster. If that layer is sound, you have a grout problem. If it is not, you have a leak, and the grout is just where you noticed it.
Signs it is only the grout
- The grout is cracked, crumbling or missing in spots, but the tiles around it are solid when you tap them.
- Dark or stained grout cleans up and stays clean for months.
- The caulk at the corners and at the tub or pan has pulled away or gone moldy, but nothing is soft or stained behind it, or around the curb.
- The shower is fully dry by the next morning.
- No smell, no stain on the other side of the wall, nothing on the ceiling below.
In that case, the fix is topical: remove the failed grout, regrout, replace the caulk joints, seal. About a day and half of work.
Signs it is a leak
- Grout stays dark or damp-looking long after the shower dries, especially in one area: the floor, the first row of wall tile, a corner, or around the drain.
- Tiles sound hollow or feel loose.
- A white, chalky crust on the grout lines (efflorescence). That is minerals carried to the surface by water moving through the assembly.
- A musty smell that cleaning does not remove.
- Peeling paint, a stain or a soft spot on the ceiling below, on the wall behind the shower or around the curb just outside the shower.
- Swollen baseboard or a buckled floor just outside the curb.
- Mold on the grout that keeps coming back no matter how often you bleach it.
One of these alone can have another explanation. Two or more together usually mean water is where it should not be.
A quick test you can do yourself
Clean the grout, then stop using that shower for 48 hours with the fan running and the door open. If everything dries evenly, the room was not drying out and the grout was the only issue. You’re due to fix your bathroom’s ventilation device. But if one patch is still dark after two days, water is feeding it from behind. For the full version of this test, read our post on grout that stays wet and will not dry.
Where a leak usually comes from
- The pan. A failed or missing liner, a liner not connected to the drain's weep holes, or no pre-slope, so water sits in the mortar bed under the floor tile.
- The curb. Wood curbs that were never wrapped, or a liner that was nailed through.
- Corners, niches and benches. Wherever the membrane had to be cut and lapped.
- Plumbing. The valve, the arm, or the drain connection (This one is not a tile problem, and you want to know before you spend money on tile).
How we settle it without tearing anything out
We run a multi-factor leak test that treats this exact question as the goal. A 12-question interview, a photographed walk-through of every red flag, a knock test on the floor and lower walls, a 22-point pin moisture map compared to a dry reference point in your house, thermal imaging, and a bucket test that separates plumbing from waterproofing. The combination of all of that produces one of four answers: plumbing leak, waterproofing failure (tile system), slow leak, or no leak. You get a written report the same day.
It costs $399 + fee according to the distance of the job site, per bathroom, credited toward the repair, and includes a free estimate for whatever the fix turns out to be. If it is only the grout, the report says so and we regrout it.
Schedule a shower evaluation or call (774) 368-9592. We serve Cape Cod, Martha's Vineyard, Nantucket and Plymouth County.
Not sure if your shower is leaking?
Our multi-factor leak test finds the answer in one visit without removing a tile: interview, photographed inspection, knock test, 22-point moisture map, thermal imaging and a bucket stress test, with a written diagnosis the same day. $299 per bathroom, credited toward the repair. Serving Cape Cod, the Islands and Plymouth County.