Why fresh grout can't fix what's behind the tile
Tile and grout are the finish, not the waterproofing. A U.S. Department of Energy remodeling guide calls it a myth that a tiled surround is 100% waterproof, and says the joints between backerboard, tile, the tub or shower pan and the door are where water gets in. The Building America Solution Center adds that even cement board isn't waterproof on its own: it needs a liquid waterproofing coat on its face or a water-resistive barrier behind it, and it doesn't recommend moisture-resistant "green board" behind a shower.
The DOE guide also describes a common retrofit mistake: backerboard set right down on the tub or pan, where it wicks up water that gets past the tile. Over time that loosens the tile at the base. A bottom row that keeps cracking or popping loose after regrouting points to a problem underneath.
Five checks you can do without removing anything
- Press. Push with your palm on the tiles in the lowest rows, around the valve and at the corners. Any give or a soft spot means the backing has probably gotten wet.
- Tap. Tap tiles lightly with the plastic handle of a screwdriver and compare. A dull, hollow sound over a patch means those tiles have lost their bond. National Park Service tile guidance ties loose tile to weakened mortar and says to check for loose tiles before regrouting.
- Look below and beside. After a normal shower, check the ceiling under the bathroom, the baseboard outside the shower and the other side of the wall.
- Sniff. EPA says a musty smell should prompt a closer look for hidden mold, even when nothing is visible.
- Check the soft joints. Cracks where the tile meets the tub, pan or an inside corner are usually caulk problems, not grout problems. Our grout-versus-caulk guide explains the difference.
Sort out where the water is coming from
When the stain shows up tells you which pro to call first. These patterns are a starting point, not a diagnosis:
- Wet even when nobody has showered: suspect a supply pipe or the valve. Call a plumber. You can confirm a constant leak with the water meter test.
- Wet only after water hits the walls: suspect the wall assembly, failed grout or caulk, or the door seal. A tile contractor who does shower waterproofing is the right first call.
- Wet after water pools on the floor, even from a short shower: suspect the pan or the drain connection. That usually takes both a plumber and a tile contractor.
If water is reaching the ceiling or another room, stop using the shower until it's checked. Don't pry off tiles or open the wall to look for mold yourself; EPA says investigating hidden mold can be difficult and suggests a professional with experience in water- and mold-damaged buildings. EPA also says wet materials should be dried within 24 to 48 hours to prevent mold. Wet ceiling drywall below has its own decision; see whether wet drywall can be dried or has to be replaced.
What to ask before you approve either job
For a regrout quote, ask what they checked besides the joints, and whether any loose or hollow tiles will be reset. A quote that only promises the grout will look new isn't a judgment on the wall behind it.
For a rebuild quote, ask:
- What's behind the tile now, and how much has to come out? Ask to see the damaged backing once it's open.
- What backer and waterproofing will go in: a liquid membrane on the face of the board, or a barrier behind it?
- Will the pan or membrane be flood-tested before tile goes on, and will I get photos of the waterproofing before it's covered? For one liquid membrane, USG's product sheet says it must cure about 12 to 24 hours before flood testing. Leave that test to the installer.
- Is the plumbing changing? If yes, who is pulling the permit?
Does a Philadelphia shower rebuild need a permit?
Regrouting doesn't involve plumbing, and swapping valve parts with the same material is exempt from a plumbing permit. Replacing the shower pan or drain, moving the valve or changing water or drain lines is different: L&I requires a plumbing permit for plumbing installation, alteration, replacement and repair, and a licensed master plumber must oversee the work. For a one- or two-family home, L&I lists $31 for fixture replacement with no piping changes and $37 per pipe for replacing water or waste lines, plus a $3 City and $4.50 state surcharge. Our Philadelphia plumbing permit guide covers the exemptions and inspections. Outside the city, check with your township's building office before demolition starts.