I get a couple calls every month from folks here in the Austin, TX, area asking about why tiles are popping off their shower curbs. Everyone hopes that this is just a simple cosmetic problem. Unfortunately, this is almost always a leading indicator that they’ll soon need an entirely new shower. Here’s an explanation for why shower curbs leak, and why a leaking shower curb indicates failed shower waterproofing.
The Symptom
Tile and grout aren’t waterproof. Shower waterproofing happens underneath the surface tile and grout layer. That’s why badly done waterproofing will usually first show up with cracked discolored grout at the curb, especially along the seam where the outside of the shower curb meets the bathroom floor tile. That’s what happens when the 2×4 framing that forms the core of a shower curb gets loaded up with water, and then starts passing that moisture on to everything it touches.
Here are some examples:
Only one of these tiled shower curbs has surface tile that’s literally popping off. But all of them have discolored grout that shows permanent moisture underneath, and cracked grout that shows swelling. These are signs of permanent wetness underneath the surface curb tile. Usually this symptom is accompanied by other leaky shower early signs like a permanent musty smell, persistent mildew all around the shower floor perimeter, etc.
All this is a clear indication that your shower’s waterproofing is probably leaking. It’s like oil stains in your driveway, indicating that your car probably has a cracked engine block. The next definite signs will be swelling baseboard and expanding water stains on the drywall at both ends of the shower curb. Which is like ignoring your car’s accelerating oil leak ’till the check engine light starts glowing red. At that point, it’s time to stop ignoring the problem.
What Lies Beneath
Demo for shower curbs like this will reveal dryrot getting started in the wood framing that forms the core of a shower curb. And further demo for the whole shower will generally reveal more dryrot, since a leaking shower curb is a sure sign that the rest of the shower “pan” waterproofing was installed incorrectly.
The core of a shower curb is made from several 2×4 studs laid horizontally. A good shower installer will wrap the entire shower base including the curb with a continuous layer of effective waterproofing. When done correctly, this ensures that all of the shower framing including the curb never sees moisture. An effectively waterproofed shower is just that. Waterproof. A leaky shower curb shows that a shower was installed by a dope. Not waterproof.
Not Leaky Shower Curb Installs
Correctly wrapping a shower curb with an unbroken waterproofing layer requires either some knowledge of effective modern waterproofing techniquies or a lot of skill working with traditional waterproofing materials. Personally, I use Schluter Kerdi waterproofing for shower installations. This puts the waterproofing layer diretly underneath the surface tile and grout layer and is easier to flood test before tiling. However most traditional tile shower installers here in Austin still use old-school vinyl PVC liners to waterproof showers.
This is fine so long as the installer does their job to make the waterproofing liner fully seamed and actually waterproof. Problem is, wrapping a traditional PVC vinyl liner around a shower curb without punching it full of holes is a real pain in the ass. It requires using very old-school mortar skills to make a wire mesh form and concrete lathe base that you can then tile on top of.
You can’t tile on top of PVC vinyl or fiberglass. So, if you want to wrap a curb with a traditional vinyl or fiberglass liner “pan” and also want the shower install to be waterproof, then you need to wrap the curb with a layer of wire mesh and masony thinset lathe before you can proceed to tiling. But again, this requires skill. And time. It’s a pain to do traditional shower waterproofing correctly. Which is why many installers will cut corners on this step.
Leaky Shower Curb Installs
So here’s how to make an eventually leaky shower curb with traditional shower “pan” waterproofing materials. Step one, install the waterproofing liner (with maybe good seam sealing in all the corners, but probably just folded ‘cuz seam sealing is a pain) wrapped around the shower curb 2×4 framing. Then, wrap the shower curb with a layer concrete backerboard secured with screws. Then, tile on top of the concrete backerboard.
Easy peasy! Way more convenient than dealing with wire mesh and mortar lathe. And the best thing? It’ll take about five years for the screws that are all shot through the waterproofing liner to start leaking enough moisture that the homeowner’ll start to notice. So, the crappy tile shower installer will be long gone when this becomes a problem:
Shooting a traditional shower “pan” waterproofing liner through with a bunch of screwholes is like driving nails through your sailboat’s hull. The leaks won’t be noticeable for awhile, but over time (again, usually 5-8 years after the origional install) they’ll get real noticeable and start to worsen quickly.
The Fix? Start over
Obvious leaky shower curb symptoms are usually preceded by other signs of a leaky tile shower install, like persistent mildew all around the floor perimeter:
Again, tile and grout aren’t waterproof. So there’s no magic surface fix for a leaky shower. No amount of grout sealing will make grout waterproof. And trying to reinstall loose tile because the underlying wall or shower curb framing is swolen with moisture is like rearranging deck chairs on the Titanic. The only fix for a leaking tile shower install is to rip everything out and start over.
The good news? At least you can take the opportunity to get a truly custom replacement and, with some careful shopping, a new shower that will truly last a lifetime.
The other good news? Unlike leaky roofs, leaking tile shower installs usually don’t cause terrible damage very quickly. By the time moisute damage starts to show up with crumbly discolored grout around the shower curb, cracking tile on the curb, or even water damaged baseboard and drywall at the shower perimeter, the shower install will already have been slowly leaking moisture into the wall framing for years. But I’m always continually amazed with every leaky shower rebuild at how much moisture damage wall framing can take without causing any problems that aren’t easy to fix once everything is opened up to the studs.
The Bottom Line
Leaking shower curb symptoms are bad. Just like oil leaking from your car’s engine block or water dripping through your roof is bad. It’s almost always an indication that there’s gonna hafta be a whole new shower install in your future. If you have grout cracking on your shower curb or tiles getting loose, then this won’t be a cosmetic fix.
The good news? Don’t get freaked out. Leaking tile shower installs leak only a little bit of moisture with each use. It’s not gonna be catastrophic. It’s not gonna dissolve your house in black mold. Just start saving up and planning for a full shower replacement sometime within a year or so of when you first start seeing definite signs that the previous install was done incorrectly.