Are All Tiles Waterproof?

No. Some tiles get close enough that it doesn’t matter in practice, and some soak up water like a sponge with a glaze painted over top. The tile you pick is only half the answer anyway. Grout, membrane, and how the whole system was installed decide whether water actually stays where you want it, on the surface and nowhere else.

The Short Answer

Porcelain tile has a water absorption rate under 0.5%, which industry standards treat as functionally waterproof. Ceramic tile runs 3% or higher depending on the glaze and body, water resistant but not impervious the way porcelain is. Natural stone, if it’s unsealed, can sit anywhere from 3% to 20% absorption depending on the type. Marble and travertine are the thirstiest of the common choices.

None of that matters much if the grout lines are dry and cracking, or if there’s no waterproof membrane behind the wall. We’ve pulled tile off Island bathrooms where the porcelain itself looked perfect and the plywood behind it was black with rot. Right tile, wrong waterproofing underneath.

Water Absorption Rates: Porcelain vs Ceramic vs Natural Stone

Porcelain gets fired at a higher temperature than ceramic and uses a denser, more refined clay body. That density is what pushes absorption below 0.5%. ASTM classifies anything under that threshold as impervious. Practically speaking, porcelain that gets splashed or sits wet for a stretch isn’t pulling moisture into the tile body itself.

Ceramic runs a coarser, less dense mixture fired at a lower temperature. The glaze on top does most of the water-resisting work. Scratch or chip through that glaze, and the unglazed body underneath will absorb moisture over time. That’s why we steer clients toward porcelain for shower pans and other constantly wet floors, and save glazed ceramic for walls and backsplashes where standing water isn’t the issue.

Natural stone is its own category entirely. Granite is fairly dense. Marble, travertine, and limestone are porous enough that they need a penetrating sealer before grout even goes in, and again on a maintenance schedule after. Skip that step and stone stains from the first spilled glass of wine.

The Tile Isn’t the Waterproof System

Grout Is the Weak Point

Grout is cement-based and porous by nature, full stop. Standard sanded or unsanded grout will let water through the moment it’s left unsealed, and even sealed grout needs resealing on a schedule, usually every one to two years in a shower. Epoxy grout skips this problem since it doesn’t absorb the way cement grout does, though it costs more and handles differently during install. Either way, the grout lines are doing more of the water-holding work than most homeowners assume, not the tile itself.

The Membrane Is the Real Barrier

Behind the tile and grout, in any wet area worth the name, there needs to be a waterproofing membrane. Sheet membrane, liquid-applied membrane, or a properly built mud-set system with a waterproof layer built in: one of these has to sit between the tile assembly and the framing. That layer is what actually stops water from reaching the subfloor or wall studs. Tile and grout slow water down. Making the whole assembly waterproof is that layer’s job, not theirs.

This is the part every one of the sources we checked circles back to eventually, and it’s the part most homeowners skip past on their way to picking a tile colour.

Where a Membrane Actually Matters

Full wet rooms first: showers, tub surrounds, steam rooms. No debate there, a membrane is non-negotiable regardless of tile choice. Bathroom floors outside the shower footprint need one too if there’s any chance of standing water, a kids’ bathroom especially.

Kitchen backsplashes and dry-area bathroom walls sit at the other end. Splashes and steam, not standing water, so a moisture-resistant backer board without a full membrane system is usually enough. We still recommend a membrane behind any tile near a kitchen sink or a laundry hookup, since a slow supply-line leak behaves exactly like a shower failure over time, just slower to show itself.

Traditional Mud-Set vs Modern Membrane Systems

Older Island homes, plenty of them built through the 70s and 80s, used a traditional mud-set shower pan: a mortar bed poured over a hot-mop tar membrane or a CPE liner, sloped to the drain, then tiled directly on top. Done right, that system lasts decades. We’ve opened up 40-year-old showers with a still-intact liner underneath.

New builds and most renovations we do now use sheet membranes (Schluter Kerdi and similar systems) or liquid-applied membranes painted directly onto cement board. Faster to install, easier to inspect before tile goes on, and they bond directly to the backer board instead of relying on a mortar bed to hold shape. Either method works. What fails is skipping the membrane step entirely, or trusting a thin-set mortar to do a membrane’s job.

How to Test Tile You Already Have

Drop a few drops of water on a dry, unglazed edge or the back of a leftover tile from the same batch. Absorbs within a minute or two, that’s ceramic or a porous stone. Beads up and sits there, likely porcelain or a sealed, low-absorption tile. Not a lab test, but it tells you more in thirty seconds than guessing off the box the tile came in years ago.

For tile that’s already installed and grouted, the water-drop test on the field tile itself won’t tell you much, since the glaze covers most of the absorbing surface anyway. What matters more at that point is the grout line. Run a finger along it after it’s been dry a day. Chalky, crumbly, or visibly darker than when it was installed: sealer’s worn off, and that’s the part actually letting water through now, not the tile.

Cost of Fixing a Failed Waterproofing System

Resealing grout on an existing shower runs cheap, usually a half-day job and mostly labour, and it’s the fix we recommend trying first if the tile itself looks sound. Once water’s actually reached the membrane or the substrate behind it, the job changes completely. That means opening a wall or floor section, which on a standard shower surround puts a full re-tile back on the table, membrane and all.

The gap between those two numbers is the whole argument for catching this early. Call about a musty smell or a soft spot early, and it’s usually a resealing quote. Wait until the drywall on the other side of the wall is visibly stained, and it’s a demolition quote instead, one where the tile choice barely factors into the final cost anymore.

Mistakes That Let Water Through

Skipping the membrane tops the list, already covered above. After that:

Wrong adhesive or grout for the application. Standard thin-set on a submerged tile application, or the wrong grout type for the joint width, both invite failure faster than the tile itself will ever show.

Unsloped shower floors. Water needs somewhere to go. A flat pan holds standing water against the grout lines indefinitely, which accelerates every other failure on this list.

Never resealing grout. Sealer wears off. Nobody notices until the grout starts darkening or the caulk line at the tub separates.

Unfinished edges and corners. Where tile meets tub, meets a niche, meets the floor: those transitions need proper caulk or trim, not just grout pushed into the gap and hoped for.

Best Tile for Wet Areas

Porcelain wins for shower floors and pans as the most waterproof option, full stop, for the absorption reasons above. Glass tile is genuinely waterproof at the tile level too, since it’s non-porous by nature, though it needs careful setting since it shows trowel marks and thinset colour through the surface.

Ceramic works fine for shower walls above the splash zone, and for backsplashes and bathroom floors outside the wet footprint. It’s the budget-friendlier choice and holds up well anywhere it isn’t sitting in standing water on a regular basis.

Natural stone can go in a shower, but plan on a sealing schedule from day one, and expect the softer stones (travertine, some limestones) to need more frequent attention than porcelain ever will. Not the tile we’d recommend for a low-maintenance rental bathroom.

What Happens When Waterproofing Fails

Mould behind the wall is the first sign, usually smelled before it’s seen. Soft spots in the subfloor or a spongy feel underfoot come next if it’s a floor. On the coast, with the rain load Nanaimo and Victoria get through the winter, a failed membrane in an exterior wall assembly compounds fast, since the moisture has nowhere dry to migrate toward.

We get called out most often for a grout line that’s darkened and started smelling musty, or a baseboard that’s soft near a bathroom. By the time either shows up, the membrane’s already been compromised for a while. Catch it early and the fix is opening one section of tile. Wait it out, and the whole wall or floor assembly comes out instead.

Can Tile Be Left Outside

Depends on the tile and the climate. Porcelain rated for exterior use, with a proper frost rating, handles Island winters fine on a patio or entry. Standard interior ceramic doesn’t, since freeze-thaw cycling gets into any moisture the tile has absorbed and pops the surface apart from the inside. Natural stone left exposed weathers, stains, and can spall the same way over a few winters if it wasn’t rated and installed for outdoor use.

Anyone tiling a covered porch or an outdoor kitchen counter on the Island should ask specifically for porcelain rated for exterior freeze-thaw and true low absorption, not whatever waterproof-sounding tile is left over from an interior job. Some of this only gets settled once somebody has seen the actual room, so talk to us first.

Frequently Asked Questions

How to tell if tile is waterproof?

Check the water absorption rating on the spec sheet. Under 0.5%, that’s impervious-grade porcelain. Above 3%, standard ceramic, water resistant but not impervious. No rating listed, ask the supplier before it goes in a wet area.

What tiles should not be used in a shower?

Unsealed natural stone with high absorption, and unglazed or low-fire ceramic meant for decorative use only. Anything without a slip rating for wet floors either, regardless of how waterproof the tile body itself is.

What type of tiles are waterproof?

Porcelain, at under 0.5% absorption, and glass, since it’s non-porous by nature. Both still need proper grout and a membrane behind them to make the whole assembly waterproof, not just the tile face.

Is porcelain tile 100% waterproof?

Close, not absolute. Under 0.5% water absorption counts as impervious by ASTM standard, but that’s a rating on the tile body, not a guarantee on the finished install. Grout and membrane still carry the rest of the job.

What are the downsides of ceramic tile?

Higher water absorption than porcelain, a glaze that can chip and expose the porous body underneath, and generally less durable underfoot in high-traffic wet areas. Cheaper and easier to cut, which is the trade-off.

Are ceramic tiles ok for showers?

On walls, yes, especially above the splash zone. Shower floors and pans are where porcelain earns its keep instead, given the absorption difference, though a lot of older Island bathrooms were tiled in ceramic throughout and held up fine with good grout maintenance.

What type of tile is most water resistant?

Porcelain, by a clear margin over ceramic, with glass tile close behind since it doesn’t absorb water at all. Natural stone trails both unless it’s kept sealed on a strict schedule.

Does water go through ceramic tile?

Through the intact glazed surface, barely any gets through at all. A chip in that glaze, or the unglazed body beneath it, tells a different story, letting water in gradually over time. That’s the gap porcelain closes and ceramic doesn’t.

Is it okay if tiles get wet?

Fine, that’s what tile in a bathroom or kitchen is built for. The concern isn’t a wet tile surface, it’s standing water sitting on unsealed grout or pooling on a flat, unsloped floor for hours at a stretch.

Can tiles be left outside?

Porcelain rated for exterior freeze-thaw handles it. Standard interior tile doesn’t survive an Island winter’s freeze cycles without cracking or spalling.

How do I make my tiles waterproof?

Start with porcelain or glass for anything wet. Seal the grout on a schedule, roughly every one to two years in a shower. Make sure there’s an actual membrane, sheet, liquid-applied, or a proper mud-set system, behind the tile before any of the finish layer goes on. Skip any one of the three and the “waterproof tile” claim only covers part of the job.

Not sure what’s behind your existing tile, or planning a new bathroom tile installation? Worth a look before the grout starts telling you there’s a problem. Most of our porcelain tile jobs start with exactly that conversation.

Related Questions

• Are Porcelain Tiles Waterproof?
• Are Bathroom Tiles Waterproof?
• Are Tiles Ceramic?
• What Is Daltile?
• Can I Use Schluter ALL-SET for Tile?

Jordan Tile & Stone

Tile installation and repair across central Vancouver Island: Campbell River, Courtenay, Comox, Oyster Bay, Nanoose Bay, Parksville, Qualicum Beach and Nanaimo.

Phone: (250) 201-3891
Hours: Monday to Sunday, 7:00 am to 6:00 pm
Address: 4423 Patricia Rd, Oyster Bay, BC V9H 1B8