Are Porcelain Tiles Waterproof?

Close, not quite. Porcelain tile absorbs less than 0.5 percent of its weight in water, low enough that most manufacturers call it impervious, and low enough that in daily use it behaves like water resistant material rather than a truly waterproof one. Are porcelain tiles waterproof enough to skip a membrane behind them? No. That 0.5 percent figure describes the tile face. It says nothing about the grout lines, the edges, or the assembly holding the whole thing together, and that’s where most of the real risk sits.

Waterproof and Water-Resistant Are Not the Same Thing

Waterproof means water cannot pass through, full stop. Water-resistant means it mostly can’t, for a while, under normal conditions. Porcelain sits in the second category no matter how the marketing copy reads. ASTM C373 is the test that actually settles the question, dry weight against wet weight after a soak, and porcelain’s result lands it in the “impervious” tier, the lowest absorption bracket the standard recognizes.

Impervious is not the same word as waterproof, even though the two get used interchangeably online. A porcelain tile left sitting in standing water for months will still take on a measurable amount of moisture eventually. It just takes far longer than ceramic, stone, or anything with a higher absorption rating.

Why This Tile Resists Water Better Than Almost Anything Else

Denser clay, fired hotter. That’s most of the answer. Porcelain gets pressed from a finer, more refined clay body and fired above 1,200°C, well past what ceramic tile goes through. The heat vitrifies the clay, meaning it partially turns to glass, closing off the pores that would otherwise soak up water.

Through-body porcelain carries that same colour and density all the way through the tile, not just on a glazed surface layer. Glazed porcelain gets an extra impermeable coating baked onto the face, which pushes absorption even lower on the visible surface, though the unglazed edges and back still test at the tile’s base rate. Ceramic tile, by comparison, gets fired at a lower temperature from a coarser clay, and its absorption rate can run anywhere from 3 percent to well over 7 percent depending on the glaze quality. That gap is not marginal. It’s the difference between a tile that shrugs off a spill and one that needs real care around water.

What Happens If Porcelain Tile Gets Wet

Nothing, on the tile face itself. A spilled glass, a wet dog, a puddle by the tub, porcelain sits there and takes it without staining or swelling. That’s the whole reason it shows up in kitchens, entryways, and bathrooms across the Island.

The problem starts at the grout, not the tile. Standard cement grout absorbs water at a rate porcelain never will, and it sits in every joint across the floor. Water that pools on a porcelain floor and gets left overnight works its way into that grout, then down through hairline gaps at the perimeter, then into whatever’s underneath. We’ve pulled up porcelain floors with tile in perfect condition sitting over a subfloor that had been quietly rotting for two years, because nobody thought a waterproof-feeling tile needed a moisture barrier below it.

Long-term exposure changes the picture too. Constant standing water, a slow leak under an appliance, a shower pan that was never properly sloped, none of that stays contained by the tile alone. Porcelain’s low absorption buys time. It doesn’t buy immunity.

Is It a Good Choice for a Shower

Yes, and it’s one of the better tile choices for one. Low absorption on the tile face means less water reaching the substrate through the tile itself, and porcelain holds up to the temperature swings and constant moisture cycling a shower puts it through better than most alternatives.

The tile is never the waterproofing system, though. A shower still needs a membrane behind it, liquid-applied or sheet, installed against the substrate before the first tile goes down. Corners, the curb, and the drain area need extra attention since those are where a membrane actually fails first, not out in the flat field of tile. Coverage has to run higher than most homeowners expect too, above the showerhead, not just to shoulder height.

Floor Versus Wall Use in a Shower

Shower floors need a slip rating suited to wet bare feet, which rules out some of the glossy, highly polished porcelain that looks great on a wall. A matte or textured finish with a proper DCOF rating belongs underfoot. Walls have more room to run polished or large-format porcelain since traction isn’t the concern up there.

What Are the Real Downsides

Cost tops the list for most homeowners pricing out a project. Porcelain runs higher per square foot than ceramic, and the labour costs more too, since it’s harder on blades and takes longer to cut cleanly.

Installation difficulty comes right behind it. That same density and hardness that makes porcelain resist water also makes it resist a standard tile saw. Cutting porcelain dulls blades fast, and a rushed cut chips the edge more often than ceramic ever does. Large-format porcelain adds lippage risk on top of that, since a slightly uneven substrate shows up more on a big rigid tile than it does on a small one that can flex slightly into place.

A few more worth knowing before committing to it:

• Cold underfoot, more than ceramic or LVP, and it stays that way without radiant heat underneath
• Polished finishes get genuinely slick when wet
• Heavier than most alternatives, which matters on upper floors and older framing
• Uniform, consistent look that some homeowners find flat compared to natural stone’s variation

Rectified Edges and Grout Line Width

Rectified porcelain gets cut to a perfectly square edge after firing, which lets it sit with a much narrower grout joint than a standard cushion-edge tile needs, sometimes down to a sixteenth of an inch. Fewer grout lines and less exposed grout surface means fewer entry points for water across a shower wall or floor. It’s a small detail most homeowners never ask about, and it’s one of the more useful ones when the whole point is keeping water out of the assembly rather than just off the tile face.

Do You Need to Seal Porcelain Tile

Glazed and rectified porcelain, generally no. The glaze already seals the surface, and that near-zero absorption rate means there’s nothing for a sealer to improve much. Unglazed and textured porcelain, particularly outdoor porcelain pavers exposed to freeze-thaw cycles, benefit from a penetrating sealer even though the tile technically doesn’t need one to survive.

Grout is the part that actually needs sealing, on porcelain floors just as much as on ceramic ones. Skip it and the grout keeps absorbing water at its normal rate regardless of what tile sits next to it, which means staining, faster wear, and eventually a grout line that’s darker and rougher than the day it went in. A sealed porcelain floor with unsealed grout is only half protected, and it’s the half that was never the risk to begin with.

The Membrane Behind It Still Does the Real Work

Porcelain’s absorption rate gets treated like the whole story online, and it isn’t. Real waterproofing in a wet-area install comes from the membrane behind the substrate, not the tile sitting on top of it. That holds whether it’s a shower, a mudroom entry catching runoff off wet boots, or an exterior porcelain patio taking the coastal rain Central Vancouver Island gets most of the year.

Older homes around Nanaimo and Parksville built before membrane systems were standard practice carry more risk here than newer construction, porcelain floor or not. A gorgeous porcelain kitchen floor over a subfloor with no vapour barrier and a dishwasher connection that’s been slowly weeping for years fails the same way any other floor does. The tile just hides it longer.

A porcelain tile installation done right accounts for the membrane and the substrate prep before porcelain’s low absorption ever becomes relevant, which is really the point most of the online answers to “is porcelain waterproof” skip past entirely. Happy to walk through the specifics of your own room. Just ask us.

Frequently Asked Questions

What are the downsides of porcelain tile?

Higher material and labour cost, tougher to cut without chipping, cold underfoot without radiant heat, and a slip risk on polished finishes when wet. Heavier than most alternatives too, which matters on older upper-floor framing.

What happens if porcelain tile gets wet?

The tile face itself takes it fine, no staining or swelling. Risk sits in the grout and whatever’s underneath, since standing water left too long works into the grout joints and eventually the subfloor, regardless of how waterproof the tile feels.

Can you use porcelain tile in a shower?

Yes, it’s one of the better options for one. Choose a matte or textured finish with a proper slip rating for the floor, and still install a real membrane behind it. Porcelain’s low absorption isn’t a substitute for waterproofing the assembly.

What happens if you don’t seal porcelain tiles?

Glazed porcelain itself usually doesn’t need sealing, so skipping it rarely hurts the tile. The grout is a different story. Unsealed grout keeps absorbing water at its normal rate no matter what tile surrounds it, leading to staining and faster breakdown over time.

Related Questions

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• Are Tile Stickers Waterproof?
• Are All Tiles Waterproof?
• Are Subway Tiles Ceramic or Porcelain?
• Can Porcelain Tiles Be Polished?
• Can Porcelain Tiles Withstand Heat?

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