Porcelain vs ceramic tile: the one number that decides it

Porcelain and ceramic come out of the same kind of kiln and, sitting side by side on a display, look like the same product at two prices. The difference is one number on the technical sheet, and that number decides whether the tile survives an unheated Canadian entryway or blows its face off in the third winter.

The dividing line is water absorption

The industry definition is simple and it is a measurement, not a marketing word. A tile is porcelain if it absorbs 0.5% or less of its own weight in water, tested by the boil-and-vacuum method behind ASTM C373 and referenced by ANSI A137.1. Non-porcelain ceramic is anything above that line — typically a few percent for floor tile, and well into double digits for some wall tile.

That density comes from finer clays, pressed harder and fired hotter. A denser body is stronger — ANSI sets a minimum breaking strength of 275 lbf for porcelain floor tile — takes on water only at the surface, and does not care what the temperature does.

Ceramic’s porosity is not a defect. It is why ceramic is lighter, cheaper, kinder to a tile cutter, and entirely appropriate on a wall or a dry interior floor. The mistake is not buying ceramic; it is buying ceramic for a place that freezes.

Frost is the case that actually breaks tile

Water expands by roughly 9% when it freezes. In a body that holds water in its pores, that expansion has nowhere to go and it pushes the face off the tile — spalling. It does not happen in one night; it happens over a few dozen freeze-thaw cycles, which is one or two Canadian winters.

• Unheated or exterior spaces: a detached garage, a workshop, a three-season porch, exterior steps, or a cottage sitting at −25 °C from December to March. Porcelain, and check the manufacturer actually states frost resistance rather than assuming it from the word on the box.
• Frost resistance belongs to the assembly, not just the tile: an exterior-rated mortar, movement joints, and somewhere for water to drain. A frost-resistant tile over a substrate that stays saturated still fails — the tile survives and the bond does not.
• Heated entryways are a different problem: not frost, but constant wet, grit and road salt working into every grout joint all winter. Porcelain, a dense grout, and a mat long enough that two full steps land on it.

PEI is a glaze rating, and only that

The PEI scale measures how well a glazed surface resists abrasion. It is not a strength rating, it is not a scratch-proofing promise, and it does not exist for unglazed tile — a through-body porcelain with no PEI number is not a lesser product, it simply has no glaze to grade.

What wears a glaze is grit, not footsteps. A doormat and a habit of taking boots off does more for a floor than moving up a PEI grade.

Through-body, colour-body, glazed

• Glazed: the decoration is a layer on top of the biscuit. Chip it and you see the body underneath — usually white or tan, and obvious. Nearly all wood-look and marble-look tile is glazed porcelain with an inkjet-printed face.
• Colour-body: the biscuit is tinted to roughly the glaze colour, so a chip is far less visible. A sensible middle option in an entry.
• Through-body: the pattern runs all the way through, so chips and wear are nearly invisible. It is the commercial default and the honest answer for a garage or workshop floor.

Two things to ask about any printed tile. How many faces are in the print run — a wood-look with only six or eight will visibly repeat, and the fix is to dry-lay from several boxes at once. And the shade variation code on the box: V1 is uniform, V4 is substantial variation, and a V4 tile nobody warned you about is the most common “this is not what I ordered” call in the trade.

Cutting it, and why the labour cost is different

• Ceramic scores and snaps on a manual cutter for most straight cuts, and a modest wet saw handles the rest. It is genuinely DIY territory.
• Porcelain is dense and unforgiving. It needs a wet saw with a good continuous-rim diamond blade and a slow feed, and a worn blade chips the glaze on every single cut. Holes for a toilet flange or a shut-off valve need a diamond hole saw run wet, not a carbide bit.
• Large format — a side of 15 in (380 mm) or more — is its own trade. The tile is flatter than your floor, so every deviation shows as lippage. Expect a flatness requirement near 1/8 in over 10 ft, a large-format mortar, back-buttering, levelling clips, and a running-bond offset of no more than a third of the tile rather than a half, because most large tiles crown slightly down the middle.
• Both need a stiff floor. The usual limit for ceramic and porcelain is L/360 deflection; natural stone is stricter at L/720. Over a cracked slab or a marginal wood subfloor, an uncoupling membrane is the difference between a floor and a repair bill.

Budget for that difference. Porcelain is heavier to carry, slower to cut and harder on blades than the same layout in ceramic — none of which shows up in the price on the box, and all of which shows up on the invoice from your tile setter.

Slip resistance and grout — the two things people notice later

Slip resistance has a real measurement behind it: DCOF, under ANSI A326.3, where 0.42 is the usual minimum for a level interior floor expected to be walked on when wet. Aim higher for an entry or a shower floor. This is where polished porcelain earns its regrets — a high-gloss floor inside a Canadian front door, with wet boots and melted snow on it, is a hazard however good the photo looked. A small-format mosaic on a shower floor gets most of its grip from the grout lines, which is why it is still the standard there.

Grout deserves more thought than it gets, because every joint is the porous part of an otherwise dense floor. Rectified tiles are machined to a consistent size and allow a tight 1/16–1/8 in joint; un-rectified tiles need a wider one to absorb the size variation from firing. In an entry that sees road salt, a high-performance or epoxy grout costs more in labour and pays it back, and a grout sealer is the cheapest thing you will buy for that floor.

What our catalogue can tell you, and what it can’t

Our flooring lines include 10,898 tile products that carry a price, and the median tile listing is $111.70.

That count is the Tiles category as suppliers file it. It does not separate porcelain from ceramic, and it says nothing about glazed versus through-body. Water absorption and the PEI rating are product-level facts: where the manufacturer publishes them, they are in the spec table on the product page, and where they are not, ask us and we will go to the technical sheet before you commit to a room.

The median is per listed unit as well, which in tile is unusually misleading — a box of 24×24 porcelain and a box of 4×12 wall tile can cost the same and cover wildly different amounts of floor. Divide by the coverage on the carton every time.

Ordering: waste, lots, and weight

1. Measure, then add 10% for a straight layout and 15% for a diagonal or a herringbone. Add more again for a room full of jogs, niches and doorways — every one of them is a cut.
2. Order the whole job in one go and check the shade and lot codes on the boxes when they arrive. Tile from a different run is a different tile.
3. Keep a spare box somewhere dry. A cracked tile in year four is a twenty-minute repair if you have a match, and a much bigger conversation if you do not.
4. Remember that tile is heavy. A box of large-format porcelain is a two-hand lift and a full floor’s worth moves on a pallet, so weight drives what the freight costs.
5. Plan the substrate before the tile: membrane where it is needed, the right mortar for the format, and movement joints where the standard calls for them.
6. Order samples and put them on the actual floor, in the actual light. And if one has to come back: 30 days, unused and in the original packaging, a 15% restocking fee may apply once the refund assessment is complete, and return shipping is yours to pay — which, with something as heavy as tile, is the most expensive version of that sentence in the store.

Shop what this guide covers

• floor tiles — where the absorption number and the DCOF figure actually matter.
• wall tiles — the place a porous ceramic body is the right answer.
• mosaic — the shower floor, where the grout lines are doing the gripping.
• grout, tile and grout sealers and setting materials — the porous half of a dense floor, and what bonds it down.
• tile edge trims — how the tile finishes at a doorway, a step or an outside corner.
• tile spacers and installation tools — spacers, levelling clips and diamond blades.