Floor tile is fired clay — ceramic or porcelain — or cut natural stone, set into an adhesive bed with grouted joints. It's one of the most durable, water-resistant floors available, but color and pattern tell you almost nothing about how a tile will perform. What does: a short list of ratings — PEI abrasion class, water absorption, and DCOF wet slip resistance — plus whether it's installed correctly. This guide covers those ratings, rectified vs. non-rectified edges, installation basics and why tile actually cracks, grout maintenance, and what to check before you buy.
On this page
Tile types: ceramic, porcelain & stone
Floor tile comes in three broad families. Ceramic tile is fired clay finished with a glaze — water-resistant and hard, but more porous and generally softer than porcelain, so it's best kept to walls, backsplashes, and lighter-traffic floors. Porcelain tile is fired from denser, more refined clay at higher temperatures, giving it much lower water absorption and greater hardness — the reason it dominates floors, wet areas, and heavy-traffic spaces. The two are close relatives, not opposites, and the line between them comes down to one number, covered next; for the full side-by-side see our porcelain vs. ceramic tile guide.
The third family is natural stone — marble, granite, slate, travertine, limestone, and similar quarried materials. Stone floors are unique piece to piece and can last generations, but most types are porous, need periodic sealing, and vary widely in hardness and acid sensitivity by type. Stone deserves its own dedicated guide, which we'll cover separately — treat it as a distinct material family here, not an interchangeable option.
The ratings that matter
Two tiles can sit side by side on a showroom wall and look nearly identical, then perform very differently once installed. These ratings — not the finish or color — are what actually decide whether a tile belongs on a floor, in a wet area, or under heavy traffic.
- PEI rating (surface abrasion, class I–V). Tested by rotating an abrasive load across a glazed tile's surface — ISO 10545-7 internationally, ASTM C1027 in the US — PEI grades how well a glaze resists foot-traffic wear, not impact resistance or hardness. Class I–II is for walls or very light use only; III suits ordinary residential floors; IV handles heavier residential and light-commercial traffic; V targets continuous heavy and commercial traffic. Full-body and unglazed porcelain aren't PEI-rated the same way, since there's no separate glaze layer to wear through.
- Water absorption. Measured per ASTM C373 and used by ANSI A137.1 to classify tile, this is the percentage of water a fired tile body absorbs. Porcelain is defined as 0.5% or less; non-porcelain ceramic absorbs more. Lower absorption means better resistance to staining, freeze-thaw damage, and moisture — why porcelain, not ceramic, is the default for wet rooms and any exterior or freeze-prone application.
- DCOF (Dynamic Coefficient of Friction, wet slip resistance). Tested per ANSI A326.3 (developed by the Tile Council of North America), DCOF measures how much traction a tile surface offers when wet. The published benchmark for level interior floors expected to get wet is a wet DCOF of 0.42 or greater — check this explicitly for bathroom, shower, kitchen, and entry floors, since a beautiful tile can still be dangerously slick.
- Mohs hardness (brief — and not the tile industry's real yardstick). The 1–10 Mohs scratch-hardness scale is the standard for grading natural stone, and manufacturers sometimes quote it for porcelain too — commonly cited in the 6–8 range for matte porcelain. But Mohs measures resistance to scratching by a mineral point, not the foot-traffic wear PEI actually tests, and there's no ANSI or ASTM tile standard built around it. Treat a quoted Mohs number as a rough talking point, not a spec to shop by.
Rectified vs. non-rectified edges
A rectified edge is mechanically ground to an exact, uniform size after firing, so tiles can be set with very thin, crisp grout lines. Non-rectified — sometimes called cushioned-edge — tile keeps its as-fired edge, which varies slightly piece to piece, so it needs a wider grout joint to absorb that variation. Rectified isn't a grade or quality marker; it's an edge-precision spec that mainly affects grout-line width — and because the edges are so precise, it can make minor lippage more visible if the substrate underneath isn't flat.
Installation basics — and why tile cracks
Tile is the most installation-dependent of the common floors — most tile "failures" (cracked tiles, hollow spots, loose tiles) trace back to installation, not the tile itself.
- Substrate. Tile needs a flat, stable, structurally sound base — deflection (flex) in the substrate is a leading cause of cracked tile and grout. Over wood subfloors that means adequate joist/subfloor construction plus backer board or an uncoupling layer; over concrete it means confirming the slab is flat, cured, and not transmitting excess moisture.
- Backer board. A rigid cement-based or fiber-cement panel installed over a wood subfloor, especially in wet areas, to give thinset a stable, water-durable surface — plywood alone flexes and doesn't hold thinset the way tile needs.
- Thinset. The cement-based mortar that bonds tile to the substrate. Coverage matters as much as the product: voids or gaps under a tile, from skimping on thinset or not back-buttering large-format tile, leave unsupported spots that crack or sound hollow under load.
- Grout. Fills the joints between tiles, locks them in place, and — sealed or epoxy — helps keep water from reaching the substrate. More on maintaining it below.
- Movement joints. Tile, thinset, and substrate expand and contract slightly with temperature and moisture, at different rates. The Tile Council of North America's EJ171 guidance calls for movement joints — soft, flexible joints, not grout — at perimeters, wherever the plane changes, over any expansion or control joint in the substrate below, and at intervals across large tile fields, filled with flexible sealant rather than rigid grout.
Why tile actually cracks. Tile itself is hard and largely wear-proof, so cracking almost always traces back to one of the three items above — a substrate that flexes, thinset voids leaving part of a tile unsupported, or missing movement joints letting stress build up until something gives — not to the tile's rating. A high PEI class only grades surface wear; it says nothing about structural durability.
Grout & sealing
Grout, not the tile, is the part of a tile floor that actually needs upkeep. Cement-based grout is porous, so it stains and lets moisture through unless sealed — usually periodically, more often in showers and kitchens than a dry hallway. Epoxy grout is far less porous and generally doesn't require sealing, at a higher material cost and a less forgiving installation. Either way, plan on inspecting and resealing or spot-repairing grout lines as routine maintenance: a well-installed tile floor's weak point over time is almost always the grout, not the tile.
What to look for when buying
- PEI class matched to the use — III for typical home floors, IV or V only if you genuinely have unusually heavy or commercial-level traffic.
- DCOF for any area that gets wet — ask for the 0.42-or-greater wet figure explicitly rather than assuming any floor-rated tile qualifies.
- Water absorption suited to your climate and location — porcelain (0.5% or less) for wet rooms, exteriors, and freeze-prone climates.
- Rectified vs. non-rectified edges, based on the grout-line look you want.
- Dye-lot consistency — order enough tile from the same production run, since color can shift between runs.
- Installer experience with your substrate and format — large-format tile is far less forgiving of an uneven substrate and more prone to lippage if it isn't installed dead flat.
Pros and cons, honestly
- Pros: extremely durable wear surface; genuinely water-resistant to waterproof depending on tile and installation; hygienic and easy to clean; handles heat well; doesn't fade or scratch like softer floors; wide range of looks and formats.
- Cons: hard and cold underfoot without added heat; grout needs ongoing maintenance; among the most demanding floors to install correctly; higher installation cost and skill; can still crack if the substrate moves or installation cuts corners; unforgiving to drop dishes on.
Where tile fits
Tile's water resistance and PEI-rated durability make it a natural fit for bathrooms, kitchens, entries, mudrooms, and other wet or high-traffic rooms. See our best waterproof flooring guide for how it compares with other genuinely waterproof options, and use the how-to-choose framework to weigh it against comfort, budget, and the rest of the house.
Myths & mistakes
- Myth: "Porcelain can't crack." Porcelain resists wear and water exceptionally well, but the tile itself can still crack if the substrate flexes, thinset coverage is incomplete, or movement joints are missing.
- Myth: "All tile is slip-safe because it's hard." Hardness and slip resistance are unrelated. A glossy, highly polished tile can have a low wet DCOF and be genuinely dangerous in a shower or entry.
- Myth: "You need PEI V for a home floor." PEI III already covers ordinary residential floors; PEI V targets commercial traffic most homes never see.
- Myth: "Rectified tile is a quality upgrade." Rectified is an edge-precision spec enabling thinner grout lines, not a grade or durability rating — plenty of high-quality tile is sold non-rectified.
- Myth: "Bigger-format tile is easier to install." The opposite is generally true: large-format tile is less forgiving of an uneven substrate and needs more careful, often back-buttered, thinset coverage to avoid voids, lippage, and cracking.
Frequently asked questions
What's the difference between ceramic and porcelain tile?
Both are fired clay, but porcelain is denser and fired hotter, giving it a water absorption of 0.5% or less versus ceramic's higher, more porous absorption. That makes porcelain the default for floors, wet areas, and heavy traffic, while ceramic suits walls and lighter-traffic floors. See our full porcelain vs. ceramic tile guide for the head-to-head.
What PEI rating do I need for a home floor?
PEI III is rated for ordinary residential floors and covers most homes. PEI IV adds margin for heavier residential or light-commercial traffic. PEI V targets continuous heavy and commercial traffic — it isn't required for a typical home.
What DCOF rating is safe for a wet floor?
The published benchmark for level interior floors expected to get wet is a wet DCOF of 0.42 or greater, tested to ANSI A326.3. Ask for this figure explicitly for bathroom, kitchen, and entry floors — a glossy, polished tile can fall short even if it's otherwise rated for floors.
Can porcelain tile crack?
Yes. Porcelain resists surface wear and water extremely well, but the tile can still crack if the substrate flexes, if thinset coverage leaves voids underneath, or if movement joints are missing or undersized. Hardness and crack resistance are different things — most cracking traces back to installation, not the tile's rating.
Do I need to seal tile grout?
Cement-based grout is porous and should be sealed periodically, or you can choose epoxy grout, which is far less porous and generally doesn't need sealing. Grout, not the tile, is the part of a tile floor that actually needs ongoing maintenance.
Is rectified tile a higher grade than non-rectified?
No. Rectified describes edge precision — tiles mechanically ground to an exact, uniform size so they can be set with very thin grout lines — not a quality or durability grade. Non-rectified tile simply needs a wider grout joint to absorb its natural size variation.
Sources
This guide explains standards and terms defined by the bodies below; we are not affiliated with any of them.
- ANSI A137.1 — American National Standard Specifications for Ceramic Tile: defines porcelain (0.5% or less water absorption) versus ceramic.
- ANSI A326.3 — the Tile Council of North America's standard for testing DCOF; source of the 0.42-or-greater wet benchmark for level interior floors.
- ASTM C373 / ISO 10545 — ASTM C373 is the US water-absorption test referenced by ANSI A137.1; ISO 10545-7 (with ASTM C1027 as its US equivalent) is the abrasion test behind PEI.
- TCNA — Tile Council of North America: publishes the Handbook for Ceramic, Glass, and Stone Tile Installation, including the EJ171 movement-joint guidance above.
Keep going: compare it head-to-head in porcelain vs. ceramic tile, check bathroom fit in best flooring for bathrooms, see all waterproof flooring options, or use the how-to-choose framework.
Educational information — not professional advice. Check the manufacturer’s instructions and a qualified professional before you buy or install. Last verified: 23 July 2026. See our Disclaimer & Terms.