Porcelain and ceramic are separated by one number
Tile flooring covers two fired clay products that people use interchangeably and shouldn't. Both start as clay pressed into a shape and fired in a kiln. The difference is how fine the clay is and how hot the kiln runs, and the industry settles the argument with a water absorption test.
A tile that absorbs less than 0.5 percent of its weight in water is porcelain. Anything above that is ceramic. That is the whole definition. It sounds like a technicality until you follow the consequences: a body that will not take on water is denser, harder, immune to freeze damage, and safe in a shower, on a patio or in an unheated garage. Ceramic, being more porous, is lighter, easier to cut, kinder on your budget and completely appropriate for a dry interior floor.
There is a second split worth knowing. Glazed tile has a fired-on surface layer carrying the colour and pattern, so a deep chip shows a different colour underneath. Through-body porcelain has the same composition all the way down, so a chip is far less visible. For a commercial entrance or a busy mudroom, through-body is worth the premium.
The four numbers on the box
| Rating | What it measures | What to look for |
|---|---|---|
| Water absorption | Weight of water the fired body takes on | Under 0.5% is porcelain. Required for wet areas, exteriors and freeze exposure |
| PEI 1 to 5 | How well the glaze resists visible traffic wear | PEI 3 for normal rooms, PEI 4 for busy homes and light commercial, PEI 5 for commercial |
| DCOF | Dynamic coefficient of friction, wet slip resistance | 0.42 or higher for any interior floor that will be walked on wet |
| Frost resistance | Survival through freeze and thaw cycles | Only meaningful on porcelain. Essential for entries, patios and unheated spaces |
PEI rates the glaze, so an unglazed through-body porcelain carries no PEI number and is not weaker for it. DCOF is the one homeowners skip and regret. A polished tile looks superb and turns into an ice rink the moment someone steps out of a shower onto it.
Tile fails from underneath, not from above
Nobody has ever worn out a porcelain tile. When a tile floor fails, it cracks, and the crack came from movement in the structure below. Three conditions have to be satisfied before we set anything.
Deflection: the L/360 requirement
A wood-framed floor bends under load. Industry practice sets the limit for ceramic and porcelain at L/360, meaning the span in inches divided by 360 is the maximum acceptable deflection between supports. Over a twelve foot span, that is four tenths of an inch. Natural stone is stricter still at L/720. If the joists are undersized, over-spanned or notched badly, that gets addressed structurally, with sistered joists or added blocking, before a tile job starts. Setting tile on a bouncy floor is a guaranteed callback and no membrane rescues it.
Uncoupling and crack isolation membranes
Substrates move. Concrete shrinks and cracks as it cures and continues to move seasonally. Wood expands and contracts with humidity. Tile does almost none of that, so bonding a rigid tile field directly to a moving substrate transfers every bit of that movement into the grout and the tile.
An uncoupling membrane is a dimpled sheet that sits between substrate and mortar and lets the two layers move independently. A crack isolation membrane is a liquid or sheet product doing a similar job over an existing crack. On a slab, in a basement, over any wood subfloor, or under large format tile, one of them belongs in the assembly. On a wet floor, a waterproofing membrane goes in as well, and in a shower that is not negotiable.
Flatness, and why large tile is unforgiving
The bigger the tile, the flatter the substrate has to be. A small mosaic follows a gently undulating floor. A twenty-four by forty-eight inch plank tile spans it rigidly, and every deviation shows up as lippage, one tile edge standing proud of its neighbour. It catches toes, collects dirt and is visible from across the room under any raking light. Standard practice for large format is roughly an eighth of an inch deviation over ten feet, which is a far tighter tolerance than most floors arrive at. Getting there is patching and self-levelling work, described on our subfloor preparation page.
Most large format tiles have a slight crown, meaning the centre sits marginally higher than the edges. A traditional fifty percent brick offset puts the corner of one tile against the highest point of the next and manufactures lippage from nothing. For anything with a side longer than fifteen inches, a one-third offset or less is the standard recommendation. It is a layout decision, and it has to be made before the first tile is buttered.
How we set it
Layout first. We find the room's true centre lines, check them against the walls that people actually look at, and plan cuts so that a sliver never lands in a doorway or against the most visible wall. Dry layout costs an hour and prevents the thing you would notice every day for twenty years.
Mortar is selected for the tile and the substrate, not taken off whichever bag is nearest. Large format tile needs a mortar rated for it, with the trowel notch matched to the tile size and the ridges combed in one direction so air can escape. Every large tile gets back-buttered, a skim of mortar on the back of the tile as well as the floor, to get genuine full coverage. Coverage is checked by lifting a tile periodically and looking at it, because voids under a tile are where cracks start and where hollow sounds come from.
Movement joints go where the standards put them: at the perimeter, at changes in substrate, over existing control joints, and at intervals across large fields. They get flexible sealant, not grout. Then the floor cures before it takes any traffic, and grouting waits for the mortar rather than the schedule.
Grout is the part that fails first
Tile is inert. Grout is the maintenance item, and choosing it is a real decision.
| Consideration | Cementitious | Epoxy |
|---|---|---|
| Porosity | Porous, absorbs water and staining | Non-porous, absorbs neither |
| Sealing | Needs sealing and periodic resealing | Never needs sealing |
| Stain resistance | Moderate, and colour drifts over time in traffic | High, colour stays consistent |
| Working time | Forgiving, easy to clean up | Short pot life, unforgiving, has to be cleaned as you go |
| Cost | Low | Materially higher in both product and labour |
| Best use | Dry interior floors, large residential fields | Showers, splash zones, kitchens, commercial floors |
Joint width also matters more than people expect. Sanded grout is used for wider joints and unsanded for narrow ones, and a rectified tile with a very tight joint gives a near-continuous surface but leaves nothing to absorb variation between tiles. Wider joints are more forgiving and, in a rustic or handmade-look tile, more honest.
Where tile belongs, and where it is more floor than the room needs
Bathrooms, showers, laundry rooms, mudrooms, entries, kitchens, sunrooms and any commercial floor that takes carts, grit and mopping. Anywhere a floor has to be genuinely waterproof, tile is the only material on this site that qualifies without an asterisk. It is also the only one that is happy in direct sun, which rules it in for the exact rooms where a floating luxury vinyl plank floor gets into trouble.
What tile is bad at is comfort. It is cold unless it is heated, it is hard on legs and backs over a long day standing, it transmits sound rather than absorbing it, and anything dropped on it breaks. Bedrooms and family rooms are usually a better fit for something softer or warmer.
Heated floors are tile's natural partner
Tile conducts and stores heat well, which makes it the ideal surface over both electric mats and hydronic tubing. It also removes tile's biggest drawback in one step. If a bathroom or a basement is going to be tiled, this is the moment to decide about heat, because retrofitting it later means lifting the floor.
The assembly details still matter: an uncoupling membrane to handle thermal movement, a mortar rated for heated floors, and a slow first heat-up after full cure rather than switching the system on hard the day the grout goes in.
Living with tile
- Sweep or vacuum, then damp mop with a neutral pH cleaner. Change the water, because dirty mop water is what greys out grout.
- Keep acidic cleaners away from cementitious grout and away from any natural stone. Vinegar etches both.
- Seal cementitious grout after it has cured, and reseal on a schedule in wet rooms.
- Mats at exterior doors. Tile does not scratch easily, but tracked grit grinds into grout joints.
- Keep spare tiles from the same production run. Dye lots shift, and a replacement bought later rarely matches.
- Recaulk movement joints and perimeter sealant when they shrink or discolour, rather than grouting over them.
When we would recommend something else
If the room is a bedroom, a living room or an upstairs hallway where warmth and quiet matter, tile is the wrong tool and carpet is usually right. If you want a continuous wood look across an open plan and the wet rooms are handled separately, hardwood or a good laminate gives you that for less money and a fraction of the substrate work. And if the joists are too lively to stiffen economically, or the budget cannot absorb the prep the floor genuinely needs, a waterproof plank is a far better outcome than tile set on a substrate that was never ready for it.
The flooring comparison puts all five materials next to each other. If you already know the rooms, send us the list and we will scope the substrate work with it, because on a tile job that is most of the estimate. Our flooring installation page walks through how the work is sequenced.
Tile questions we answer most weeks
Porcelain or ceramic, what is the real difference?
Water absorption. Under 0.5 percent by weight makes a tile porcelain, above that it is ceramic. Porcelain is fired hotter from finer clay, so it is denser, harder, frost resistant and safe in showers and outdoors. Ceramic is easier to cut, costs less and is entirely suitable for a dry interior floor. It is a measured standard rather than a marketing word.
What is a PEI rating and what do I need?
PEI rates glaze wear from foot traffic on a one to five scale. PEI 1 and 2 belong on walls and in very light use. PEI 3 is fine for normal residential rooms. PEI 4 covers busy homes and light commercial. PEI 5 is for genuine commercial traffic. Unglazed through-body porcelain carries no PEI rating because there is no glaze to wear through.
Why do tile floors crack?
Movement underneath, in nearly every case. A wood floor that flexes beyond L/360 under load will break tile and grout no matter how well the tile was set, and a crack in a slab telegraphs straight up through the assembly. The answers are stiffening the structure where deflection is out of range and installing an uncoupling or crack isolation membrane so the tile is not rigidly tied to a substrate that moves.
Do I have to seal the grout?
If it is cementitious, yes, after cure and then periodically, more often in wet rooms. Epoxy grout is not porous and never needs sealing, which is why it is the right call for showers, splash zones and commercial kitchens. Epoxy is more expensive and much less forgiving to install, so it is a decision to make before the job starts rather than after.
How slippery is tile when it gets wet?
That depends on the surface, and there is a published number for it. DCOF measures wet dynamic coefficient of friction, and 0.42 or above is the accepted threshold for interior floors that will be walked on wet. Polished tiles usually sit below it. For bathrooms, entries and pool surrounds, pick a matte, textured or structured face with a stated DCOF, and a smaller format so there are more grout lines to grip.
Can tile go over an existing tile floor?
Sometimes, if the existing floor is fully bonded with no hollow tiles, the structure can carry the extra weight, and the added height still works at doors, thresholds and appliances. In most cases we recommend taking it out, because a second layer hides whatever caused the first floor to fail. Our floor removal service covers the tear-out, the dust control and the haul-away.