Ceramic tile

A ceramic tile is two materials pretending to be one. Underneath there is a fired clay body that is still full of tiny voids. On top there is a skin of glass, melted onto that body in a kiln, thin enough that a chip goes straight through it to the biscuit underneath. The glass is hard, watertight and any color a chemist can make. The body under it is none of those things. Once you can see the tile as a skin over a sponge, the rest of it stops being mysterious.

A soft body under a hard skin

The body starts as clay, either pressed dry in a mold or squeezed out and cut. It goes through a kiln hot enough to fuse the particles into something rigid, but not hot enough to close the gaps between them, and those gaps are what make ceramic ceramic. Glaze is then floated or sprayed on as a liquid slurry and fired, sometimes in the same pass and sometimes in a second one. A second firing is what allows the deep, glassy, decorated surfaces you see on a handmade looking wall tile.

How open the body stays gets measured and banded. ANSI A137.1 calls a tile impervious at 0.5 percent water absorption or below, vitreous above that up to 3.0 percent, semi vitreous above 3.0 up to 7.0 percent, and non vitreous above 7.0. Porcelain lives in the first band by definition, which is the whole of that argument. Most wall ceramic lives in the last two, and it is perfectly good tile there, because nothing on a wall is asking the body to do anything.

The body also sets a practical ceiling on format. A large tile has to survive being carried, set and then walked on across a span, and a more open body has less to give on all three counts, which is why the very large field tiles and the long plank formats are almost entirely porcelain. Ceramic tends to arrive in sizes a person can handle comfortably in one hand on a ladder. That is not a rule anyone wrote down. It is what the material can do, showing up in a catalog.

What the softer body buys you

Openness is not only a weakness. A more porous body is lighter, which matters on a vertical surface where every tile is hanging off thinset instead of sitting on a floor. It cuts with a score and snap rather than a wet saw, so an installer working around outlets, a window return or a run of cabinet uppers moves faster and wastes fewer pieces. It takes trim shapes readily, so bullnose, pencil liners, chair rail and inside corners actually exist in the line rather than being something you improvise.

The glaze palette is the other half of it. Because the body is not doing the visual work, the surface is free to be a crackle, a hand painted look, a thick gloss with real depth, a subtle tonal shift down a subway wall. Those effects tend to live on ceramic. This is why a backsplash rack and a floor rack in the same store look like they came from different industries.

The failure mode always starts at the glaze

Ceramic almost never fails in the middle of the body. It fails where the glass gets interrupted. Drop something heavy on a ceramic floor tile and the chip shows a pale biscuit under a colored surface, and from standing height that light spot reads as damage in a way a scuff never does. Drag grit across a traffic lane for a few years and the gloss dulls along the path people walk, so the floor develops a road through it while the corners still look new.

Two smaller ones are worth knowing. Crazing is a network of hairline cracks in the glaze itself, a stress pattern rather than a break, and on some decorative tiles it is deliberate. And once the glass is breached anywhere, the body behind it can take on water and hold it, which is how a stain appears to come from under the surface. None of this is an argument against ceramic. It is an argument for putting ceramic where the glaze is not being attacked.

Where ceramic is the right answer

Walls, first and mostly. Backsplashes, shower walls, tub surrounds, a laundry wall behind a sink, a fireplace face. Nothing walks on any of them, the glaze is only asked to shed water and wipe clean, and the color range is wider than anywhere else in tile. Ceramic also holds up fine on a floor that is genuinely low traffic, a powder room or a guest bath at the end of a hall, provided the abrasion class on the tag suits the room. That class is the check that separates a wall tile from a floor tile, and the PEI entry explains how to read it.

Where it is the wrong answer is equally clear. An entry or a mudroom taking road salt and grit off a driveway all winter is a glaze grinder. A kitchen work lane in front of a sink is the same in slower motion. A shower floor is a wet grip question before anything else. In those rooms the denser family earns its place, and the tile overview lays out how the house usually divides.

How to check a ceramic sample before it is ordered

• Read the tag for a wall only marking or an abrasion class. A tile intended for walls will often say so plainly, and that sentence outranks any opinion about how tough it looks.
• Look at a cut edge to see the body color under the glaze, then decide how you would feel about a chip that size in that room.
• Hold the sample at a low angle to a window. Glaze gloss and any waviness show up under a raking light and vanish under an overhead one.
• Ask whether the line carries the trim pieces you will need. Finding out at install that a bullnose was never made is a bad afternoon.
• Ask what joint width the tile wants, because a pressed edge needs a wider joint than a cut one, and the joint drives which grout goes in it.

Every one of those needs the tile in your hand, which is the argument for settling it in the showroom rather than from a photograph. Call 636-332-0654 and tell us what surface you are covering, or walk in and say it at the rack, and we will tell you exactly what you are holding and whether the tag suits the room.