Terra cotta means "baked earth" in Italian. More precisely, terra cotta is fired clay. Terra cotta has been used as a floor tile for thousands of years, especially in countries around the Mediterranean Sea. There is little difference between terra cotta flooring materials. Natural colors range from dark brown through ocher to brick red and are the result of the clay's chemical makeup and the way the clay is fired. The color of traditional terra cotta floor tile is orange red because iron in the clay burns red when oxidized. Some terra cotta tiles are "flashed," that is, exposed to varying temperatures, to create a mottled appearance.
Some terra cotta flooring materials have different physical properties, resulting from the type of clay and method of manufacturing. Clay tile fired at lower temperatures is more permeable and softer than tile fired at higher temperatures, which create a more vitreous (glasslike) and hard-wearing flooring material. Keep in mind that porous tiles absorb moisture more readily and therefore stain more easily.
Machine made unglazed quarry tile are manufactured by extrusion; forcing the clay through a die. Before curing and firing, the clay sometimes goes through a vacuum chamber to draw out any air bubbles. It can be difficult to tell some machine made tiles from hand-molded ones. The tip-off is a precisely scored back, a result of the extrusion process. Also, machine-made tiles are generally harder, denser, and more durable.
Machine made, glazed tiles are smoother, and usually shinier, than unglazed ones. Glaze is a thin, glassy coating bonded to the clay at a very high temperature in the kiln, producing a hard finish. Surface textures range from high-gloss to mat and pebbly. Even tiles with a rough texture are prone to slickness when wet, so experts advise against using glazed terra cotta tiles outdoors. Glazing makes tiles more stain resistant, and there is no need to seal them.
Think about whether the tile you like is actually best suited to the job you want it to do. Softer terra cotta tile can fracture and crumble at below-freezing temperatures. When considering terra cotta tiles, ask about strength, usually calculated in pounds force and absorption rate, a calculation of how much moisture the tile absorbs. High breaking strength and low absorption rates offer the best durability.
All unglazed tiles and cement based grouts need sealing. Some unglazed terra cottas floor tiles are sealed at the factory; unsealed unglazed tiles should be sealed with a penetrating sealer which allows the tile to breathe after installation. Sealers may darken the tile's surface or give it a shiny appearance.
After sealing, unglazed tile floors may be waxed and buffed for additional protection and a glossy look. Routine cleaning involves washing with warm water and a mild detergent. Avoid bleach products; they can draw the color out of colored grouts. All unglazed tiles need to be resealed periodically.