Know Your Tiles

Porcelain Tiles

Porcelain tiles are ceramic tiles commonly used to cover floors and walls, with a water absorption rate of less than 0.5 percent. They can either be glazed or unglazed.

Porcelain has been used for making tiles for many years, only modern production methods and quantities has made the porcelain tile available for the average householder in recent years.

The dense, hard surface of porcelain has made polishing a viable alternative to a glazed surface. This means that a tile can be fired, then a polish cut into the surface, creating a shine without a glaze.

Porcelain is much harder than ordinary ceramic tiles. Specialised cements are necessary for installation of porcelain tiles Porcelain, being denser and heavier than ordinary ceramic tiles, needs a stronger adhesive to hold the weight on walls. Therefore typical ready-mix adhesives are not recommended for porcelain.

When porcelain is first made, it is not absorbent, but the polishing process for making the unglazed surface shiny cuts into the surface, leaving it more porous and prone to absorbing stains, in the same way as natural stone tiles.  polished porcelain tiles will need sealing. Porcelain sealants are either solvent-based or water-based, which is cheaper, but does not last.

Rectified Tiles

When the guy at the tile store tells you that the tile you are looking at is more expensive because it has been rectified, it sounds vaguely ominous — like someone’s been naughty and got sent to the principal’s office. Just what does he mean?

A tile that is fired at very high temperature loses most of its moisture, causing the raw tile bisque to shrink. Shrinkage is very controlled these days so that the finished size or “caliber” of the resulting tiles is very uniform — usually less than 1/16th of an inch difference from tile to tile. But, if the tile has to all be exactly the same size, it is “rectified” by cutting all the tiles to exactly the same size on a saw or grinder. This extra step adds a little to the price of the tile.

Rectified tile can be set with a very narrow grout line for a seamless look. Rectified tile is for special applications and is just not needed for most home uses, so don’t pay for it unless your tile installer insists you actually need it.

Resistance to Water

ANSI Rating: Resistance to Water Penetration

The rating developed by The American National Standards Instituted is a test of resistance to permeability by water. It consists of first boiling the tile for five hours then emersing the tile in cold water for another 24 hours and then measuring its gain in weight from the original dry state. The amount of absorption is stated as a percent of change from the dry weight.

Four ratings resulted from their studies of clay-fired tiles. These are, from lowest to highest:

  • Non-vitreous
    Water absorption of more than 7.0% by volume. Tile for non-wet areas. Around fireplaces, for example. Typically intended for walls, hobby and crafts use.
  • Semi-vitreous
    Water absorption of more than 3.0 percent, but not more than 7.0 percent. Tile for areas that may get wet on occasion, but are unlikely to see constant or standing water. Kitchen backsplashes or countertops, for example.
    A semi-vitreous tile is less porous than a non-vitreous tiles
  • Vitreous
    Water absorption of more than 0.5 percent, but not more than 3.0 percent. Virtually any indoor application including shower walls and floors. Outdoors in areas that do not freeze. (Although some vitreous tiles will pass the frost test, and can be used outdoors.
    A vitreous tile is less porous than a semi-vitreous tile because more of the tiny spaces between clay particles have been filled with glass.
  • Impervious
    Water absorption of 0.5 percent or less. Any indoor or outdoor application.
    An impervious tile is the least porous — in fact, it is essentially waterproof — but instead of calling it super-vitreous or waterproof, the creators of the test settled on impervious.

Encaustic Tiles

Encaustic tiles are ceramic tiles in which the pattern or figure on the surface is not a product of the glaze but of different colors of clay inlaid into indentations in the body of the tile. The inlays are typically 1/8 to 1/4 inch thick, and they may be composed of as many as six colors. Because of its thickness, the inlaid pattern remains as the tile is worn down over time, which makes the tiles preferred for public buildings that are heavily trafficked.

Popular in medieval times and used in a number of Gothic cathedrals in Europe until the 16th century, encaustic tiles were revived during the Victorian era and mass-produced by companies in the United States such as the the American Encaustic Tiling Company of Zanesville, Ohio, which was active until 1935.

Engobe Tile

On some tiles a thin additional layer or “slip” of clay mix called “engobe” is applied to the tile body. Engobe acts like a primer for the finish glaze coat. It is a usually light fine-grained clay which may be colored with various metal oxides to more or less match the final glaze color. This helps intensify the color of the glaze and keeps a dark tile body from showing through a lighter glaze. It is also used to fill in any minor imperfections in the tile body so the finished glaze is smoother. Very glossy tiles almost always include an engobe layer.

After the glaze is fired, a tile can be given a little polish to improve its shine. Some tiles are highly polished, a delicate operation since it is easy to cut completely through the glaze and expose the softer engobe layer which can scratch and stain easily.