Some tiles make an excellent choice for outdoor applications. Others fail because they either cannot endure the weather or they do not provide a safe surface on which to walk. Ceramic tile manufacturers use rating systems for factors that indicate whether a tile is appropriate for outdoor applications. Some tile materials, such as cement, stone or quarry, do not display the rating information as it only applies to ceramic and porcelain. These nonceramic tiles benefit from an application of sealant to protect them from moisture absorption when used outdoors.

Wet Patio
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Outdoor tiled patio being rained on

Tile Wear Ratings

The Porcelain Enamel Institute has a rating system for tiles. The system assesses tiles for hardness and durability, and ranks them on a one through five scale. These rankings only apply to glazed ceramic tiles, which includes porcelain. Grades one through three indicate tiles for light to medium traffic areas or indoor applications, such as kitchen counters or bathroom floors. Grades four and five are tougher tiles able to withstand plenty of traffic in residential or commercial applications. Grade four and five tiles are suitable for use outdoors.

Moisture Absorption

Moisture causes all kinds of problems for tiles that cannot resist water absorption, especially in an outdoor setting. As a result, the American National Standards Institute devised a means of testing tiles by boiling them in water, then comparing a tile's weight gain from its dry weight. For outdoor applications, particularly in areas with freezing and thawing cycles or with heavy precipitation amounts, the water absorption rating is even more telling than the tile's wear rating. Tiles ranked as nonvitreous or semivitreous have water absorption rates that are too high for outdoor applications. Vitreous tiles are suitable for outdoor use as they absorb moisture at rates between 0.5 percent and 3 percent. Impervious tiles are the best choice for outdoor use as they only absorb 0.5 percent or less water.

Coefficient of Friction

Tiles may be tough and moisture resistant, but if they have slippery surfaces they are likely not good candidates for use outside. A coefficient of friction rating provides information as to how much traction the tile provides. The coefficient of friction is a measurement of the force it takes to push an object across the tile surface, divided by the weight of that object. The higher the number, the more traction the tile provides. Coefficient of friction numbers are expressed as a figure between zero and one. Those tiles rated at 0.6 or better are excellent for commercial uses and they comply with the provisions of the Americans with Disabilities Act. They also serve well in outdoor applications.

Frost Resistance

A snowflake symbol stamped on the tile or on its packaging materials indicates the tile is frost resistant. Frost, and its accompanying freeze and thaw cycle, is enough to crack or otherwise damage tiles used outside. The presence of the snowflake symbol indicates these tiles can take the punishment of severe outdoor weather.