A.Tile consultant Michael Byrne responds: The most important factor to consider when choosing a tile for outdoor use is how often the tile will freeze, which depends upon the climate. In southern California or Florida, where an exterior tile installation might only freeze once in its lifetime, almost any tile will do. In a climate that has a frost once or twice a year, a vitreous tile should be fine. If your area gets a frost more than once or twice yearly, however, you need to use an impervious tile. Impervious tiles do not absorb any appreciable moisture that might expand when the tile freezes. Using substandard materials or methods can result in the loss of the tile after only one freeze/thaw cycle.
The tiles should be installed with latex-content thinset mortar and premium-quality latex grout. I recommend installing a sloping subsurface, a drainage layer to allow for runoff, and a crack isolation membrane to absorb differential movement between the tiles and the setting bed.
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