>Okay, I have some tiles that students made that are going to be put
>onto metal posts, outdoors. I have the correct adhesive, but I want
>to know if I need to seal the tiles or just grout them? They will be
>in the weather, but can be covered up during the freezing temps.
It depends on the tile. High-fire tile is better outdoors in freezing climates because high-fire clay is less apt to absorb moisture. Low-fire tile absorbs moisture in the rain. High-fire is cone 6 to 10 (stoneware and porcelain). Low-fire is cone 010 to 04 (earthenware). If it has not had a chance to dry out after a rain before it freezes, the freezing can break or even pulverize the clay because water expands when it freezes. Using a waterproof sealer could help if it is totally dry prior to application of the sealer. The grout for any outdoor tile should be sealed after it has dried a few weeks. If they are low fire tile, perhaps the whole tile could be soaked in sealer and allowed to dry before installation.