Although glazed ceramics do not need to be sealed against the outdoor elements, modified ceramics do. Glazes, while wonderful, are not easy to create and require access to a kiln. If you have other artwork that you have applied to your tile, such as paint or perhaps a child's drawing, you will need to weatherproof the tile by adding a sealant over the top. A good sealant will protect the tile and the artwork from moisture and the constant treading of feet.
Things You'll Need
Tiles with artwork
Select a sealant from your local craft or hardware store. There are many brands available, be it pond sealant, floor finish or furniture sealant, but there are a few key aspects that you will need to look for. First, avoid simple fixative as this does not form the hardy layer of material needed to protect your tile. Second, make sure that the sealant is watertight when it hardens, not merely water resistant. And finally, make sure that the sealant is non-yellowing. Some coatings will turn yellow over time when exposed to the UV rays of the sun.
Lay a layer of newspaper over your work surface. Don a mask and gloves. Many sealants have fumes that are unhealthy to breath, so protection is essential. Lay your tiles face up on the newspaper
Apply the artwork to your tiles if you haven't already. If you plan on having paper or other media on top of the tiles, paste them down so they remain flat. Make sure the tiles are clean of any debris.
Open the can of sealant and dip a broad paintbrush into it. Brush the sealant onto the tiles. Cover the artwork completely and paint to the edges of the tiles. However, avoid getting sealant on the sides of the tiles as this is where the grout will touch when you install your tiles. Brush the sealant in long, even strokes to create a consistent layer on your tile.
Wait for the sealant to harden. The amount of time this takes depends on the sealant you are using, but it will likely be a matter of hours to days. When it has hardened, spray a tile with several droplets of water. If the tile absorbs it, add another layer of sealant. Repeat until the tiles are watertight and ready to install.