We began by looking at the different categories of ceramic tiles which consist of Glazed Porcelain tiles (usually made from refined clays and glazed), Mosaic Tiles (usually of porcelain with color), Quarry Tiles (typically unglazed and made from common clays and shale), and Pavers (similar to quarry tiles but thicker and used in heavy wear areas, needs resealing once or twice a year). Tiles can then be glazed or left unglazed. Glazed tiles are nearly impervious to water and thus more resistant to mold, but the grout needs to be resealed as cracks form. Unglazed tiles require a sealant to keep clean and stain-free. There are sealants of different particle sizes which include penetrating sealants that soak into the tile itself and surface sealants that lay a thin coating on top of the ceramic and alter its appearance. One example of this tile sealer has a hazard statement saying it may cause eye damage, skin irritation, and damage fertility or an unborn child.