Grade 1 provides resistance to severe frost action.The standard provides a classification by grade for durability and a classification by type for appearance.Ī roof tile’s resistance to freeze damage is classified as one of three grades: These photos show the long-term results of incomplete vitrification, resulting in moisture absorption and freeze damage.ĪSTM International (formerly, the Association for Testing and Materials) provides the following standard for clay tiles.ĪSTM C1167, “Standard Specification for Clay Roof Tiles,” addresses material characteristics, performance requirements, and dimensional tolerances for roof tiles. Tile density is determined by the fineness and purity of the clay, and the duration and temperature of the firing process. The density of the tile is an indication of its quality high-quality tiles are more dense than low-quality tiles. This is just background information you are not required to confirm compliance with standards. You won’t know whether tiles comply with any standards unless documentation is provided. Glazing is sometimes applied to the top surface of tiles for decorative effect and to help reduce moisture adsorption.īoth clay and concrete tile installed in areas subject to freezing temperatures should comply with ASTM manufacturing standards designed to prevent freeze damage. Low-quality tiles are more porous and more vulnerable to freeze damage. When moisture in tiles freezes, it expands, causing delamination and surface deterioration or spalling.
Incomplete vitrification will result in the finished tiles being more porous, which means they’ll absorb moisture more easily. For clay tile, the vitrification process is key to long-term durability.
#GLAZED TILE ROOFS FULL#
Full vitrification turns clay into a glass-like material. Vitrification happens when the various minerals in clay change and bond chemically to form a single, dense, non-porous tile. Molds are filled with a fine, wet clay, and then baked in a kiln until vitrification takes place. They’re manufactured using a casting process. Clay tiles are another roofing material that has been used for a long time.
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