The several kinds of clay tile are made in much the same way. Thin sheets of clay are pressed or molded to shape, and fired in kilns in the same process as is used for making brick. The tile may be left in its rough state. It may also be given a smooth surface, called glazing, by dipping or spraying the tile with a material that joins with the clay. Other ways include throwing salt into the kiln or treating the clay with a chemical wash. Tile pipe is used for sewage-disposal systems and for draining fields of excess water. A continuous tile line is formed by fitting together short sections, each of which has one end enlarged to form a bell into which the small end of the next section fits. Drain tiles are laid with uncemented butt ends through which the drainage water may seep. Sewer pipes are laid with tight cement joints. Finer grades of clay are used in making tiles for roofs, for walls, and for floors. Roofing tiles are made in various shapes and colors. Hollow clay tile blocks are used in load-bearing walls and partitions. Home builders use decorative tiles for interior floors and walls.