7If extraordinary care be required, the pavement is covered with tiles two feet square, properly jointed, having small channels, of the size of an inch, cut on each edge. These are filled with lime tempered with oil, the edges being rubbed and pressed together. Thus the lime in the channels growing hard, suffers neither water nor any thing else to penetrate. After this preparation the upper layer is spread and beaten with sticks. Over this either large tesseræ or angle tiles are laid at the inclination above directed, and work so executed will not be easily injured.