Fresco - Rough Cast / Trullisatio

1. The mortar should be fairly stiff, clinging to a tilted trowel.

2. The mortar is thrown from a throwing trowel held about a foot and a half from the wall. The masons throw it with a sidewise motion--that is, diagonally from [p. 177] their left to their right, so as not to spatter back in their faces and so that bubbles will not be caught too easily in the application.

3. The mortar is leveled with a straight-edge plank and then scratched evenly and deeply in all directions with a metal scratching comb to make a grooved rough surface to which subsequent coats will cling well.

4. The wall is sprayed with water before it sets.

If unglazed pottery, red tile, or bricks are crushed to the size of small peas and substituted for 30 percent of the sand in this coat, it will increase the water retention and toughness of the ground as well as its roughness of surface. In this case the scratch-combing of the surface may be omitted.

When lath supports are used, goat's hair or fibers are sometimes added in small amounts to keep the mortar that has been squeezed through the lath from dropping off while it is still wet. Such fibers should be soaked in the lime putty for a day or longer to rid them of oils and impurities.