After week 1 most of the arriccio was not on the wall yet and we had to take some down as well because it was too shallow. We trucked on regardless. Onto the brown coat, which is also know as the sand coat. It is also laid down under the intonaco no matter how many layers of arriccio are placed down.
The process goes as follows: Wet the arriccio (if dry) with a spray bottle. A slip that is a brushing or wash of lime water or diluted sand coat is sometimes used. The ratio to fine sand and lime is 2:1. The sand coat is applied (smeared) with a round-nosed trowel and leveled with a wooden float. The float serves to shave the sand coat and make it level.The float is moved in a circular pattern. The wooden float is preferred for the sand coat, while a stainless steel “aermicano” or rectangular trowel is preferred for the intonaco. The steel trowel served to polish the intonaco.
These photos include all three layers; the arriccio, sand coat, and intonaco.
Next, you need to mix the intonaco mixture, which is a 1:1 mixture of marble dust and lime. It should be placed ~20minutes after the sand coat, while it is still fresh, but not so that it may be moved by touch. This will prolong painting time and assure a strong bond. The sand coat can set one to 12 hours, depending on the conditions. You should only set the amount that you can do for a giornata (day’s work). We use two tests to ensure the sand coast is ready: the thumb print test, and the “kiss” test. The intonaco is applied (Spread) with the trowel in arc-shaped strokes. It should be worked with the stainless trowel in the same direction, as it sets, to create a perfectly smooth surface. Intonaco preparation is divided into three steps, allowing time between each. First, the intonaco is applied and patched, second it is smoothed, and third, it is polished, or burnished. As particles of marble dust are faceted, compression and smoothing will turn a flat side of the particles to form the intonaco surface. This surface should appear glossy. The intonaco should set an hour of more before painting, depending on conditions. Painting time generally lasts 12 to 24 hours. Conditions for drying will depend on atmospheric humidity and type of support (wall) being used.
There was a quick sketch laid out with a sinopia on the arriccio. Then the class went crazy, turned on some Taylor Swift, and went with it. And yes, a dance party did commence.