Notebook, 1993-

MATERIALS & METHODS - Painting - Fresco

Limitations & Advantages - Painting Procedure - The Wall - Sketches, Cartoons, Transfer - Secco Painting - Brick Walls - New Walls - The Aggregates - The Lime - The Mortar - Making the Lime Putty - Mixing the Mortar - Intonaco - Brown Coat - Plastering the Wall - Rough Cast / Trullisatio - Sand Finish

Pigments - Brushes & Tools - Bianco Sangiovanni

Fresco - Plastering the Wall

The wall is covered with four different layers of mortar composition. Their combined thickness will usually be not less than one and one-half inches, and ancient Italian grounds have been as heavy as four inches. The heavier the wall, the longer it keeps its moisture, and the more time the painter has to work on it. Contemporary recipes for grounds are much like those described by the Roman architect Vitruvius [circa first century B.C.].

1. The first layer is called the rough cast, scratch coat, or trullisatio. It is usually made with a coarse aggregate.

2. The second coat is called the brown coat.

3. The third coat is called the sand finish.

4. The final coat, called the intonaco, is the coat on which the fresco painting is executed.

Thus the mortar goes from coarse to fine and from lean to fat, producing a wall of maximum strength in which the layers cohere most effectively. As the moisture begins to evaporate, each layer sets initially. After a longer period, usually about eight hours, the lime crust of calcium carbonate forms on its surface. A new application of mortar cannot hold well to a smooth layer of mortar on which a lime crust has formed. For this reason the layers of mortar will adhere to each other best if each coat of mortar is laid "wet-in-wet" on the previous layer before the lime crust forms on the wall. If this is impossible, the lower layer of mortar ought to be laid with a very rough surface so that it will afford a good mechanical grip to the new layer of mortar. In all cases the wall must be thoroughly moistened before a new layer of mortar is applied. One must wait until the wall, although moist, has no water standing on its surface, before troweling on the mortar.

[Kay, Reed. The Painters Guide to Studio Methods and Materials. Englewood Cliffs, NJ: Prentice-Hall, Inc., 1983. pp. 176-177]



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