Fresco - Making the Lime Putty

The quick lime is carefully combined with water in a wooden trough until a fairly liquid consistency of slaked lime is attained, a long-handled hoe being used to mix them together. Considerable heat is given off, and care should be taken to avoid burns while mixing the lime with water. After it has cooled, the slaked lime is shoveled into a steel drum or a storage pit so that it may age as long as possible, several years when practical. The structural quality of lime putty improves continuously with age, and aging is a further guarantee that there are no unslaked clumps of quick lime left in the mixture, which could cause trouble later. Aged lime putty may be bought from suppliers of construction [p. 173] materials, but further aging in a pit will improve it. When the lime putty is stored, it must be covered. Storage pits should be dug in the earth well below the frost line since freezing would ruin the putty. The pit should be lined with sand and gravel, and the storage box and cover, constructed of tongue-and-groove wooden boards, is put down into it. After the lime putty is shoveled from the trough into the storage box, water is poured over the mixture and left standing to prevent its drying, the cover is put on, and earth is shoveled back over it. In the past European masons are said to have used lime over twenty-five years old, each generation of mason putting down a new batch of slaked lime, so that succeeding generations would have a replenished supply of well-aged lime putty.

[Kay, Reed. The Painters Guide to Studio Methods and Materials. Englewood Cliffs, NJ: Prentice-Hall, Inc., 1983. pp. 173-174]

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