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This month's restoration article looks at the pedigree of plaster and stucco and those involved in its development
The wonderful world of lime-rich render is part of our verbal archaeology, and every day we unwittingly relate to its origins. 'Plaster' might be defined as 'mouldable but usually level cementing material'. The Greek 'plastos', to mould or spread thin, comes from the same root as the Latin 'planus', spread flat. It evolved into 'emplastrum' a plaster (poultice, hence medical 'plaster'), which finally resulted in 'piastre', English and French medieval wall plaster. Modern 'plastic' has inherited the historic meaning of mutability.
Now 'stucco' seems a specific Italian word, probably coined with an inspired flourish during the Renaissance. But the Italians just applied a new meaning to another common stem. A dictionary of etymology will yield something like 'Stucco- n. external plaster (Italian). Compare with Old High German stukk/stucki: crust, piece, fragment. Also Middle English, stokki: made of wood.' Never mind our linguaphile ancestors, the German term is more prophetic as it anticipates that everything stucco will turn - if damp and exposed - into a fragmentary piece of crust.
It is remarkable how long plaster can take to get crusty in stable or dry conditions. Painted and delicately moulded lime plaster has survived for thousands of years around the Mediterranean. For the architectural busperson's holiday, one of the most remarkable and least-known survivals is at Ostia Antica (pictured above), ancient Rome's port, where a virtually complete bar/diner survives from the second century AD, its plaster complete with frescoes of food and still bearing the customers' toga rack. At the town's theatre, the soffits of the entrance tunnels bear traces of plaster in geometric relief patterns.
In about 30 BC, Vitruvius set out the basics of preparing the stuff to a formula which scarcely changed for almost 2,000 years:
' [Plasterwork] will be done properly if clods of first-rate lime are burned in the kiln, then, as it is softened over many days the remaining liquid, forced to boil away, will bake the clod to an even degree. If it has not been softened all the way through, but is used when only recently fired, then, when applied, it will develop blisters, because it has raw grains...