Devon Plaster Mouldings Specialists, F.H Crocker & Co examine the techniques used in early plasterwork.
The Origins of Fibrous Plaster
Fibrous plaster is rough and is composed of plaster laid upon a backing of canvas stretched on wood. It is typically used for moldings, circular and enriched casings to columns and girders and ornamental work, which, being worked in the shop and then nailed or otherwise fixed in position, saves the delay often attendant upon the working of ornament in position. Fibrous Plaster is the principal form used today for cornices and other fine decorative work and mouldings.
The various forms of plasterwork, from hand modelled stucco to glass reinforced gypsum may all contain some kind of fibre for strength, and most lime mortar ceiling work contains enough animal hair to bind the plaster together between the lath, contributing to its flexible strength and therefore its characteristic longevity. However, most lime plaster is run or spread in situ, and enrichments which may be added are usually small solid casts stuck to the background with a 'slip' of mortar, rather than cast in large sections. This is the type of work usually referred to in the trade as 'solid'.
The technique of reinforcing gypsum plaster with hessian or canvas has been known and used for thousands of years, and probably predates the Pharaohs. Millar, writing in 1897, mentions mummers' masks found in Kahun dating from 4,500 years ago.
The modern use of this material may be said to have started then, but the use of fibrous plaster was known and practiced by the Egyptians long before the Christian era; for ancient coffins and mummies still preserved prove that linen stiffened with plaster was used for decorating coffins and making masks.
Cennino Cennini, writing in 1437, says that fine linen soaked in glue and plaster and laid on wood was used for forming grounds for painting. Canvas and mortar were in general use in Great Britain up to the middle of the last century. This work is also much used for temporary work, such as exhibition buildings. However, modern fibrous plasterwork in England can be said to date from Leonard Alexander Desachy's patent of 1856, which drew on a Parisian recipe.
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Fibrous plaster has a number of key advantages over solid plaster and proved immediately popular. Fibrous plaster weighs much less and is better reinforced so plaster mouldings can be prepared in a studio or on site, prior to installation, avoiding the need to run mouldings in situ. The use of modular cast mouldings can allow great variety of ornament applied in a bespoke way. For example, incorporating a stock cherub into a dome made to specific dimensions saves having to model each cherub from scratch. The result was cheaper decoration and more of it. Fine plasterwork could now be afforded by more people, and those who could afford it could afford more of it.
Not only houses benefited, but also theatres, music halls and other settings where a grand effect was required with perhaps a limited budget and minimum take-up of space. Most theatres have accessways behind the facades and lighting rigs cut through ceilings, and in solid work their lavishly ornamented plasterwork would weigh so much as to require major structural support, decreasing the useful space behind.
Speed of operation on site is another advantage in a theatre. Normally, the decision making processes - the financing, the architectural and interior design, and the procurement take so long that the time left for execution of the project is cramped.
In the past hundred years, fibrous plaster has come into its own, as increasingly flexible moulding compounds have made it possible to produce casts with fine sharp relief, undercut decoration, piercing and inlays, and modern plasters have increased strength and lightness.
Conservation and Consolidation of Plaster Mouldings
Plaster mouldings are very fragile and become even more brittle with age, this can result in unsightly damage as definition is lost or whole sections destroyed. Good conservation practice requires that, wherever possible, surviving original work should be retained and repaired and, where necessary and appropriate, restored.
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With exterior mouldings
special consideration needs to be given to the renovation of exterior cornices, columns and corbels. Colour matching and material composition are additional areas requiring a wide range of skills and knowledge to ensure that an accurate and time tested solution is chosen. If the prevention approach has not worked or has been followed at all, then conservation of the plaster mouldings must take the form of consolidation. However, before any work is carried out, moulds must be taken of any area likely to be damaged in the preservation process, including any section showing rot, mould, water damage or vandalism for example.