Period character guide: Decorative plasterwork

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Decorative plasterwork has fascinated me ever since I lay in bed as a child in some ancient house we were staying at, staring up at the ceiling and marvelling at the play of light and shadow across the folds and swirls created by craftsmen. The room must once have had considerable status as these ornamental elements were designed to impress visitors while the more workaday areas of a house lacked any embellishment.

Stucco – a plaster mix of lime, gypsum and marble dust perfect for fine work – was developed by the ancient Romans to decorate ceilings, and was widely used in Europe. Influenced by the Italian Renaissance and the subsequent fashion for Baroque style, decorative plasterwork was employed to spectacular effect on the ceilings of some of Britain’s grandest houses.

The mid-17th century, barrelvaulted plaster ceiling in the long gallery at Lanhydrock, Cornwall, owned by the National Trust, is just one early masterpiece. But it was the Georgians in the 18th century, led by the Scottish neo-classical architects, the brothers Robert and John Adam, who spotted the true potential of decorative plasterwork. Elaborate egg and dart designs, stylised foliage such as acanthus leaves and flower motifs are all contained in the period’s pattern books. A fine example of the time is Fairfax House in York, built in 1762, where ceilings and walls are covered in supremely wellexecuted stucco decoration.

Cornices serve a practical purpose as an architectural device to cover structural joints between the walls and ceiling, and along with ceiling centres, friezes, corbels, panels, dado rails and skirtings, plaster mouldings became an art form during this era.

Cornices were put up in situ using a ‘running mould’ and plaster ‘enrichments’ (individual decorations) were added to enhance the overall effect. The process was revolutionised in 1856 when a Frenchman named Desachy patented fibrous plaster, a lime-free mix that incorporated flimsy sheets of hessian to add strength. Much lighter than solid plaster, fibrous plaster makes it possible to cast complete lengths of cornice and various other items together in one prefabricated piece.

When fibrous plaster was combined with the use of the flexible gelatine moulds, first shown at the Great Exhibition of 1851, a vast array of decorative details could be mass produced and decorative plasterwork began to be seen in more humble homes of the Victorian period, with its use continuing well into the 1930s.

ABOVE (clockwise from top left): This wood and metal running mould has the shape of the cornice and is used to take the measurement of the moulding that’s being copied; dating back to Victorian times, original moulds include popular patterns such as egg and dart, gothic arches, Greek key, dental edging and modillion blocks; the rather messy job of brushing the gypsum on the rubber mould; a new rubber mould for the popular egg and dart pattern for cornicing; a Butcher Plasterworks craftsman at work using a running mould to create a plaster mould for a run of cornicing.

Plasterwork today
Fibrous plaster cornice of almost any design can still be ordered by the length and you can have enrichments cast to replace missing or partially broken sections. However, producing decorative plasterwork is an understandably messy business and, although I escaped unscathed from my visit to Butcher Plasterworks in north west London, there is hardly a space in the workshop untouched by plaster residue.

The Butcher team are highly skilled, mixing the plaster and brushing it into the moulds with the panache of celebrity chefs. Assistant manager Warren Ringer explained that fibrous plasterwork consists of plaster, hessian sheets and timber laths which both strengthen the work and provide fixing points to enable the finished piece to be screwed into place. The moulds used now are no longer gelatine but a flexible rubber compound.

Casting a cornice takes about 20 minutes. Plaster is poured and brushed onto the mould and hessian scrim is laid onto it, more plaster is added and then the thin timber laths are laid along the length. The hessian is then folded over so it forms a double layer, holding the laths in place. Once a final thicker layer of plaster has been spread and the excess ‘struck off’, the cornice is allowed to dry completely before then being lifted out of the mould.

In many ways this is the easy part. As Warren points out, making a mould to reproduce an original cornice involves painstaking work. He showed me enrichments taken from a 100- year-old cornice and explained that six layers of paint had to be removed to reveal their detail and true beauty. ‘Squeezes’ will be taken from these so that eventually a 3m long ‘master model’ can be carefully built up on the bench in the workshop. From this a rubber mould is made to enable new lengths of the cornice to be cast.

Simpler moulds are made of plaster coated with shellac varnish. Warren says that over the years Butcher Plasterworks has built up a collection of stock moulds from all periods and that new designs can be created by a process of clay modelling in much the same way as craftsmen would have done generations ago.

Care and repair
Decorative plaster can easily become a casualty of renovation work. In a Victorian house I was renovating part of the ceiling came down, bringing a section of cornice with it. Quick thinking saved the day when the builder suggested I cut round the edge of the rest of the collapsing ceiling with a sharp knife to separate it from the cornice. It was tedious work but, with some minor repair, the cornice survived and the ceiling was replastered up to it.

Where the ceiling itself is decorated, and is losing its bond to the structure above, there are several methods of reattaching it but it is best to call in a specialist. In the meantime, prop it from below with padded boards and poles.

Small sections of decorative plasterwork can be run in situ, but the work requires skill and larger sections will need to be made up by specialists. A large range of fibrous plasterwork is available off the shelf, but take care to ensure items are appropriate to the scale, period and status of your home – decorative plasterwork reflects distinct period styles.

In any repair work it is worth remembering that what looks like plaster may be wood or papier mâché and that sometimes these materials were combined. Each material will require different repair techniques.

Often, the true beauty of old mouldings is lost because, over the years, they have become clogged by the application of successive layers of paint. The underlying layers may hold a unique record of the original paint colour so you should consult the local authority conservation officer before stripping this if your home is listed or particularly old.

Warm water, steam, chemical removers, poultice systems and proprietary wallpaper stripper may all be successful in removing paint from plaster but always undertake a test first on a small unobtrusive area and take care to avoid accidental digging with scrapers. A toothbrush and a sharpened stick are helpful in picking paint out of deeper recesses. Never use abrasive methods such as wire brushes or sanders.

Making fibrous plasterwork

1 A good even layer of plaster and water mixture must be applied to the rubber mould with a brush.
2 Casting a length of cornice.
3 Hessian strips are applied within the cast to strengthen the cornice cast.
4 Brushing in plaster into the dry hessian to further strengthen the cast. Fibrous plaster sets harder and faster than plaster used for walls.
5 A floral Victorian cornice is inspected for flaws before being transported to the site. Plaster mouldings can be fabricated in the workshop and quickly installed.
6 A fleurs-de-lys cornice is commonly found in Regency properties.

Word for word: A decorative plasterwork glossary
Enrichments: decorative applied mouldings that are individually cast.
Master model: an exact full size model of a cornice, frieze or other decorative element from which a mould is taken to enable new work to be produced.
Running mould: a zinc template fitted to a wooden stock which is run through wet plaster to create a cornice and other profiles.
Squeeze: a casting taken so that a moulding can be reproduced.

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WORDS ROGER HUNT PHOTOGRAPHS ROGER HUNT; ANDREW MONTGOMERY COURTESY OF BUTCHER PLASTERWORKS; LANHYDROCK NTPL/ANDREAS VON EINSIEDEL
Featured in the January 2009 issue of Period Living