Fibrous plaster explained

Fibrous plaster is a cast of plaster of Paris reinforced with hessian fabric and timber laths. It was patented in Britain in 1856 by a Frenchman, Léonard Alexandre Desachy. Panels and ornaments are made in a workshop, then carried to site and fixed up, rather than being modelled or run by hand on the ceiling itself.

It mattered because it was lighter, quicker and cheaper than traditional lime plasterwork, and it could take almost any shape. From about 1880 to 1910 it became the standard material for the lavish interiors of theatres and music halls, and it turned up in cinemas, banks, hotels, public halls and houses too.

How it is made

The plasterer starts with a mould taken from a model. A thin first coat of plaster of Paris goes into the mould to pick up the detail. Then comes the reinforcement:

• Hessian. Strips of coarse jute fabric, dipped in plaster and laid into the wet cast, give it tensile strength and stop cracks running through it.
• Timber laths. Thin lengths of wood bedded into the back stiffen larger panels and give the fixer something to screw or nail through.
• Backing coat. More plaster binds it all together. The result is a shell only a few centimetres thick.

Laths are left out of thin, narrow castings, because timber in a slender piece can make it warp. Once set, the cast is lifted from the mould, trimmed and taken to the building. Historic England notes that panels were usually limited to about two metres square, which kept them manageable on a scaffold.

Desachy, Jacksons and the 1858 openings

Desachy's first architectural work was at St James's Hall in London, designed by Owen Jones and opened in 1858. The Royal Italian Opera House at Covent Garden, opened the same year, was another early commission. It survives as the Royal Opera House, and Historic England records that it holds the oldest surviving fibrous plaster in the country.

The London firm George Jackson and Sons bought the patent in 1864. It expired in 1870, after which anyone could use the method, though Jacksons stayed the leading supplier for another decade.

Fibrous plaster made the gilded Victorian auditorium affordable: built in a workshop, hung in days.

Why theatres and Victorian ceilings used it

Lime plaster ornament was modelled or cast in heavy pieces and had to be fixed into wet work on site. Lime then needed time to harden before anyone could paint it. Fibrous plaster solved several problems at once:

• Weight. A thin reinforced shell weighs far less than solid plaster, which suited wide spans and deep coffered ceilings.
• Speed. Work was cast off site while the building went up, then fixed in a short time. It could be decorated almost straight away.
• Repetition. One mould could produce hundreds of identical boxes, cartouches and balcony fronts.
• Imitation. It could pass for carved stone, timber or costly hand-modelled work, which suited the theatrical taste of the period.

Good surviving examples include the Haymarket Theatre in London, remodelled by C. S. Peach in 1904, and Glasgow City Chambers. Look up next time you are in an old theatre: most of what you see overhead will be fibrous.

How it differs from solid run plaster

Traditional cornices were run in place. The plasterer fixed a timber rule to the wall and pushed a running mould, a sheet metal profile on a wooden frame, back and forth through layers of wet plaster until the full section was formed. The cornice is solid, built up in coats and bonded directly to the wall and ceiling. Enrichments such as egg and dart were cast separately and stuck into it.

Fibrous work is different in three ways. It is hollow rather than solid. It is made away from the building rather than on it. And it depends on mechanical fixings rather than on bond to the background. Fibrous lengths of cornice can be run on a bench using the same kind of profile, then cast and reinforced, which is why some Victorian cornices are run work and some are fibrous.

That fixing is the material's weak point. Fibrous ceilings below roofs were often hung from timber or iron by "wads" of hessian and plaster. If wads perish or are disturbed, a ceiling can fail. The partial collapse of the Apollo Theatre ceiling in London in December 2013 brought this into sharp focus, and Historic England published guidance on caring for fibrous plaster in 2019.

Living with it at home

If your house dates from the late Victorian or Edwardian period, some of its cornice or ceiling ornament may be fibrous. Tap gently: fibrous work can sound hollower than solid run plaster. Cracks along fixing lines, sagging or loose sections are a reason to call a specialist plasterer, not to reach for filler.

Our own pieces are hand-cast in plaster to order in Shrewsbury and arrive as natural plaster, ready for emulsion. For how decorative plaster developed before and after Desachy, read our short history of plaster, and for the terms used above, the cornice and mouldings glossary. To see Victorian-style roses, browse our heritage and classical collection.