10:30 Thursday 20th June 2019

The Structure and Properties of Historic and Modern Fibrous Plaster

Ornamental plasterwork is a common feature of historic buildings in the form of ceilings, cornices and a wide variety of mouldings. It is a natural composite material comprised of gypsum plaster reinforced with open weave hessian cloth (hessian scrim) and is termed fibrous plaster. Hessian (jute or hemp) has been used as a reinforcement for well over 100 years and partial substitution of glass fabric for hessian is a recent development used in modern structures which incorporate fibrous plaster. In December 2013 part of the fibrous plaster ceiling of the 112 year old Apollo Theatre in London collapsed during a performance. Subsequently Historic England initiated a wide-ranging investigation into the structure and properties of historic and modern fibrous plaster. The paper presents an evaluation of the microstructure of historic hessian fibre and gypsum plaster, sourced from buildings under renovation, and a comparison is made with virgin materials including hessian and glass fibres. Composite materials were manufactured by Hayles and Howe, Bristol in the form of flat rectangular plates containing different volume fractions of hessian or glass scrims. These composite materials have been tested in flexure and the results of these mechanical tests will be presented at EcoComp 2019.

The Structure and Properties of Historic and Modern Fibrous Plaster