Saturday, February 1, 2014

Plaster Word of the Day; 31 - 40

Image courtesy of Palladio Mouldings

Pre-cast plaster mouldings really did not become widespread until the late 19th century. The innovations in gelatins and incorporation of jute cloth and wood reinforcement became known as ‘fibrous plaster’ in England and ‘staff’ in France.

Staff sounds particularly un-French. Urban legend has it that they originally used sticks, ‘staffs’ to hold up the mouldings until they set. I tend not to believe that the French adopted an English word even if that ever was their practice. More likely it derives from old French ‘estofer’ meaning to enrich or decorate.


Image courtesy of Plâtres Vieujot
Today associated with the natural building movement, the 19th century American innovation of utilizing straw bales as a building member provided affordable, highly insulated dwellings that comfortably withstood the harsh winters of the Mid-West prairies.

Straw is an ideal substrate for traditional plasters made from mineral binders such as clay, gypsum and lime.


An acronym for Glass Fiber Reinforced Gypsum. Sometimes described as GRG or GFRC if cement is used instead of gypsum. Layered fiberglass between brushed or sprayed on coats can provide a significant increase in tensile strength. Pieces can be cast much lighter, as thin as 3/16”. Often this is a good specification for large ceiling mouldings such as vaults, domes, coves and arches.

Image courtesy of Palladio Mouldings


Fiberglass is available as a spool of linear thread that can be chopped up with a gun and mixed directly into the plaster. Also available in bulk pre-trimmed to specified lengths.


A finely woven fiberglass cloth that is very thin and flexible, allowing for multiple coats


A coarsely woven fiberglass fabric that is more rigid, usually applied in one or two coats only. An alkali resistant version is commonly used with GFRC work.

Image courtesy of Plâtres Vieujot

‘Harling’ is an external render technique common to the UK and Northern France to finish a masonry substrate. After an initial coat of stucco is applied and whilst still wet, a variety of materials such as pebbles, gravel, sand or shells are added to a slurry of the same material and thrown against the surface using a shovel like tool called a ‘harling trowel’.


A similar technique where just the aggregates are ‘dashed’ or thrown against the wet stucco surface.  

Contributed by Patrick Webb

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