From its origin as a British colony the United States inherited a fully developed plaster tradition that would
expand considerably from the
century until the 1940s. The fine craftsmanship can still be enjoyed
in public settings such as period railway stations, banks,
courthouses and capitals across the nation. Many fine plaster
ceilings enduringly grace private residences in historic
neighborhoods such as Brooklyn Heights and Peninsular Charleston.
|East Room, White House
However, in the decades following World War II plaster ceased being specified and plastering rapidly diminished as a trade. What happened? Two distinct movements figured prominently: the ascendency of architectural Modernism and cheap, industrialized residential construction.
|Pre-fabricated home. Levittown, PA
Modernist architectural programs were no longer teaching the traditional language of ornament. By contrast, students were learning that ornament was born of a superstitious and deceitful past, craft was a criminal enterprise injurious to the human spirit and that industry and technology were to be embraced as the basis for a new, purer aesthetic. At the same time, prefabricated temporary housing developed for the military during the war was being modified by developers for residential use. Factory produced construction systems were designed to be assembled by unskilled, replaceable laborers. Part of the package was to replace traditional plastering with nascent “dry” wall systems. By the 1980s there were practically no traditional plaster apprenticeship programs, little opportunity for training, by all appearances the trade had died.
|Grand Central Station, NYC|
Gypsum drywall has largely displaced traditional plastering for interior walls and ceilings. Many homeowners are surprised to discover that the vast majority of the gypsum used for drywall is the waste byproduct of coal-fired power plants pollution control systems. This is in contrast to gypsum, lime and other plaster binder materials that are mined from naturally occurring deposits. I would like to highlight a few specifications where traditional plasters should be considered as a practical alternative to drywall:
- Monolithic substrates
- Curvilinear surfaces
- High durability
|Plaster applied directly to
|Running a barrel vault in place
courtesy of Sloan Houser
Curvilinear surfaces which may include walls but are often horizontal ceiling surface such as domes, vaultsand the underside of staircases are a logical consideration for plaster specification. I've been on many projects where vaults are painstakingly framed out with what is commonly called “ship hull framing” to receive multiple layers of ¼” drywall that has to be cut into small strips, soaked and scored in the back to adjust to the curvature. This is completely unnecessary and an inferior construction to traditional plaster over lath, requiring only nominal framing.
|Courtesy of Louvre Museum|
and Plâtres Vieujot
Cast Mouldings and Ornament
As the millwork industry became increasingly sophisticated, soft “paint grade” woods such as pine and poplar began to displace plaster as the economic plain moulding specification. The integration of ornament enrichment into mouldings slowed this transition until ornament itself was largely stripped from architectural design in the mid-20th century. Nevertheless, there are many strong arguments for specifying plaster mouldings with the following specifications often being competitive or less expensive.
- Medium to large curvilinear profiles
- Non-radial curvilinear profiles
- Large, complex crown mouldings
- Curvilinear oriented mouldings
- Low maintenance
|Image courtesy of|
Straight mouldings can be produced just fine in plaster but it excels like no other medium in being able to contour to curvilinear shapes. I say curvilinear as opposed to radial because plaster is not constrained physically or economically to arcs of circles but can readily accommodate ellipses, hyperbolae, or free formed curves. The process helps to explain this property. The first step in creating a plaster moulding is hand-cutting a reverse metal profile from a template. The profile is mounted on a jig and the plaster is built up in successive layers on a table or ramp. For plaster it matters very little if the profile is large or small, very complex or composed of non-radial curvilinear elements. In fact, the moulding itself can be curvilinear such as vertically for architraves surrounding arches, or horizontally as for moulding applied against a curvilinear surface or even complex helix shapes as sometimes encountered in the stringers of descending staircases.
|Students learn to sculpt, cast and apply|
plaster ornament at the
American College of the Building Arts
Particularly when large or ornate mouldings are specified I have found clients concerned about maintenance becoming an issue. The coefficient of expansion of soft woods is relatively high with changes of temperature and especially humidity. This is exacerbated by the reality that wood mouldings are typically affixed mechanically against drywall or plaster materials that have a very low coefficient of expansion. The wood moulding moves, the wall does not and cracks develop quickly between the disparate materials that are either addressed with caulk or lived with. Alternatively, plaster mouldings are affixed with plaster to a plaster (or drywall) substrate. The result is a monolithic system, the bond is so strong that the mouldings literally become a part of the wall. Most plasterers will guarantee that aside from structural movement their work will not crack, ever.
This article is a brief summary of a subject that can become very specific for a given project. As a technical consultant for plaster materials and application, I provide services to architects helping them properly specify plaster and plaster systems. I also work with plaster contractors providing training and onsite consultation services as needed.
Contributed by Patrick Webb