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Fibrous Ceiling Plaster
Transcript of Fibrous Ceiling Plaster
Historic Plaster Conservation Services Limited
Reading Room, British Museum, 1857
Actually, papier-mâché but a strong precursor in form to the fibrous plaster ceilings that followed over the next 70 years.
Fibrous Plaster Ceilings
Presentation to Wiss, Janney, Elstner Associates Inc.
New York, March 31, 2015
Since the Mid 19th C.
Building Construction has become more INDUSTRIALIZED
Affordability became a problem
All made in situ
Alterations to the mechanical systems in the plenum space above these ceilings is a typical source of impact damage that punctures and or fractures panels
Careless footfalls as maintenance is being done are very common. Trades do not usually realize how fragile the panels are
Most fibrous plaster ceilings in Seismic Zones will need to be reinforced or replaced as new tougher building codes are put in place.
As an example, Ottawa, Canada’s national capitol lies on a fault line. As they come up for renovation and renewal, all the government buildings in the Parliamentary Precinct are being seismically reinforced.
Number one cause of problems is water infiltration from roof leaks or leaking mechanical systems
The plaster is not even slightly water resistant. The fibers are subject to rot and desiccation
Continued water exposure in cycles of wet and dry destroys these ceilings
Pattern Maker, a brand new trade is the highest skilled job in the process
A pattern is created and from it a mold is produced
Molders tried to make designs that would “draw” from one piece rigid molds with no undercuts
Painting techniques were used on the finished plaster to enhance the three dimensionality and visual interest
Loose plaster is brushed into the mold which has been waxed or otherwise treated with a release agent
Fibers are collectively referred to as TOW
Tow is extracted from Flax, Jute and Hemp and used loose as a chopped material
When Tow is woven into fabric it is called Hessian, similar to burlap
Later sisal is made from Mexican agave cactus
All plant fibers
The finished thickness of a cast plaster panel like this might only be ½”
Sometimes a metal or wood armature is attached to the plaster panel at the factory with loose strands of Tow soaked in wet plaster and formed as a wrap over the armature
Panels were hung in place and USUALLY tied to framing with twine
Plaster wads were formed over the connection points and to connect panels together
Surface defects are repaired
Decorative finishes are applied
Buildings within the Parliamentary Precinct in Ottawa that have significant
Fibrous Plaster Ceilings
Sometimes a wood or light metal frame was attached to the panel at the factory with wads of plaster. In these cases wires were usually used to tie the panels to the building frame.
There is, in our experience, an incorrect assumption that Fibrous Plaster panels were made with an internal armature of wires or other substantial non-plant fiber material from which they were ultimately safely suspended.
Former Ottawa Railroad Station now a Conference Facility
Mass Produced Elaboration
I have never found an internal armature of metal inside an otherwise fibrous plaster ceiling panel.
Fibrous Plaster manufactured in thin lightweight panels allowed a pared down degree of elaboration without the cost and skill of traditional plaster.
"Bell Epoch Grandeur" Enabled
This pattern requires:
One square panel
One elongated pentagon
Cover Trim cut to length
Making a Fibrous Plaster Ceiling in 4 Steps
Patterns and Models are Produced
Plaster is Brushed into the Mold
Tow or Hessian is Embedded
More Plaster is Brushed into Mold
Installation on Site
What Goes Wrong?
Look for the Armature
There may or may not be an armature, and if there is it may only be attached to the panel with wads of fiber
Typical High End Fibrous Plaster Ceiling
Attic View of Same Ceiling
Sir John A Macdonald Bldg. Ottawa
Currently undergoing rehabilitation
…..a complex combination of Fibrous Plaster and Plaster on Expanded Metal Lath
Without pointing fingers………
Investigation Required Cutting a Cross Section Through The Wads
Today we would describe this as unsustainable!
Only Moderate skill required
Safety - The product is non-combustible
What holds it up?
2 Treatment Options
Hand lay up a repair using polyester fibers in an acrylic gel format.
Spray apply a pre-mixed product specifically made for repairing this kind of plaster.
Get consistent quality of application over large areas
LARGE SCALE SEISMIC or Whole Ceiling REPAIR
After thorough cleaning and primer application
A new mat of acrylic gel containing Aramid Fibers is sprayed over the entire surface
This reinforces the individual panels where damaged, and reconnects the panels to the metal frame to which they were once attached with wads of plaster soaked fiber.
A continuous well bonded covering of Kevlar™ reinforced acrylic makes the connection between the plaster and the structure safe and sound.
HPCS Aramid Gel is reinforced with DuPont® Kevlar™
The Art of the Plasterer, available from Donhead Publishers
Hand Layup recipe is classic Morgan Phillips thixotropic acrylic gel. See: APT Bulletin Vol. XII No. 2, 1980
All subject to rotting and desiccation
Here are two examples
Wads of plant fiber covered in plaster!