How Ot Maintain Plaster Molding National Parks Service

Walls & Ceilings

How To: Rebuild a Wall with Three-Coat Plaster

A true, traditional three-coat plastering chore is the longest-lasting and most faithful manner to consummate a wall in a flow home. At in one case both an art and a science, this type of plastering is a refined skill that master tradesmen spend years developing and perfecting.

Three Coat Plastering - Tools

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On the Manhattan Brownstone project, Bob, Chris Vila, and architect Brian O'Keefe discovered an intact ceiling cornice that made them rethink plans to completely gut the interior infinite during demolition. Instead, they decided to proceed the cornice and make it a focal point for the large living area in the center of the floor-through flat.

Facing the challenge of rebuilding the wall without changing the profile or having drywall that extended beyond the face of the cornice, the team turned to Boro Plastering of Hyde Park, N.Y., to create an original plaster wall that would dovetail with the existing cornice.

The Manhattan remodel is not a strict restoration projection, simply the craftsmen involved recognize the value of loftier-quality workmanship as evidenced in the original construction. A true plaster job is the best way to complete a wall in a menses home. There'south no doubt that "three-coat plaster is unmatched in strength and durability," according to the National Parks Service. "It resists burn down and reduces sound manual." It also most closely replicates the original finishes in this Upper Due west Side Brownstone.

Three Coat Plastering - Lath

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Nuts of Plaster and Lath

When plastering walls, plaster must exist practical in such a way that it adheres to the support wall surface, bears its weight load without cracking, and exhibits a smoothen, difficult, finished surface suitable for painting or papering.

A quality plaster task begins with the lath on which the plaster volition be applied.

Traditional lath and plaster jobs used wood board, but the moisture level in wood makes it aggrandize and contract, which can make plaster crack.
Metallic lath is a more than reliable surface for plastering since it does not retain moisture and provides more "keys" or spaces in its surface for proper adhesion.

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Three-Coat Plaster System

The three-glaze plaster system begins with two coarse or crude coats. These coats form the base of the wall and are mixed of lime or gypsum, aggregate, fiber, and water.

The lime is typically derived from limestone or ground oyster shells. Many firms now piece of work with gypsum since information technology eliminates the demand for added fiber and has a much quicker set up and drying time. Boro Plastering works with a ratio of three-to-ane, bags of sand to bags of gypsum, for their rough coats.

Scratch glaze: The showtime coat is chosen the "scratch coat" and is applied at 3/8 inch thick then scratched or scored with a comb to give it a rough texture.
Brown coat: The second rough coat is made of the same mixture and is called the "brown coat." The dark-brown glaze is applied directly to the scratch coat, also at a 3/8-inch thickness, merely left unscored. The sand provides a rough texture that gives the light, 1/8-inch finish glaze a surface to grip onto.
Terminate glaze: The third and last coat is an application of lime putty, which gives plaster walls their polish, hard, shiny finish.

Three Coat Plastering - Finish Coat

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Information technology'southward All in the Mix

With a traditional lime finish coat, the plasterer becomes a chemist. "This is where fine art meets science," Bob says, equally he watches the mix being prepared for the lime putty.

This lime putty is used for the finish coat of plaster that is skimmed onto the wall and smoothed to create a hard, shiny terminate coat. To create the lime putty:

First the plasterer creates a "gauge" that is a circle of putty, banked up like a swimming pool, on the mixing board.
Into this circle he pours water, so sprinkles the water with plaster. The measurements are inexact to the untrained eye, but very precise to the plasterer who has to "feel it out," as Gary Annino of Boro Plastering explains.
Once poured in, the lime and plaster mix is left to "slake" or sit and transform itself.
The reaction is complete when the slaked lime stops giving off rut. At this point it is gear up to exist mixed into putty.

Master plasterers work with a spray canteen to keep the plaster wet every bit they shine it to a perfect end.

Three Coat Plastering - Brick

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Below the Surface

"Each plaster task is unique," Annino says. The quality of any plaster chore and the degree of adhesion depends, in large office, on the integrity of the surface on which it's applied.

The plaster crew must starting time appraise the existing walls, masonry, or ceilings that need to be plastered. "Our crew makes a conclusion on an individual basis," Annino says. Sometimes they can use the brick surface that remains, sometimes they must affix wire lath to the brick to serve as a back up for keying the new plaster.

In the Manhattan Brownstone project, a variety of methods were employed, including plastering directly over the existing brick walls that were get-go treated with a blue bonding agent. In areas where the brick had deteriorated, wire lath was used to create a sound surface and a level wall. Where the ceiling had been punched open up for ceiling supports, patching was done with wire mesh and plaster earlier a skim glaze was applied to the entire ceiling. The crew crafted the job around the cornices, building plaster walls and reviving the ceiling without building out beyond the cornice profile.

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