How To: Rebuild a Wall with Three-Coat Plaster

It’s All in the Mix

With a traditional lime finish coat like the one used in the Manhattan Brownstone, the plasterer becomes a chemist. “This is where art meets science,” Bob says, as he watches the mix being prepared for 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, and then 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 heat. At this point it is ready to be mixed into 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 finish coat. Master plasterers work with a spray bottle to keep the plaster wet as they smooth it to a perfect finish.

Beneath the Surface 

“Each plaster job is unique,” Annino says. The quality of any plaster job and the degree of adhesion depends, in large part, on the integrity of the surface on which it’s applied. The plaster crew must first assess the existing walls, masonry, or ceilings that need to be plastered. “Our crew makes a determination 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 support 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 first 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 for ceiling supports, patching was done with wire mesh and plaster before a skim coat 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.