In 2013, we addressed the peeling plaster in the Denison Homestead’s front stairwell area. We brought in Marshall Plastering to restore the old plaster while maintaining its historic appearance.

Marshall Plastering is a seventh generation plastering contractor that specializes in historic plaster restoration, repair, and reproduction as well as, new construction projects. 

Owner and Denison descendant, John Marshall is acknowledged as one of the top plasterers in Connecticut and is an expert at determining the proper materials and techniques for each job. Over the last 45 years, Marshall Plastering has completed projects throughout New England and New York that include National Historic Landmarks, historic organizations, museums, churches, libraries, theaters, and private residences.

“We were pleased with John’s exceptional work on the stairwell project seven years ago and  asked him back to restore the peeling plaster ceiling in the Federal Parlor later this year,” said Julie Soto, Homestead Manager

The stairwell project gave us an opportunity to learn more about the construction of Pequotsepos Manor, look at the original plaster up close, and learn how labor intensive the process is to use and restore plaster.  

It took several weeks to scrape layers of paint and loose plaster from the walls and ceiling of the stairwell from the first-floor landing to the attic. 

John Marshall stopped by the Homestead to check out the integrity of Federal Parlor’s plaster ceiling to see if it needed to be stabilized in preparation for work being done on the beams above the room. There was only a small patch of loose plaster which was removed. We were told the material was original to the house - making it about 300-year-old plaster. 

The picture shows the back of a fragment of that plaster and the impressions left by the lathes. If you look closely you can even see tiny hairs. This is “horsehair plaster”. Yes, it really has hair in it - though maybe not from a horse.

Plaster has been used as an interior and exterior wall covering for thousands of years. It consists of a binding agent (clay, lime, gypsum, or cement), an aggregate (traditionally sand), and water; fibers such as hair are often added for strength.

Plaster was rare in the very oldest New England houses. Walls were finished with wood wainscoting. As the colonists became more established, building methods became more sophisticated.

In 1641, a general court in New Haven laid down day rates for lime plasterers, indicating that someone was doing the labor and needed to be paid for it. It was not yet common.

J. Frederick Kelly, the architectural historian who wrote Early Domestic Architecture of Connecticut and consulted on the restoration of the Homestead in 1946, thought plaster was introduced later to the Hartford area, and only became widespread after 1735.

In the restoration of the Homestead, Kelly chose wood wainscoting for the Colonial Kitchen. This room is the oldest original room dating back to 1717.  

The next room chronologically, the Revolutionary Bedchamber, and all the later rooms have plaster. It is possible that the lower floor front rooms—the public rooms, in our case the Federal Parlor and Annie’s Parlor—got plaster first while the upstairs rooms and the back kitchen had wainscoting and were plastered later.

It was also common in 18th and 19th century New England houses for the fireplace walls to have fancy wood paneling and the other walls to have plaster, as is the case in our Federal Parlor and Victorian Bedchamber.

In some New England areas, lime was hard to obtain, Clay was used to plaster early houses. However, along Long Island Sound, lime-containing seashells were abundant. Sometimes the colonists used shells from giant midden piles left by the original Native American occupants of the land (there was one near State Street in New Haven).

In some cases, these mounds might have been hundreds or thousands of years old! The shells, which like limestone, were mainly calcium carbonate, were ground up and heated in a kiln to produce calcium oxide (quicklime). Then the quicklime was “slaked” (mixed with water) to form calcium hydroxide, and then mixed with sand and hair to make the plaster. Over time, on the wall, the calcium hydroxide in the plaster would react with carbon dioxide in the air, losing water and changing back into the original, hard calcium carbonate.

From examining old walls in Connecticut homes, Kelly thought that the oldest plaster walls were usually made with only one coat. They used “accordion” lathes; that is, the lathes were made by sawing a piece of oak 3/8 or ½ of an inch thick, then splitting it on alternate sides.

The lathe, in one piece, was stretched out and nailed to the studs. This minimized the number of nails needed, a necessity because nails were handmade and expensive. The lime was roughly ground—Kelly says he often found large pieces of oyster shell in walls—and the plaster was mixed to be heavy on lime and extraordinarily strong. He says that the most common fiber he saw was red cow hair, a useful detail for anyone who ever wondered what the colonists’ cows looked like. These walls were clearly durable, at least in some cases—Kelly found some in good condition in the 1920s—but somewhat rough in appearance.

Later, plastering techniques became more refined. In the late 18th and the 19th centuries, plaster walls and ceilings usually had three coats. They were still made on a lathe backing, but the lathe boards were separately split or sawn and nailed to studs with cheaper manufactured nails, 3/8 to ½ inch apart.

The first coat of plaster was the scratch coat; it was pressed between the lathes to form “keys” which held the plaster to the wall, about 3/8 of an inch thick over the lathes. The scratch coat was “scratched” with a tool to let the next coat attach to it, and then left to dry. The second coat, the “brown coat” was also about 3/8-inch-thick; it was very carefully applied to make the surface of the wall or ceiling flat and even. The last or “finishing” coat was thinner, about 1/8 inch. It was usually made without hair and with more lime and less sand, to be perfectly smooth. Sometimes special additives were mixed in, like gypsum for fast drying or marble dust for a hard, polishable finish.

“Horsehair” plaster rarely contained actual horsehair. The long hair from horses’ manes and tails was considered too smooth for the best plaster. Instead, shorter hair from the horses’ bodies was used, in addition to pig hair, cow hair, or vegetable fibers. Modern plasters often use synthetic fibers or fiberglass.

Lime plaster must “cure”; it loses water and sets slowly, over a period of weeks or years. The plaster would need to set between coats; depending on the materials, the weather, and the techniques, it might take hours, days, or weeks. After the plaster was installed, it could not be painted until it dried completely—which could take as long as a year! So, plastering could add considerable time and expense to the construction of a house.

Plasterers were skilled laborers who needed experience and judgment and were comparatively well paid. As well as walls and ceilings, they made the elaborate plaster decorations which came into fashion at the end of the 18th century and remained there, changing styles with the times, until the early 20th century. Medallions and coffers were made by casting plaster in a mold in a workshop and then attaching the resulting shapes to the ceiling of a room. Moldings were made on site by passing a template over wet plaster; the molding took the shape of the template.

As the 19th century went on, plastering advanced. Originally, builders had put in trim first and laboriously leveled the plaster around it; in the early 19th century they started using wooden “grounds,” leveling the plaster to them and then placing the trim on top. (This is one way to date a house or a renovation). Metal lathes were patented in England in 1797, though they did not become common in the United States until end of the 19th century.

From the 1890s, plasters made entirely of gypsum began to be used. Gypsum plaster is made by heating the mineral gypsum (calcium sulfate dihydrate) and removing the water to form a fine white powder (calcium sulfate hemihydrate). When this powder is mixed with water, it reacts to form gypsum again and hardens rapidly. At one time the best-known gypsum quarries were in Montmartre, Paris; thus, “plaster of Paris.” 

Gypsum plaster was not new—it was used in the pyramids of Giza—but in 18th and 19th century America it had been used only in molding plaster and as an additive to the finishing coat of lime plasters. The new all-gypsum plasters set much more quickly than lime plaster and quickly gained popularity.

The true advance in plastering, however, was drywall. Drywall is a layer of gypsum plaster sandwiched between two layers of paper. It is much faster and cheaper to install than plaster and requires no drying time at all.

The earliest forms of drywall date as far back as the late 19th century, but it became increasingly common in the United States between the starting in the 1930s. By the 1950s nearly all new houses used drywall rather than plaster.

Sources

J. Frederick Kelly. Early Domestic Architecture of Connecticut. New York: Dover, 1924.

Mary Lee MacDonald.  “Repairing Historic Flat Plaster Walls and Ceilings.” Preservation Briefs #21. National Park Service Historic Preservation Services, October 1989. https://www.nps.gov/tps/how-to-preserve/briefs/21-flat-plaster.htm

International Correspondence Schools. Masonry, Carpentry, Joinery. New York: Eaton and Mains, 1903.

Edgar de N. Mayhew and Minor Myers, Jr. A Documentary History of American Interiors from the Colonial Era to 1915. New York: Charles Scribner’s Sons, 1980.

Adam Weismann and Kathy Brice. Clay and Lime Renders, Plasters and Paints. Green Books: 2015.

David Flaharty, “Plaster,” in Heritage Preservation and National Park Service, Caring for Your Historic House. New York: Harry N. Abrams, 1998.