Unlike modern paint, which is made with toxic chemicals and VOCs, plaster is a natural and breathable material that is comparatively healthy for the environment. It also works well in historic homes.
Lime and Cement – the Base Coat
A common building technique used for centuries, lime plaster was applied to walls and ceilings with a mix of lime, aggregate, water, and occasionally animal hair. During the early 1900s, homebuilders often added horsehair to the mixture to make it stronger.
Historically, plaster was applied over a layer of closely spaced strips https://www.stallionplastering.co.uk/ of wood nailed to studs called “lath.” The lath helped to stabilize the plaster as it dried. The lath was then covered with a second layer of plaster.
This was done to create a stable, smooth, and flat surface for painting or finishing. This technique was also used to create architectural mouldings such as cornices and ceiling roses.
The lath and plaster process required a long setting period, so it was a time-consuming and expensive way to build houses. In some areas, the lime used for plaster was difficult to obtain. It was sometimes mixed with seashells that were found along the coast, or clay from midden piles that had been dumped by early Native Americans.
As the mixture set, it created a nib or point that stuck to the wood lath. This was called a “stallion” and it was important to the strength of the wall.
Older houses, especially in the South Shore and Boston-area, commonly used horsehair plaster. This was because it was easier to make, and the mixture was stronger because of the horsehair.
Another advantage of horsehair plaster was that it dries faster than other types of lime plaster, which requires a long setting time. It was also less susceptible to cracking or crumbling.
A third benefit of horsehair plaster was that it was very easy to apply. The horsehair was mixed into the lime mixture and was then quickly spread over the lath.
The horsehair was a bridging agent, allowing the plaster to stick to the lath without breaking the wood. It was also helpful for the plaster to hold up to the harsh weather, which would often wreak havoc on the construction of early houses.
This plaster mixture was a staple of many homes in the area until the end of the 19th century. As the building industry grew and technology advanced, horsehair was removed from use, but it is still commonly used in historical restoration projects.
Sand Faced Finishing Coat – the Second Coat
A final layer of plaster with a sand and cement mortar mix proportion of 1:3 thickness is applied to the walls. The mortar is cured for seven days and then a thin coat of sand faced finish is applied on top. This is a very attractive, durable, and water-proof finish.
There are a few different types of sand face plaster finishes, but the most popular is Peddle Dash or Day Dash. It is a thick and smooth surface. It is usually given a decorative zig-zing line, but can also be a simple plain or a simple design.