Windsor Plaster Company

The Windsor Plaster Company operated a number of historical quarries in Hants County and, somewhat unusually for Nova Scotia, a calcining mill.

Calcining gypsum means to heat and partially dehydrate it. It's part of the process of turning gypsum into plaster so it can be used in products like wallboard, mouldings and casts.

Most Nova Scotia gypsum has been exported in crude form, meaning the rock was crushed to various sizes, mostly ranging from “man-sized” rocks (rocks one man could carry) to chunks a couple inches in diameter, depending on the era and the needs of the end-user.

However, most Nova Scotia gypsum has not been calcined before being exported to the eastern seaboard of the United States because it has usually made more economic sense to do the calcining where the gypsum was also manufactured into plaster or wallboard, and closer to the major markets where most of it is sold.

The Windsor Plaster Company’s calcining mill was one of relatively few exceptions. It was the only calcining plant in the province for a while during the early 1900s. In 1915, there were seven gypsum companies operating in Nova Scotia but the Windsor Plaster Company was one of only two that had a calcining plant.

Its plant grew out of a company established in 1864 by James A. Bennett of Windsor that ground and “burned” gypsum before selling it for building and as fertilizer. Bennet’s operation was one of Nova Scotia’s first attempts to calcine gypsum locally.

In the 1880s, Bennett built a new plant on Windsor’s O’Brien Street and a railway siding was established to facilitate shipping.

The company went bankrupt in the late 1880s and its assets were purchased by C. Henry Dimock (the Dimocks played a major role in Hants County’s gypsum history) and Jessie P. Smith.

Dimmock and Smith established the Windsor Plaster Company and sold fertilizer and various types of plaster to customers throughout the Maritimes, Ontario and Quebec. Some sales were even made as far away as Australia.

When C. Henry Dimock and Jessie P. Smith passed away in 1931 and 1941 respectively, their sons, Milford Dimock and Louis Smith, ran the company until the 1950s.

The Windsor Plaster Company operated a number of historical gypsum quarries in Hants County to supply its plant.

It developed quarries at Ellershouse and St. Croix in 1901. In 1906, the St. Croix quarry was idle while the Windsor Plaster Company instead worked the Mosher Quarry, which was owned by the Windsor Gypsum Company.

In 1912, the company opened a gypsum quarry at West Gore, Hants County.

In 1922, the company started working at the former Wilkins quarry just southeast of Windsor and the George DeWolf quarry in Three Mile Plains. In 1924, it also opened a quarry in Clarksville.

In 1934 the company operated a quarry on the land of Howard Smiley, four miles east of Brooklyn, and in 1939, it opened a quarry on the land of John Fox, one mile west of Newport on the road between Brooklyn and Newport.

In 1944, it ran a quarry on the Veinot property at McKay Section (then called McKay Settlement) and in 1947 it ran a small quarry on the Maynard property in McKay Section.

In 1956, the Windsor Plaster Company was taken over by the Gypsum, Lime and Alabastine Company of Toronto but its quarry operations were shut down in 1958. (The Gypsum, Lime and Alabastine Company also operated the Nappan gypsum quarry in 1959: ).

Domtar Construction Materials Ltd. bought the Gypsum, Lime and Alabastine Company in 1962 and continued to operate the calcining plant.

A 1915 report said the plant included a series of buildings: a boiler house and engine room, a three-storey calcining mill, blacksmith shop, two storage bin buildings 175' X 60' and 100' X 30', office, cooperage, storeroom 75 feet in length and barn.

The power plant consisted of one horizontal return tubular boiler of 100 horsepower capacity, one long stroke, single acting engine with 8-foot flywheel, and a small auxiliary vertical engine used to drive an electric generator for lighting purposes.

After coming from the quarries, the gypsum was stored in large storage bins and from there it was hauled up an incline to the mill as required. The car on this incline held approximately one ton, and this was dumped directly into the hopper for the jaw crusher. This crusher reduced the rock to 1-inch size.

From this crusher it fell, by gravity, directly into a rotary crusher and was then hoisted by two elevators to the top of the building, where it was deposited into two hopper-shaped bins. These bins were directly over buhr mills (grinding stones) that ground the rock down further.

A screw conveyer carried the ground material across the building to an elevator which again elevated the gypsum and placed it in the large receiving bins over the kettles. Two chutes beneath the screw conveyer enabled part of the crushed, uncalcined gypsum to be taken off for use as fertilizer (historically also called “land plaster”).

From the bins over the kettles the gypsum was run by gravity into two ten-ton calcining kettles. When the material was calcined, which took 2-3 hours, the hot calcined gypsum was run by gravity into two cooling pits beneath the kettles.

When cooled, it was again elevated and passed through screens and bolted, with some being reground in a small French buhrstone and then packed as fine calcined plaster. The material passing through the screens was fed to a mixing machine and manufactured into several grades of hardwall plaster. The name Selenite was used a trade name for the product marketed by the company (selenite is a type of gypsum).

The flow chart below shows the process.

Before wallboard/drywall became the most common way to finish walls, walls were usually made of laths (thin, flat strips of wood) with plaster spread over them. Ground gypsum was, and still is, a key ingredient in plaster. This method of making walls died out after wallboard was invented in the United States in 1918 by sandwiching plaster between two sheets of paper.

Today, wallboard is used in most buildings. An average home has about seven tons of gypsum in its walls. Most walls in Nova Scotia contain gypsum quarried in the province.

Safety is the main reason gypsum is in wallboard. Gypsum is 21% water at the molecular level so it slows the spread of fire and helps save lives.

Ellershouse, where one of the Windsor Plaster Company’s quarries was located, was named for its founder, Baron Franz von Ellershausen. He had an amazing life story and career in mining: