When we think of cement, it’s usually portland cement, which is made from limestone and clay. In Minnesota, we have to import portland cement because most of the carbonate rock here is either dolomite or dolomitic limestone. It contains magnesium, which oxidizes to form magnesium oxide (MgO) in the cement kiln. The bad news is that when you make concrete, the MgO expands when it mixes with water. That leads to cracking and disintegration of the concrete. But before the invention of portland cement, there was natural cement. And there was a time when not just one, but two, companies manufactured it in Minnesota.
What is natural cement?
Unlike portland cement, natural cement comes from a single rock source with the right chemistry to produce hydraulic properties. That is, you can mix it with water to form a hard material that will not dissolve in water. Of course that means you have to find a rock with just the right chemistry. With portland cement, you can adjust the proportions of the limestone and clay–and possibly other ingredients–to get the right chemistry. Another difference between the two is that the clinkering temperatures are much lower for natural cement.
Natural cements originated in England in the 1750s. John Smeaton developed a hydraulic cement for the reconstruction of the Eddystone lighthouse off the coast of Plymouth. In the 1790s, Joseph Parker developed and marketed Parker’s Roman Cement. Natural cements were exported to the United States until the discovery of cement rock closer to home.
Following the War of 1812, Canvas White went to England to study construction practices there, including the use of hydraulic cements. On his return to the United States in 1818, he found a deposit of cement rock in Madison County, New York. He produced and patented a natural cement for the construction of the Erie Canal.
His discovery prompted a search for cement rock in close proximity to other infrastructure projects. By 1900 there were over 70 cement plants in 17 states. Notable structures that used natural cement include the Brooklyn Bridge, Fort Sumter, Fort Knox, and the pedestal of the Statue of Liberty.
I’ve studied historic mortars from around the country. Having identified several natural-cement mortars in Minnesota, I wondered where they came from. I learned that two plants in Minnesota–one in Mankato and one in Austin–had produced natural cement. Mankato Cement Works opened in 1883 and Austin Cement Works in 1893.
Captain John R. Beatty, who owned a lime quarry in Mankato, discovered a suitable cement rock. His discovery piqued the interest of the Standard Cement Company of New York, which built the Mankato Cement Works in 1883. Beatty experimented on the cement rock in his kitchen–a common practice at the time.
Mrs. Beatty, better than anyone else, can tell of the numerous manipulations carried on in the house–much to her discomfort. But she could not help rejoicing with him when she finally heard our geologists’s cry, “Eureka”. — Mankato: Its First Fifty Years, 1902
By 1886 the Mankato Cement Works was the largest in the United States. The plant had five kilns with a total capacity of 1000 barrels per day, and a mill that could grind 1500 barrels per day. (A barrel of cement is 4 ft3.)
…the mortar from this cement became exceedingly hard and stone-like in character, whether above or below water, and withstood to a remarkable degree the effect of alternate freezing and thawing–Robert Lesley, History of the Portland Cement Industry in the United States, 1924
Because the plant had easy access to a rail line, it was easy to ship the cement far and wide. Projects that used cement from this plant include the capitol buildings in St. Paul and Denver, the Minneapolis reservoir, the Chicago Theater and the Wrigley Building in Chicago, and numerous paving and railway projects.
“The bond that guarantees the wall”
After 1900, portland cement began to eclipse natural cement. Its advantages over natural cement, namely better performance and quality control, led to the demise of the natural cement industry. As a result, the Mankato Cement Works began to focus on masonry applications. The name of the company changed to Carney Cement Company around 1907, adopting the slogan, “The bond that guarantees the wall.”
Carney Cement Company continued to supply its masonry cement to large projects across the United States until 1952. At that time there were only nine plants producing natural cement. Today only one such plant remains, Edison Coatings in Plainville, Connecticut, primarily for restoration of historic buildings.
If you’re restoring a historic building, Beton can develop a mortar that will match the properties of the original. Contact us.
Here’s a video tour of the Capitol building in St. Paul.