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The plant of the Twin City Brick Co., one of the largest in the State, is at the boundary between West St. Paul and Mendota. The quarry is very extensive, and the kilns have a capacity of nearly 100,000 brick a day. The company produces brick and hollow ware. Brick are burned to about 2,100° F., the temperature varying considerably according to the type of product desired. The types produced vary according to the proportion of upper and lower shale used, to the temperature used in burning, and to the supply of fuel and air at the different stages of burning, resulting in oxidation and reduction. Work was begun in this neighborhood more than 20 years ago and has progressed with many changes in method and organization, and the final consolidation and success have been due largely to the present careful management. Market conditions are of course excellent. Details of manipulation have been patented; and ingenious devices, especially methods of quarrying and a chain conveyor, have been developed that are worthy of careful study by anyone planning to use the Decorah shale. Although the shale burns red under normal and laboratory conditions the color can be altered by controlling the fuel supply and by shutting off the air supply. Fancy brick, front brick, and klinker brick are produced in so great quantities and bring prices so high that the production of common brick has practically ceased at this plant. One of the many interesting special products is an interlocking tile for building block.
Prof. Talbot, of the University of Illinois, who has tested the products made in West St. Paul, reports a crushing strength of 1,100 pounds to the square inch for hollow block about 4 by 4 by 4 inches with vertical opening. The city building inspector of Minneapolis found a crushing strength of 900 pounds to the square inch as an average of 10 tests on hollow
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Blocks 4 ½ by 4 ½ by 12 ½ inches, and of 3,300 pounds to the square inch (minimum 1,775 and maximum 6,250) as an average of 10 tests on solid bricks.
Source:
Clays and Shales of Minnesota
Frank F. Grout with contributions by E. K. Soper
United States Geological Survey
Government Printing Office, Washington, D.C., 1919