"SHSI Certificate of Recognition"
"Best on the Web"

Encyclopedia Dubuque


"Encyclopedia Dubuque is the online authority for all things Dubuque, written by the people who know the city best.”
Marshall Cohen—researcher and producer, CNN

Affiliated with the Local History Network of the State Historical Society of Iowa, and the Iowa Museum Association.


From Encyclopedia Dubuque
Jump to navigationJump to search
Rock wool blocks.

GENERAL INSULATING AND MANUFACTURING COMPANY. Located in three of the former MILWAUKEE RAILROAD SHOPS, General Insulating and Manufacturing Company opened for business on June 17, 1937. On the first day, twenty-five employees went to work, but company officials hoped to have fifty by the first of the next week. (1)

General Insulating was the world's largest exclusive manufacturer of rock wool products. The grade name for the company's products was "Gimco.

The limestone used would come from quarries in the area of Dubuque. Inside four cupolas at the Dubuque plant alternating layers of rock and coke were laid. The rock was melted in the lower portion of the cupola by heat generated by the coke under forced draft. From a point near the bottom of the cupola the melted rock flowed into a blast of steam which shredded it and the treated the stone with a patented process. A blast of steam blew the shreds of treated rock into a chamber when the "wool" fibers form in passing through the air. Under controlled temperatures they were cooled.

When the fibers were compressed, they formed an insulating product with entrapped air space volume of between 90 and 97%. This air space volume gave the rock wool its insulating properties. Rock wool was free from all shrinkage and expansion under all temperatures and moisture conditions. It was fire resistant.

The Dubuque plant was expected to produce an average of six carloads of rock wool daily. The firm would be one of the largest producers of tonnage in the city and one of the largest users of Dubuque products.

Among the products of the local firm would be refrigerator insulation, rock wool sound absorbing panels, insulating blankets for construction, rock wool insulating and finishing cement, pipe insulation, and insulating blocks. (2)



1. "New Rock Wood Firm Launches Its Production," Telegraph Herald, June 17, 1937, p. 1

2. "Dubuque Gets Rock Wool Factory," Telegraph-Herald, April 4, 1937, p. 1