Vol. XIX No. 3 - FALL 2008

By: Kathy Gemperle

Concrete has become the building material of choice in the most recent building boom. It has many advantages over traditional building with lumber and brick. Concrete is strong, durable, fireproof and inexpensive. Because the blocks are larger, it takes less mortar and less work to put up a concrete block wall. As we look at the new construction in concrete, a change is apparent. The current blocks seem to have more uneven finishes, much like the rusticated Bedford Limestone of the typical Chicago grey stone buildings. Today, when we see the concrete sides of many new Chicago eight flats, we see a concrete that is imitating stone.

This use of concrete, and even this design of the blocks to look like rusticated limestone, originated in 1900 with the invention of a hand operated machine to cast concrete to look like stone. The inventor, Harmon S. Palmer, succeeded in making a molding machine out of cast iron. In 1902 he founded the Hollow Building Block Company and, by 1904, his company was producing about 400 molding machines per year. The interest in this new and inexpensive method of producing building materials grew by leaps and bounds. Part of the expansion of this industry was the improvements in a reliable Portland cement. Cement is the most important element in concrete, which is made up of stones, aggregates, sand, water and Portland cement. It is the cement that hardens into concrete.

Initially, the size of the blocks depended on the molding machine. This molding of blocks could take place at the construction site. It seems to be a slow process. The molding had six sides and a patented way to open the mold so the block could be removed. Workers filled the mold by hand, tamping down the material around the hollow openings in the middle. The operator then closed the mold and, using levers, changed the position of the mold to a different side. Then the end doors were released and then, using another lever, the block could be released. According to an ad in the 1910 Sears and Roebuck Home Builders Catalog, one man could make 125 blocks a day. The machine was available through Sears and ranged in price from $42.50 to $63.75. Also, by 1910 there were a variety of face designs and decorative details available for molding. The most popular design, standard on all machines, was the rock face rough cut surface that looked like quarried stone.

Of the concrete blocks manufactured before 1915, nearly 75 percent were used for foundations. These blocks facing out were in the rock face design. If the blocks were used for partition walls in the interior, they were smooth faced. By 1924 the Concrete Block Manufacturer’s Association, the Concrete Producers Association and the Concrete Block Machine Manufacturers Association were able to establish standard sizes for all blocks. In 1930 the size became 8” x 8” x 16”.

With the development of a lighter weight block in 1917 by Joseph Straub (sometimes called a cinder block), the manufacturing increased. Cinder blocks had some additional properties including the ability to be nailed into and could be faced with traditional materials like brick. This process of improving the material and automating the manufacturing process continues to the present day.

Although the use of concrete as a construction material is very popular, there a few problems. The initial block shows some shrinkage as it cures and hardens. It also changes when exposed to temperature and moisture changes. These problems show up as cracks. Another problem is spalling (which also occurs with bricks), an imbalance in the initial mix proportions. Sometimes a kind of efflorescence shows on the blocks as a problem with moisture and salts in the curing process or over time. These problems have been given a lot of study and a variety of conservation techniques have been developed.

Our 2008 Home Tour featured an all concrete block building on Highland Avenue. The owner, Tim Lynch, has provided us with his research on the material in the book “Twentieth Century Building Materials Edited by Thomas D. Jester.” He has also provided a copy of the Sears and Roebuck catalog, which has been reprinted by Dover Publications. Among the information that we found about his building was that the architect was A. E. Norman, who had an office on Devon. Norman was a well known architect in Edgewater and Andersonville. Many of his buildings show a fondness for limestone details. So it is of great interest that he was involved in a project to build three concrete block two-flats on Highland. The date of the buildings is 1907, so we can presume that each block was made by hand using the new pressing mold machine. The entire exterior of these buildings is concrete block, not just the façade like many Chicago two-flats. These are remarkable buildings. Unlike the greystones, these building have a hint of a warmer earth tone. Also, there are decorative eagles on the façades.

A brief search for other concrete block buildings came up with only two on the 1700 block of Rascher. These two buildings are next to each other and have the concrete blocks only on the façades. It may be that there are more homes in the area with concrete block foundations or concrete block used on other parts of the buildings. If you know of one please contact us via our web site.