• Sarah Dezember

Tracing Your Bungalow's Concrete and Plaster

This week, we'll be continuing our series after pinning down the origins of our renowned Chicago Brick, and tracing the history of your bungalow's concrete and plaster!


Can you name all the places concrete is used in your house? How about plaster? Do you know what those materials are made of? What about where those materials came from?


There’s a lot that goes into making a house! Today, we’re going to learn more about concrete and plaster, how these materials are made, and how they end up in your home. Let’s dig in and take a closer look.


Concrete is what’s holding your home up. It’s the backbone of your home.

Tracing the Origin of Your Bungalow’s Concrete

Not only is your foundation made of concrete, but so are your front steps, your porch, and even your basement. In other words, concrete is what’s holding your home up. It’s the backbone of your home.


Concrete is made up of three “basic” components: aggregate, water, and cement, which means concrete doesn’t come from one place. Each ingredient is sourced from a different location and then brought together to make concrete. This seemingly simple formula becomes a lot more complex as we explore what each component is made of and where its elements come from. Let’s dig a bit deeper into each component:


Aggregate

Aggregate makes up about 60-80% of concrete and is typically composed of sand, gravel, limestone, or other crushed stone and then binds with a paste which is made of cement and water.


Sand and gravel resources are usually mined from floodplains, alluvial fans, shorelines, and sand dunes. Sand forms when rocks break down from weathering, which most often occurs from wind or water. Like clay, river channels and glacial deposits provide for the richest amount of sand and gravel production.


Image by Sarah Dezember

Sand, which we most often don’t associate with the construction of our homes, is one of the world’s largest mining endeavors. The states leading in sand mining, in ascending order, are Wisconsin, Illinois, Texas, Minnesota, Arkansas, Oklahoma, Missouri, and Iowa. Sand and gravel are most commonly mined in open pits. The mining cycle starts by removing the topsoil, which is then sorted, washed, dried, and then transported out of the mine. The remaining materials are then used to backfill the soil.


Image by Sarah Dezember

Aggregates are often made from limestone as well, especially in Illinois where there is an abundance of the mineral. A quick history lesson will help us understand why. About 425 million years ago, before Illinois was pushed north by tectonics, it was covered in a shallow, tropic sea called the Silurian Sea. At the base of this ancient sea was a rich and diverse coral reef. The coral took in sea-water and processed out the lime, creating lime deposits that would harden and produce limestone.


Limestone is mined in open quarries from places like Thornton Quarry, which is one of the world’s largest limestone quarries, and only about a 40-minute drive south from downtown Chicago. Limestone is typically extracted through a blast, or via mechanical extraction, depending on the hardness of the stone. Once it’s removed, it is crushed on-site, then transported to the manufacturing site to be further processed.


Image by Sarah Dezember

It’s probably safe to assume that the aggregates used in the concrete of your bungalow’s basement or front steps are coming from within the state. But, there’s a chance it could have come from as far as Wisconsin or even Minnesota!


Cement

Cement is a fine powder made up of crushed minerals such as limestone and our friend we met earlier - clay. When mixed with water and aggregates, cement acts as a binding element that helps concrete to harden. Cement only makes up roughly 10% of concrete.


Image source: State of Illinois State Geological Survey
Image by Sarah Dezember

In 1915, there were five major cement plants in Illinois. Today, there are three. Cement is expensive to transport because of its cost and because it’s likely to dry out and crack if it’s traveling long distances. That means, the cement for your bungalow likely came from one of these plants. Although, it is important to note that one of the largest cement plants in the world is located in Alpena, Michigan. Because Michigan is also home to many limestone quarries, we can assume that this cement producer often sourced its aggregate from nearby quarries to cut down on transportation costs.


Air and Water

Two often overlooked elements that are crucial in the manufacturing of almost all materials are air and water. These two are especially important in the production of concrete. Water is needed to hydrate the cement in order to make it “workable.” Air helps to make sure that the water can move and escape. If there is too much water in your concrete, the water will freeze and expand, which leads to cracking.


Gypsum is prevalent thanks to one of six prehistoric seas that flooded the Michigan Basin between 600 to 230 million years ago. As the sea dried up and evaporated, it left behind large deposits of gypsum which would much later become the interior walls of your home.

Tracing the Origin of Your Bungalow’s Plaster

Plaster acts as a protective coating for your walls. It also acts as a canvas where we can express our personal styles onto our homes, choosing color schemes and setting the moods of our indoor life. It’s how we make a house our own.


In early American architecture, plaster was typically made from a mixture of lime, sand, water, and horse or cattle hair. But, that may not be the case for your bungalow. Our friendly neighbor, Michigan, has some of the richest gypsum deposits in the world. Gypsum is a soft material found in layered sedimentary deposits, and since 1930, it has been the most commonly used rock in plaster production.


Image source: L.M. Sommers, Michigan: A Geography (1984).

Gypsum is prevalent in Michigan thanks to one of six prehistoric seas that flooded the Michigan Basin between 600 to 230 million years ago. As the fifth sea, known as the Mississippian, dried up and evaporated, it left behind large deposits of gypsum which would much later become the interior walls of your home.


In its natural state, gypsum is found inter-layered with limestone. So, there’s no surprise that it’s excavated using the same process as limestone. In order to transform gypsum rock into gypsum plaster it is pulverized and then heated at 248℉ for one hour to remove a portion of its water content. Water is later reintroduced to the crushed gypsum mixture to make it pliable and ready for application.


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Open pit gypsum mine near National City, Michigan operated by the National Gypsum Company. Image source: Mountain Scholar

The interior walls of your bungalow were most likely constructed using a technique called plaster and lath. Thin strips of wood (lath) are nailed directly into the open wall studs. Lath boards are often made from the discarded portions of larger pieces of wood used for external walls or furniture. They can be made from any type of softwood but most commonly were made from cedar, pine, or fir. (Don’t worry we’ll be discussing wood more in-depth in the next blog post!)


Once the lath is nailed to the wall studs, it is then embedded within three layers of plaster. Once the three layers of plaster have hardened, it is ready for primer, paint, and the adorning of your choosing.


Tune in next week for the final installment of this blog series when we discuss wood!

Sarah Dezember is currently pursuing her Masters in Architecture with an emphasis in Interior Architecture from the School of the Art Institute of Chicago. In this blog series, she uncovers the hidden histories of materials used in our bungalows to help us understand what’s at the heart of our homes.

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