Losing Colorado’s Manitou Sandstone

Last night Form+Works met with the Home Owner’s Association of Charline Place, a condominium building in Denver’s Pennsylvania Street Historic District (if this sounds familiar to any out-of-towners, the District includes the famous Molly Brown House Museum). As you recall, they were one of the State Historical Fund’s 2017 Mini-Grant Recipients that we announced a couple of months ago.

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The Charline Place project will be an exterior evaluation of the historic windows, brick and Manitou Sandstone masonry. The project will provide a preservation plan for the HOA to utilize to focus their efforts in a prioritized and manageable way.

We are excited to work with Historic Denver and add Charline Place to our list of Manitou Sandstone buildings we’ve been fortunate to work on. The thing that makes Manitou Sandstone so unique is that it is one of Colorado’s “extinct” materials. Extinct is in quotes because technically the stone isn’t gone….but it would likely be pretty frowned upon to start quarrying right in the middle of Garden of the Gods, one of Colorado’s designated National Natural Landmarks. Needless to say, the only source of exact replacement of Manitou now would be to deconstruct another building, which as preservationists, we would be vehemently against.

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At the turn of the 20th century, the stone was quarried and utilized for countless buildings around Colorado. It is a beautiful stone with a consistent red-orange color. Unfortunately Colorado’s drastic freeze-thaw cycles take a significant toll on sandstones of all kinds, but Manitou, although beautiful, was not one of the most durable stones. The face of the stone tends to “sugar”. That process is exactly what you would imagine. As a sedimentary rock, sandstone is formed by grains of sand being pressed together over time. Since there is no binding material holding the sand together, the durability of the stone is really subject to the amount of pressure it was formed under.

What we have seen on past projects and now on areas of Charline Place, is that there was a campaign – sometime in the 60s and 70s (what we now think of as the “Preservation Dark Ages”) where sandstone buildings were parged  (application of a layer of concrete or stucco)  with the thought that this would stop the deterioration. Unfortunately, what we are seeing is this actually increased the deterioration of the stone more dramatically. You will see areas that haven’t been parged are often in great shape and areas with parging can cause the entire face of the stone (sometimes several inches in) to fall off.

As our project at Charline Place gets started we will be sure to better illustrate what we are describing. Be sure to keep up with our Instagram and Facebook pages for progress updates.

 

 

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