“While they studied biochemistry on the inside, they fought it on the outside.”
I think that’s my lead for this story I’m working on about mold removal (with a PROSOCO product, natch) on the O.T. Hogan Biological Sciences Building at Northwestern University. It’s a great building. The exterior looks (to me, anyway) like concrete, which is a hallmark of Brutalist architecture, but it’s really limestone.
Limestone, being biological in origin, is a food source for mold, and by 2009, the O.T. Hogan Building had grown a pretty good crop of it.
I did some research to see if I could identify exactly what kind of mold it is on the building. None of the technical people I showed the photos to wanted to go out on a limb — they all said it would be safest to identify the stains simply as “biological staining.”
Being blissfully free of any scientific credential that could suffer if I was wrong, I plunged blithely ahead with my research.
First stop — a useful website called inspectapedia.
Inspectapedia helpfully identified black staining on stone as often coming from a “cyanobacteria” called Gloeocapsa sp.:
Black Staining & Stone Damage from Cyanobacteria – Gloeocapsa sp. and fungi
Black stains on stone are quite often caused by a cyanobacteria (see Catalog of Substances that Alter Stone, Glass, Steel) Gloeocapsa sp. that not only stain the stone black, but also increase water absorption by penetrating veins in the stone (or marble, for example) leading to honeycomb weathering damage to the stonework. Wet stone exposed to either freeze-thaw cycles or heating by bright sun can be spalled or cracked by these forces.
So I Googled Gloeocapsa sp. by itself and with “on limestone” and “historic architecture” and other search-phrases I thought might be relevant. I was looking for accounts or photos of Gloeocapsa similar to what I alread had.
I found lots of scholarly papers, such as Biodiversity of cyanobacteria and green algae on monuments in the Mediterranean Basin: an overview that indicated Gloeocapsa sp. played a major role in the world of staining calcareous building stones — but I found virtually no photos like the O.T. Hogan Building.
I also discovered that a relative — Gloeocapsa Magma — causes those black stains on asphalt shingle rooftops. It turns out limestone is a component in asphalt shingles, and Gloeocapsa loves limestone.
I’m now pretty confident Gloeocapsa sp. was the culprit on the O.T. Hogan Building. If you’re a mycologist, or have some other pertinent expertise, feel free to update me. I would love to hear from you!
JSL Masonry Restoration of Franklin Park, Ill., used Enviro Klean BioWash to clean it off.
But that’s another story.
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