An Alarming Symptom, Maybe

by Don Friedman on October 23, 2017

Sometimes issues during an investigation aren’t clear. That picture is the entry to an abandoned church and that’s a really odd crack in the floor. I was there to do the most basic type of conditions assessment – hazard to the public or not? – and since the building was closed to use, the only real question was whether it was likely to fall down in part or in whole. The question of what was going on with the floor was not crucial to the question at hand, so I never got a final satisfying answer.

If you click on the photo to enlarge it, you can see that it’s a tile mosaic floor that is buckling upwards. And the last word of that sentence is why the issue is not clear. Gravity is relentless, never ceasing its downward pull, so for a piece of a building to move up requires a constant force in the upward direction. The main crack is pretty much in the center of the entrance vestibule, and before I went in the cellar to confirm the wall location, I assumed that the cellar walls were at the same location as the first-floor walls. (It turned out that assumption was correct.) So the crack appears to be in the middle of the first-floor structure and floors sag downward (if they sag at all) as they age. So what’s pushing up?

The first floor structure is, unsurprisingly for a nineteenth-century church, wood joists spanning between brick walls. The tile floor is on a reasonably thick setting bed. So two possible mechanisms for pushing upward come from material deterioration: rotting of the wood subfloor below the setting bed, or some kind of water-triggered change in the setting bed itself. As a vestibule, this floor probably got wet, even if just a little bit, every time it rained. If the setting bed contained an expansive mineral like gypsum, or the subfloor was protected from rot on its underside but not i=on its top, you could maybe get deterioration that would look like this.

If the side walls were moving in, the floor could buckle up, but there was no sign of such movement in the masonry and it would have been even odder than the floor movement, so I ruled that out.

Honestly, I don’t know now and I never will. The rest of the building was safe enough to pass the simple test I was addressing, so I cut the investigation of this issue short. Part of investigative work is being able to say that the results are good enough to be useful and ending the site visit.

Telegraphing Through

October 20, 2017

Another artistic photo, this time of one face of a party wall in a rowhouse. If you look closely (click on the picture to expand it), you’ll see that the plaster is well-adhered to the brick. The plaster didn’t fall off in that one area, it was removed. Why? Because the presence of that long, […]

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This Is Ungood

October 18, 2017

From a few years ago, some rotting wood beams and a failing brick pier. In 1989, I performed a long and difficult site visit to check on a structure I won’t name (confidentiality is still in place, even after all these years) that had to be reviewed once per year. The fellow who had been […]

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Rising To Failure

October 3, 2017

This is the same building as the unlinteled door – it was chock full of bad masonry conditions. The picture above is just to provide some context. I’m interested in the brick pier in the cellar. Here it is in isolation: There are several possible causes for the visible damage, but rising damp is the […]

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All In The Emphasis

October 2, 2017

I find this article in the New York Times about the recent earthquake in Mexico City to be problematic. To be clear, I claim no special knowledge of the quake itself or of Mexico City, but the building process is the same everywhere. To create a building of any significant size, we need a prospective […]

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Patterns of Damage

September 28, 2017

João Carlos Souza has a primer up on ArchiNet on how to identify problems in concrete buildings based on crack patterns. Putting aside some bad translation from Portuguese to English* it’s quite good and can help identify damage when used as intended. Mr. Souza does not explicitly state the assumptions that went into his visual […]

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Failure In An Expected Pattern

September 20, 2017

The animated picture above is from The General, a 1926 Buster Keaton movie. (Click on the picture to enlarge it.) In the era before computer graphics, and when the use of scale models for special effects led to disappointing results, Keaton got a realistic train crash in the obvious manner: he crashed a train and […]

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Anna Karenina in Concrete

September 10, 2017

Tolstoy said that “Happy families are all alike; every unhappy family is unhappy in its own way.” This principle can be applied to buildings: every building in good condition is alike, every failing building fails in its own way. The white paint on the concrete does a great job, in my opinion, of highlighting where the […]

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Sidewalk Vaults and True Obsolescence

August 14, 2017

For people unfamiliar with sidewalk vaults, the illustration above, from 1865, might seem plausible, but it’s actually Daniel Badger’s fantasy of how he could sell more iron. The left-hand side is reasonably accurate for mid-1800s vaults: the facade columns extend down past the plane of the sidewalk, marking the separation of the cellar proper from […]

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