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.