Plaster interior finishes are a large topic of interest in historic preservation work. But, as an engineer, I’m not usually involved with that work. On the other hand, plaster is of great use in engineering investigations as a building-wide diagnostic aid.
The wall on the right is plaster finish over brick, and is structural supporting the building’s floor joists. The wall on the left is an interior partition separating two rooms and is non-structural. Rather than supporting load, the partition on the left rests on the floor joists below. When the floor joists move, for example under repeated cycles of loading in the ordinary use of the building, the partition moves with them, while the brick wall stays still.
In this case, neighboring construction moved the other bearing wall (out of the picture frame, some fifteen feet off to the left) down slightly so that the joists now slope off to the left. The partition followed and the brittle interior finishes cracked badly. The building itself told us what went wrong before we had the opportunity to even investigate the foundation movement.
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