THE STRANGE CASE OF MYSTERIOUS MOLD

When you’re renovating a building, the last thing you want to find is mold. And when you have tenants living there full time — particularly tenants who may be susceptible to greater health risks — you definitely don’t want to find mold. A luxury senior living center in a large South Texas city found themselves in this situation, and they wanted to determine what went wrong and how they could fix it.

A few months ago, a company I work for as a subcontractor sent me out to answer these questions. The 19-story center was in the process of removing old vinyl wallpaper from the second floor interior hallways when they discovered mold growing beneath the wallpaper. Going in, I had two jobs. First, I needed to come up with the scope of work for mold remediation so the client could find a contractor to remove the mold. Then I needed to determine why mold was growing in the corridors to begin with.

This building presented an interesting challenge. I could understand mold growing on the inside surface of exterior walls, but finding mold on the interior hallway walls was a bit strange. There had been no water leaks, and based on the pattern of growth — beginning at the floor with columns of mold stretching to the ceiling every few feet — I could tell the mold hadn’t been caused by custodians using too much water when mopping. Solving this puzzle required other skills developed over years of training.

After assessing the situation, I was able to determine “stack effect” was to blame. Sometimes called “chimney effect,” the problem occurs when warm air rises inside a building. Hot air is forced out of the building at upper floors, and this results in the building sucking cold air in at the lower floors. In South Texas, you always have 20–25 mph winds blowing off the Gulf of Mexico, which affects the air movement in the building. In this case, if you stood by the entrance door and opened it just a crack, stack effect within the building pulled the outdoor air past the door with such force that it felt like a wind storm. This often explains why a resident living on the second floor is always cold, no matter how high they turn up the heat. Meanwhile, someone on the 19th floor of the condominiums never has to turn on their heat in the winter.

The shifting air pressure of stack effect doesn’t cause mold, but if a building isn’t properly sealed, it can draw up moisture between the floors. Following a hunch, we had some ceiling tiles removed from the first floor ceiling and found pipes penetrating the slab (floor) of the second floor, exactly where the tall columns of mold grew.

Knowing how the problem originated, it was easy to test and prove air leaks as the source of the mold they were experiencing. We then offered suggestions to the property manager to keep the mold from returning.

This was one of the more unusual and challenging projects we’ve had in a while, and it was fun to investigate. Also, it’s nice to know all my years of training and experience still come in handy for my commercial building clients!