Then we came across something that finally made sense… and at the same time made everything even more surprising.
The Real Explanation: Plant Roots
It turns out, it wasn’t mold.
And it wasn’t insects either.
It was actually plant roots.
Yes real roots.
Most likely, they came from a tree or plant outside the building (or possibly even from vegetation growing beneath or nearby the structure). Over time, they found a tiny crack or gap in the construction.