Mysterious moisture in garage
I’m trying to diagnose a mysterious moisture issue in a garage. This is an attached garage with living space above (I know, I know – no cars are stored in the garage) located in Mass. Whenever there’s a large rain or it’s particularly humid – including during the winter – there’s an excessive amount of moisture on the garage slab. It can be wet to the touch. It seems to spread from the garage doors back into the garage and follows a pattern that roughly approximates the tire tracks where somebody would have pulled their cars in. It’s a problem because the humidity is way to high in the garage. Things are getting moldy and I worry about the moisture moving into the house.
At first, I assumed the moisture was moving up through the slab (i.e. no vapor barrier). But if there’s something impermeable on the slab like a garbage bag or styrofoam, then the slab will be dry beneath that. I assume this means the moisture is not moving through the slab.
So I’m thinking it’s either condensation or that the water is somehow being wicked back from the edge of the garage (if the door is closed, there’s still an exposed strip of concrete). Either way, it seems odd.
Any thoughts on what would explain this? And any recommendations on how to remedy this situation? Would a sealer or epoxy coating help here? Would installing an exhaust fan in the garage help dry things out more quickly and prevent mold?