We have an old 1939 brick two-story house with a cement brick foundation and basement. My wife hates basements, so a couple years ago, we started finishing it by putting up studs, plastic, insulation and drywall. It's not mudded yet.

Since then, there is a musty smell on the FIRST floor in one corner of the house. There is no smell in the basement, but sometimes there is one spot on the stairs when walking up from the basement that I smell the same smell.

In February (winter), I took one of the walls a part and I didn't see any mold on the wall under the corner that smells.

In the past, we've had to run dehumidifier in the basement in the spring/early summer (when no AC) to keep a constant humidity. It wasn't too hard to keep it under 60%rh, so it wasn't a terribly damp basement. Now, we don't need to use the dehumidifier much at all, which makes me think it's all just trapped in the wall.

Anything else I'm missing? Any suggestions? I'd like to make sure this is all ok before I try mudding the walls. I'd sure hate to have to pull down all the walls.

Thanks!

I suspect the odour is taking the easiest route to your nose. Not all mould is visible. And not knowing your construction, details, it 's possible that the mould is growing under the base plates for your walls.

Are you sure it's not sewer gas from a dry trap or unvented appliance? The bathroom in a rental house I owned always had a dank smell. I attributed the aroma to the hygienically challenged university students who lived there. But when they moved and I renoed, I found the appliances were vented into the wall, not into a stack.