We live in the first floor of a corner Brownstone in Brooklyn. We also have a finished basement which is 100% below grade. We have spent considerable time and money to turn the basement space into a home theater and office (aka The Man Cave: The Happiest Place On Earth).
There was initially a wooden subfloor covered with engineered wood in the basement. We had this ripped out when after the basement flooded a few times and a musty smell suggested and later confirmed the presence of mold. This floor was replaced by a new concrete slab with a beautiful, glossy painted and sealed finish.
I have taken some measures over the years to prevent future floods (serviced an ancient back flow trap that was allowing sewer water to come out of the basement toilet and shower) and the basement hasn't flooded for a few years. A humidifier is constantly set for 60% humidity.
But the musty smell has persisted and the most likely source is a wall in the basement.
The suspect wall is dry wall and studs that covers a foundation wall made up of Manhattan Schist. There is no insulation in the wall and the foundation wall is covered with efflorescence. The wall is 24' and runs along a side street so it is very susceptible to run-off and ground moisture.
Four or five years ago a leak came out from under the drywall. I removed the drywall in that area, sealed the leaking portion of the wall with Quikrete Hydraulic Water-Stop cement and Drylok paint and repaired the drywall. But I suspect the wall is leaking small amounts water fairly regularly.
I'm concerned about mold and mildew, especially with kids in the house. I poked some exploratory holes (12" x 6") in the drywall and found no visual signs of mold. The bottom of the cavity is filled with about 1" of dirt that has crumbled from the wall and it is dry to the touch.
I see two plans of attack...
1. Rip out all of the drywall, clean and Drylok the wall and leave it exposed so that it can be easily maintained as the moisture and efflorescence inevitably reappears.
2. An architect suggested the solution of putting vent holes (12" x "6 covered with return vents) along the top and bottom of the wall to vent the space. But will this just create more airflow for mold and mildew spores to spread to the rest of the house? Will warm air flowing against the colder rocks create more moisture leading to more mold and mildew?