I bought a 1927 house last year and, afterwards learned I'm especially sensitive to mold and this house has plenty of it. I've eliminated mold everywhere I've found it except in the inaccessible crawlspace under a kitchen and bedroom addition (1960s? 70s?). I've fixed leaks and replaced drywall, ductwork, etc but I can still smell mold coming up from the crawlspace, which has no access panel but several vents. The height ranges from about 10 inches under the kitchen (worst mold area) to 2 feet at one bedroom corner. I don't know how to get rid of the mold under the addition: seal it and find a way to keep it dehumidified? pay someone to spray foam underneath? install ultraviolet lamps somehow to kill the mold? Help!
After killing the existing mould. Ventilation is the answer (usually).
I'm rebuilding a stone wall/underpinning in a large underfloor area (appx. 1.7m high or nearly head height) and it had a serious mould problem a couple of years ago. The guys came in, cleared out a load of old mould infested rubbish and then installed an air pump with a series of metal ventilation ducts with rubber outlets.
The system measures humidity and temperature and then draws in air from outside and pumps it through the ducts into the whole basement. I think they aim for 50 to 60% humidity and around 10 to 12 degrees C down there.