The problem seems to be with the water line that comes into the building and travels up the wall. This waterline is almost completely imbedded in the wall but not totally and the black mold grows just where the water line is. (area of about 3" in width by 6')
Our home was built in the early 60's and isn't too well insulated. The basement wall would be of concrete bricks, then metal lathe then plaster and I have no idea if there is a vapour barrier installed. We can not check the condition of the wall from the outside as there is a concrete planter built in front of this particular wall.
I have used a scrub brush and a strong solution of bleach in the past but the mold always returns. I have noticed though that when I put some drywall compound in cracks in the surrounding area, where the compound spread into the line of the mold it seems to have retarded the mold growth.
My husband suggests that we dig out around the water pipe and expose it.
Suggestions would be very much appreciated.