We just bought a two-family in a Boston suburb. There was evidence of minor water in the basement which the home inspector thought would be remediated thru some minor regrading. We foundation is poured concrete below grade and concrette block above grade. We scrubbed the basement walls with a wire brush and painted the basement with Dri-Lock. We also had the leaky windows replaced. All was well until we moved in and set up an electric dryer, properly vented out one of the new windows. Now there is a black powdery substance growing in the two dampest areas. It is much worse on the poured concrete. HELP! Any suggestions? I am loathe to call one of the mold remediation sites since I am sure they will exaggerate the issue.