How do I prevent basement mold?

Keep liquid water out and keep the air under 60 percent relative humidity, closer to 50 percent if you have already had growth. That means downspouts, grading, a sump that works, and a dehumidifier with a hose — not a bucket you forget in July.

Do not finish a damp stone cellar with carpet and glued-on insulation. Do not store cardboard on the slab. Those two choices cause as many calls as dramatic floods.