The one "test" culture plate I had that cracked.. i covered the crack with mycopore tape hoping it would help and added it along with the "control" plate. a dark/Black mold erupted on the side of the rim inside the dish. So far the control plate seems unaffected. The bad plate has been thrown in the garbage. Anyway.. oof. So i guess if a plate cracks it cracks don't bother trying to seal it with anything, just pass go, collect 200$ and start over.