Bleach works fine. Most of the commercial products you can buy in stores are bleach-based. Such as Tilex, mentioned above, which also works fine. One tip: To prevent a recurrence, make sure the area is dry. Mold grows in moist, dark areas. (And the warmer it is, the more the mold likes it.) You were right to try exposing it to sunlight, but that's more a preventative. It won't kill it. So, when you've killed it, make sure you identify the source of the moisture. Then stop the moisture. Also, you may have to treat the area several times, or treat the surrounding area. Problem is: Mold spreads with spores. So there may be (very likely are) spores elsewhere in the garage where, perhaps, the mold isn't growing. But over time, breezes will redistribute the spores. And if the spores land on a most area--especially moist and dark--they'll grow. Spores can last for months or longer. So, as best you can, wipe everything around there with a diluted solution of bleach. Find the source of moisture and eliminate it. And watch out for recurrences. Hope that helps.