Condensation. There is no way to fix it-----other than climate control----which is not feasible due to opening the garage door. It will only happen on days when the humidity is high, nights were relatively cool and the days hot.

You should also check the downspouts. Make sure they are clear. If they dump on the ground, make sure they are extended at least 4' from foundation.

Michael

It's difficult to stop the floor from sweating, however you can control it to some degree. I had the same problem.
I went to the local K-mart, bought a small, bedroon ceiling fan with no light on it, and mounted it to the ceiling of the garage and wired it to the house wiring. Now it stays on all the time, and when the air is constantly moving in there, it evaporates the moisture rather quickly. We also noticed that it eliminated the musty smell. That was 10 years ago, but at that time I think I paid 25 bucks for the ceiling fan. I think they're still about that price.

What's happening is the dewpoint outside is well above the temperature of your garage floor. Where we live, if we get a real humid day in late May with a dewpoint above 60 deg, our garage floor (temp in the 50's) will form all kinds of condensation as if it rained inside. As the summer wears on and your floor warms up, you will see less of this condensation. No cure for this other than moving your garage onto a new slab that is well insulated underneath with dense foam. My neighbor just put in a garage with a heated slab - that would be my dream garage floor.

I like that ceiling fan idea! I'm going to do that with my garage...today! Thanks for the tip!

Michael