i know this is late coming, but i would use a garage floor paint. even then it may do it. around here this is a very common issue as we have high ground water and high humidity. sometimes paint/sealer works, sometimes it does not.

I've heard that the sealants won't stick if your floor is wet. Which sounds like yours is.

Do a test by putting down a sheet of plastic over the concrete, held down by duct tape.

It's possible the moisture is condensation from the air, not weeping from the ground.

You must have a high water table or your moisture barrier has failed. Maybe your shop is very old and doesnt have a moisture barrier. Paint surely will peel of quick. In your case even the best epoxy or polyaspartic system would fail. You need to waterproof it first with a vapor emissions primer, then apply an industrial coating system. Any industrial flooring company should have access to this type of formula. Expect to pay a good price though. A complete system in your case could rum from $10-$15 per sqft.

Check around the perimiter of you shop and make sure the ground is sloping away from the slab. Quite a few hundred gallons of water can fall from that roof and seep under the slab. You might have to ditch around the shop and install perforated plastic pipe to dirct the water away. Or install gutters and downspouts directing the water away. If you don't get rid of the water problem you will be wasting your money on coatings as they will probably just peel up. Good luck, Mainah.