Condensation, or moisture out of the air, causes the wet concrete garage floor. A combination of warm air with relatively high humidity coming into contact with the cold concrete garage floor is what causes the “wetness”. This is the same situation as cold glass on windows having water droplets inside your house during the cold winter months.
The condensation occurs on your concrete floor when warm air from a relatively warm day comes into contact with the cold concrete. The cold concrete is caused by the colder winter months cooling the soil under your concrete floor, much like the walls of a cave.
Like the walls of a cave the water vapor condenses out of the warm air and turns into water droplets when it touches the cold stone, cave walls. Your concrete garage floor is like the cave wall, cold and moist. When the temperature drops and the humidity rises, the dew point is reached. The dew point is the point where the water vapor no longer remains in vapor, gaseous form but instead condenses back into water droplets.
This is condensation that you describe and by definition…condensation is moisture “condensing” out of the air into water droplets when the moist air inside your garage “touches” the cold concrete floor. This condition often occurs in garages where, during spring time, the floor remains cool. The warm, moist spring time air flows into the garage and the warmer, moist air condenses into a “wet floor” on a warm and comfy day.
There is no coating, paint or insulation that avoids this. Heating your garage concrete floor with a radiant heat system through the cold winter months will avoid this condensation problem on the few days that conditions are right. This is just the law of physics manifesting itself on your garage floor and is very common in St. Louis. I hope this helps you understand your wet garage floor.