Condensation on garage floor

[fairlaniac]

I had a new garage built last summer, 28x24x10. I epoxy coated the floor a few months later. I keep 2 cars in there with tools and other car guy ****. On the side of my '64 Comet which is the side most directly in sunlight the floor is dry. On the side of my '66 Fairlane the floor under the car is damp? The garage is in the open, no shadows cast upon it. I did a temp scan on the floor surface and the dry side was 72.7 and the damp side 71.6. Not much difference. The garage is built up. I had shale brought in when I built the pad and the gutters take the rain way past the garage and the driveway leading in is loped away from the garage. any ideas? I don't want the moisture trapped under the Fairlane and causing rust.

Thanks,

 

[pattenp]

Humidity and lack of air flow in areas can cause the floor to stay wet. Add a fan to keep the air moving in the garage.

 

[Firebird 1]

Did you put a plastic vapor barrier under the concrete before the pour?

 

[pattenp]

Did you put a plastic vapor barrier under the concrete before the pour?

If you're thinking moisture from under the concrete coming up, that should not be the source of the moisture since the floor is epoxy sealed. It should be just condensation.

 

[buddyboy]

it's more than likely condensation.

warm moist air will condense on surfaces at the dew point.

it's too late now to insulate the slab, use fans to keep the air moving.

in the summer when your slab is a cool 75 and you open the doors to +85 degree +80% humidity air you might have the same thing happen.

 

[fairlaniac]

Humidity is probably the culprit. I'll experiment by checking the floor today and open the doors, it's pretty humid here today. Should happen quickly.

Thanks,

 

[toolmiser]

Years ago my parents had a finished garage that the floors sweat like crazy. They found by leaving the attic hatch open (with a screen) that it kept it very dry. Might be worth a try.

 

[wssix99]

I did a temp scan on the floor surface and the dry side was 72.7 and the damp side 71.6.

If the dew point was above above 71.6, then that could cause condensation on the epoxy (cold slab) from the warm, humid air. You can calculate the dew point here if you know the temp and humidity at the time: http://www.dpcalc.org/

The same thing happened to me in Chicago this weekend. The epoxy was pretty slippery. I'm really glad I went with a textured flake, now!

The epoxy should protect you from any moisture coming up through the slab. If you just had condensation on the slab, that shouldn't be anything to worry about and you probably won't notice it again until we get really hot/humid weather after a period of cold.

 

[58Yeoman]

I have a 24x40 finished pole building, with 3 ceiling fans running on high. I was getting condensation on the floor, so I put a dehumidifier in there, and it's really dried it up. On humid days, I can work in there and be comfy with the doors closed (so far this year).

 

[Highbeam]

When conditions are just right, the car itself can form condensation. It is especially bad on the big, heavy, castings like a cold engine block.

 

[wantacoe]

I had my garage for 10 years with no problems. Then I decided to epoxy the floor. The next spring I got condensation on the floor. Mine only happens in the Spring and once in a while when it is very humid. With that paint on there it is like walking on ice!

 

[whiteg77]

Assuming your epoxy is bonded to the floor well enough, try taping a piece of clear plastic down to the floor and watching it for a few days as you go about your business, if moisture appears underneath, suspect that the cement may be wicking it up. If it appears on the top, exposed side, suspect condensation.

I don't have vapor barrier under my slab (don't ask why please lol), it's three years old, 4 inches thick and sits on a 6 inch to 12 inch bed of slag. This time of year, I'll see condensation on my floor once in a while, but then it clears. I also noticed that when it's happening, any parts of the floor that are covered stay dry when uncovered (ex - moving my winter tires around while cleaning up.)

Good luck

 

[ryan77]

would one say if the underside was insulated, this would be eliminated in all conditions? or is vapor barrier enough, the underfloor insulation is expensive.

 

[buddyboy]

if you insulate under the slab, then it will be easier for the slab to adjust to the temp of the garage.

the ground is an almost infinite heat sink, with no thermal break your slab will take a few more weeks in the spring to warm up and a few more weeks in the fall to cool down.

 

[6768rogues]

I get a little condensation this time of year when the floor is cool and a hot humid day comes along. Then the floor dries up for the remainder of the summer. I run ceiling fans and they nearly eliminate it.