Sweaty Concrete?

[Brad Schafer]

Not the right time of year to post this, but what the heck ...

My shop/garage is 24x30 with a slab floor (no interior drain). The only heat in there is a smallish Ouellete box electric heater to provide some spot relief during really cold spells.

I have terrible trouble with moisture in the spring when the temp turns; the floor sweats like mad and about the only thing I've been able to do to avoid it is to leave the thing closed. :mad: The wet floor is aggravating enough, but even more annoying is the rust factor for the big machines in there (e.g., tablesaw, shaper).

Any suggestions on how to mitigate this, apart from putting in a woodburner and heating the place (and therefore the slab) regularly?

Also, what's a good way to keep machine tops from rusting other than a good buffing with wax (which I've tried in the past, with marginal results)?

Maybe if I can figure this out now, I can avoid the war that's sure to come next spring. TIA,

-b

[Jason Roehl]

Brad! Good to see you on here!

Open it up as soon as it starts to warm up to get that concrete up to temp. Run fans to circulate the air and prevent condensation from forming. Run a dehumidifier when it's closed. Cover machinery with canvas tarps (breathable).

Short of conditioning the space full time, that's about all you can do.

[David Gutierrez]

Sounds like the cold slab has warm moist air hitting it and condensing out. You might want to try a dehumidifier...

[Brad Schafer]

Hey J - hope you're well.

I concur with Dave G - it's definitely condensation, but I've never seen anyplace else sweat this badly. A dehumidifier doesn't touch it ... the last time it happened, I squeegeed a gob of water out - probably close to a 5 gallon bucketful - and then started multiple box fans going. Didn't help much. I wonder if it's due to the epoxy floor paint I put down a few years ago, since I don't remember it being this bad except in the recent past. Of course, with the temp swings here in the Midwest spring, maybe I just need to be more observant.

Phooey.

[Randy Reitz]

Is the slab below grade? If you're getting 5 gallons of water from a 24'x 30' slab it may be a seasonal water table above the level of the slab surface. This especially can happen in the spring. If so you need external drains below the slab level. You also need to double check surface run-off from the roof and surrounding area.

[Brad Schafer]

nope - well above grade (min 6" level diff from slab to ground level), and there is a well-done footer drain surrounding the thing (did it myself ;) ). but you do make a good point; i'll check again to see if there's any excess moisture anywhere (if we ever get any rain).

great quote BTW.