We've been in our house a little over a year. This spring a damp spot appeared (it wasn't there before) in the concrete floor of our under-house garage. And it hasn't gone away. We have no idea what's causing it and pondering it has left us baffled.

The spot is about 3 feet in diameter, off center in the garage floor. It's not near the walls or window. The floor is unpainted concrete and there are no pipes nearby. And most importantly, we don't even part our cars in there. It's more of a work space than anything and is mostly empty.

My first thought was a wet spring, some water crept in from below. That theory got scrapped when I moved a few items that were in the area and found that underneath the boxes and bags was bone dry, leaving nice outlines of the items in the midst of this damp spot. This said to me, it must be coming from above then. But the ceiling is dry and shows no signs of water, past or present.

My only other theory was that the window had been open (on the opposite side of the garage) and for some reason the morning air was condensing on the floor. Settling dew would explain the dryness under things, but why only that one area? I closed the window weeks ago. Yet the spot continues to mock us.

I'm out of ideas. I'm hoping the good folks here can offer me some explanation for this oddity and let me know if it's something to worry about or ignore as part of the house's "charm".

Thanks,

Rob

The Catholic Church still has exorcists, right? [just kidding]

Your logic seems unassailable. It's an interesting mystery.

You might want to figure out precisely what it is. The fact that it's not evaporating may mean that it's oily in nature. Figuring out what it is will go a long way toward figuring out where it came from.

Just a thought.

I do have a few items from Halloween in there. Maybe I made them a little too well. :D

If you spilled oil on the floor and left it there it is liable to break concrete up. You would have to cut out the whole and re lay concrete in the whole you cut out which is really easy and quick.

Nope, no spills. It just appeared one day of it's own volition.

I also have not yet rul ed out gremlins, sprites and pixies. Mischievous little buggers that they are.

Ha Ha Yes True But I Don't See Them Able To Break Into Or Be Under The Concrete, It Stumbles Me To Think What The Cause Of This Might Be, But Like I Said Repairing It Would Be Next To No Hassle At All.

Put two or three squares of paper towel (stacked/sandwiched atop one another) down on top of it, and then set a box full of something on top of that so it will put some pressure down onto it. Let it sit for 24 hours. Remove the box and look at the lowermost paper towel square. What soaked into it? Water? Oil? Mystery fluid?

Again, you're not going to get to the bottom of it until you figure out what it is.

I go along with your logic of condensation but I'd be more inclined to think that its warm humid air from the daytime being trapped in the garage at night when the doors are closed rather than night air entering through open window. The warm humid air being cooled at night by the garage floor could cause condensation. The question as you pointed out is why one particular spot. What could be under the garage floor that would make it cool enough to create condensation and why only one spot. You might set up a small fan in the garage at night to keep the air moving around to see what happens.

The house was built 43 years ago. This problem just occurred.

Was there a lot of rain right before this happened? If so I've seen where the water simply gets under a slab and that small spot had sunk enough for an actual under slab puddle to exist. Water could be coming under the driveway stone running in etc. Just because we see finial grade there are pockets/low spots for puddles to lay in the dark under drives concrete slabs.

There wasn't any rain. The substance looks and feels like oil, not water.

The Gulf oil leak got that far...

Sorry it popped into brain. Anyhow, is it possible that the garage didn't have a concrete floor back then and at time it may have been just stone or dirt. A long shot thought if someone was doing a lot of oil changes and letting it run into the ground, then created it later it could be wicking into the Crete. How long have you lived there? A previous owner could have had a bad oil leak in a power steering unit (clean oil) etc.

Is the spot where a cars rear or engine would sit?

I am hoping the garage is sitting on oil, then I could soon be rich... I have live here 14 years and this began to happen a few weeks ago. The oil slick is about 1 foot from the west wall of the garage in front of built in cabinents. No vehicle has been parked there since I moved in.

Another long shot. Are there any factories near you that use an oil substance? Lets bring it local, Do you know if there was an old heating oil tank buried at one time? Or one near that spot?