Garage floor damp

Question

Been reading on line for several hours now. I have dampness on my garage floor, note: it's about 8yrs old. If I put a box any where on the garage floor for several hours, there will be a damp foot print of the box underneath it. If I remove the box it will dry up after several hours but the edges are still visible. At first I thought I had 'hydrostatic pressure' causing the wet garage floor but I'm not below grade and the moisture doesn't appear to be coming up the cracks (minor). Then I thought maybe the underground drains for the rain gutters were the problem (they run on two sides of the garage) but they appear to be intact & functioning property, moving the water to the drainage ditch. To be sure I'm removed the gutter down spots from the drain lines. So now I'm reading about condensation, …. not really sure about this because here in coastal Oregon the temps are pretty constant. Also there no appliances in the garage. I also read about the lack of a 'vapor barrier'. So how would you test the "condensation' theory? and 'vapor barrier'? Or does anyone have some other thoughts? any and all help appreciated. I have considered installing a room heater in the garage but would have to do a lot of electrical work. GTB

EDIT: Thanks for the replies, Garage is above grade with no standing water near me. Actually I'm a foot or more above my neighbors and at least 4 ft about the drainage ditch. I going to dig a pot hole on the east side and check the soil, then I'm going to drill a hole and see if there is water under the floor, I don't believe there is but need to know for sure before proceeding to seal the surface.

Answer 1

Cement is an extremely porous material and if left exposed to water, will absorb water. As a side note, I have a cement pizza oven that will sweat many gallons of water when I add a fire.

You may have a high water table, pooling subterranean water, excessively damp soil or an underground pipe leak. Had you known, it would have been prudent to lay a groundsheet before casting the cement - something that is not done very often.

What can you do: well the best course of action would be try to minimise the water exposure or seal the cement. If you can gain access to the boundary walls of the room, you could dig a small trench and test the soil dampness (choose the higest point and dig to a level below the lowest point). If you find lots of dampness, one course of action could be to dig a trench around the entire structure and put damp-proofing sheets against the trench-walls.. that would help quite a bit.. unfortunately, that would be lots of work.

The other option would be to try and seal the floor with some cement sealer, just paint the cement surface with a floor or tile sealer and it should help with water permeation.

Answer 2

You may have the same problem that my son does, so let me explain. We live north of Pittsburgh, Pa, and for some reason that he and I can not figure out, his garage floor is extremely cold and the humidity in the garage will cause the concrete floor to swet a lot. The fix was to install a portable de-humidifier and run it during the warmer months. We drilled holes into the concrete believing that the problem was cold ground water but under the floor was dry. The humidifier did the trick and the floor stays dry now.