Moisture under garage mats

[Jacobn]

Here's my situation: I have an approximately 400sqft detached garage that I converted to a gym/workshop. Spray foam insulation on walls and under roof deck (no false ceiling, open to the rafters). It's built on a slope, south wall is about 4 feet below grade, north wall is the garage door that is on grade (garage door is insulated with foam panels). I don't have any moisture coming through the below grade parts of the walls. The floor is a concrete slab that's pretty beat up, with cracks and smallish depressions of broken concrete here and there. I was in a rush when I was finishing it and just threw down 3/4" thick rubber mats from Tractor Supply (with coin-sized dimples on the underside to conceivably allow airflow). Garage also has a mini split and ceiling fan for heating/cooling and air flow.

My problem: I now have a fair bit of moisture build up under the rubber mats and what appears to be mildew (hopefully not mold?). What's the best way to deal with this? I'm considering trying to get a bit more insulation on the floor, something like dricore subfloor panels (not the OSB ones, the purple ones) to put under the rubber mats. I'm assuming the moisture is coming up through the concrete though. Should I fill all the cracks/pits and seal first? What should I seal it with? Money is an option, don't want to spend an arm and a leg to fix this, and plan to DIY it, but also don't think it's a good idea to let this fester for a long time. I have no idea if there is a vapor barrier under the slab.

I live in Spokane, WA, fairly cold/wettish winters, dry/hot summers. Thoughts?

 

[The Cobbler]

nothing you put on top will stop the moisture from coming up from below .

 

[billconner]

nothing you put on top will stop the moisture from coming up from below .

Well, a vapor barrier and 3" of concrete maybe. Depends on door sills and such.

 

[BillK]

My problem: I now have a fair bit of moisture build up under the rubber mats and what appears to be mildew (hopefully not mold?).

I live in Spokane, WA, fairly cold/wettish winters, dry/hot summers. Thoughts?

Its condensation because of the cold garage floor. I dont think there is much you can do about it. I have one mat in front of one of my work benches that is actually an old piece of conveyor belt and has a rough "dimpled" finish on the bottom. That is the only one that does not get moisture build up.

 

[kngelv]

RaceDeck underneath the mats will let the moisture sit between the top of the tile and the floor. As long as you have a gap at the edges then the moisture will have a path to escape.

James

 

[Treeman]

As the previous different answers allude, you need to determine if it is moisture from below or condensation from above. This time of year in Michigan, the very cold concrete can condense moisture on humid days. I have dry concrete garage floors but underneath some mats it will be wet. I think this is moist air vapor making its way under the mat, then condensing on the concrete because the mat insulates that area, keeping it colder compared to surrounding areas. I don't see moisture under those mats any other time of year.