Condensation / damp from garage floor. Can it be fixed?
I've got a basic garage in the backyard - essentially a sheet metal shed with a concrete floor. It would have been built in the 1980s so I doubt the concrete slab had a water barrier - or if it did it probably wore away over time.
When we have wet weather, the concrete gets damp underneath items on the floor - like rubber mats etc. There's also some mineral staining. Doing some reading online, it looks like concrete efflorescence.
I'm considering demolishing the shed and building a better workshop (insulated etc.) on the existing concrete slab. Can I make the existing slab a usable floor by sealing it with something like epoxy? Or would I be better off using the slab as a footing and building the new structure on posts with a separate floor suspended above the slab?
My goal is to avoid getting any damp or mould in the new structure.
Thanks for the reply. Sounds like it isn't worth keeping the existing slab as flooring. I'll weigh up if it's worth demolishing or if there's merit to leaving it in place and building on posts over the top. I'm in Australia so the ground freezing isn't an issue but I don't want a situation where I could have mould under the floor.
Yeah you have no vapor barrier under that slab, I’d bet my money on that.
You can try sealing it in with various tricks but in Finland it’s considered a risky building structure to have a vapor barrier on top of the concrete - that’s a situation ripe for mold issues.
The issue is that capillary action forces water up through the concrete - if you seal the surface it’ll just collect underneath your make shift vapor barrier and eventually find a way around or through.
With a concrete slab on grade you need some way to stop this capillary action beneath the slab. I.e. layers of gravel in various sizes and a plastic vapor barrier.
My dad had a damp concrete floor basement (unfurnished) that he was using as storage and his solution is leaving a dehumidifier there basically 24/7, and occasionally emptying the water container. As far as I could tell, it wasn't too bad.
Sealing the floor definitely reduces condensation and would help with your problem, but personally I am not experienced enough about how you'd go about doing that.