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My garage slab has no vapor barrier and I live in Houston which is often wet and almost invariably humid. Water seeps up through the concrete and humidity is always pretty high in the garage. Power tools don't care much but my chisels and hand planes are a red mess after a few months which requires very deep and cumbersome cleaning. Is my only option to install a vapor barrier and add on 3 or more inches of concrete on top? Would it be possible to wait for a long dry spell and apply some kind of sealant or will this just peel off as the water moves up?

  • I think that'll depend on the ground under the concrete. If it's as damp as the air, paint will just peel. Do you know how deep your water table is? – Robin Bennett Dec 23 '19 at 13:35
  • What about a dehumidifier in the garage? Maybe a cabinet in the house for just your chisels and hand planes. – JACK Dec 23 '19 at 13:43
  • Are you sure it's not condensation from the air? In the spring when the ground is sill cool my slab sweats like a rock drummer. It's not from the ground. The only solution then is to dehumidify the air. I suggest absorbent material in totes for tool storage rather than fighting nature throughout the garage. – isherwood Dec 23 '19 at 14:06
  • Dehumidifier in a sealed cabinet (or closet) for the tools. Costs less to run than getting the whole garage dry... – Ecnerwal Dec 23 '19 at 14:38
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I have had great luck at sealing slabs with 2 part epoxy paint, in a garage you don’t want to go cheap or when you drive the car in and park it where the tires are ends up pealing up.

I have painted in summer when the slab was dry enough and eliminated a huge amount of moisture in basements. This will help if the source is from the slab if high humidity is from the air a dehumidifier will be needed. I had a friend use a single part epoxy paint and he had the pealing problem. We stripped the paint and used 2 part and it held up fine.

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I've used a product called Xypex. There's a lot of these Integral Crystalline Systems on the market. The manufacturers say that the thin slurry penetrates wet concrete, especially new concrete, forming dendritic crystals that grow into and fill the microscopic pores and cracks. They claim that the crystal growth penetrates concrete several inches deep. These products are used to seal public concrete water tanks, tunnels, underwater bridge supports, etc. These crystalline sealers are sold by masonry supply companies.

The product, unused, just resembles a very fine grained Portland cement powder. It is mixed with water to a slurry. The idea for application is to thoroughly soak the concrete, then brush on the slurry. As the concrete drys the crystals grow into it, sealing it up. Xypex leaves a finish reminiscent of kiln fired ceramic glazing. I've used it to seal concrete basement/foundation walls, with good results. The basements stay dry.

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