My house is on a slab and has an attached carport. The concrete in the carport gets covered with a film of moisture whenever it rains. The rest of the driveway will dry out but the area under the carport stays wet. The entire surface gets a film of moisture, even 12 feet from the open edge where rain can’t reach. Eventually, I want to enclose the carport to make an extra room but am worried about this moisture problem. Any suggestions?
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In the spring of the year the concrete block that is your garage floor is the temperature of the cold soil mass from the winter's deepfreeze. As a warm moist front moves in to bring rain it also raises the humidity and your garage floor is a giant cold object that is at or below the dewpoint for that humidity. And it "sweats" the same as that cold glass of iced tea "sweats" in the simmer.
Keep the garage door closed to help moderate the influx of humidity and to raise the slab temperature by allowing the house's warmth to migrate into the slab.............OR
heat the garage....................$$$$$$$$$$$$$$$$$$$$
.............................Iron Helix
Iron Helix is on the right track, even if he missed the part about a carport instead of a garage. As long as there is no standing water or puddles, and the moisture evaporates soon after the rain has ended, you should be in good shape. ...that's not a mistake, it's rustic
When you get ready to enclose the carport you will need to seal the concrete BEFORE you start building the walls and the interior.
There are lots of good sealers available. Talk to a concrete specialist in your area to see what works best in your part of the country.
I sealed my garage floor with a product called "Master Shield" about 10 or 12 years ago, and it has held up well. This product is/was a commercial type product, and I don't know if it is still available or not, but many products just like it are available everywhere nowadays.
The sides of my slab still get damp, so I know the moisture is still there during very humid days, but the sealant keeps the moisture from migrating to the surface. This is a MUST if you plan on installing any kind of flooring in the carport conversion later.
Just a thought...James DuHamel
J & M Home Maintenance Service
"Southeast Texas"
This is helping, thanks. But I wanted to point out that we don't have deep freezes (I'm in central Texas) and don't know if that makes a difference in the advice I'm getting. Also, the moisture film stays put for a long time, even after all the other concrete surfaces have dried out. I'm wondering whether some kind of sealant was used in the carport... the texture seems smoother than the driveway and sidewalk.
It's possible that a hardener was placed on the setting concrete. I have seen this in industrial applications and it makes the concrete surface very smooth. Also, in a warm climate, the slab is acting like a cooling blanket and holding onto the moisture. When you want to enclose the space. a wash with diluted muriatic acid and then a sealer as proposed should be good....that's not a mistake, it's rustic
Thank you for the words of wisdom. I'll give that a try.