We’ve gone through a period of very high heat and humidity locally, and I’ve noticed what looks like wet patches on our basement concrete floor, but they’re not wet to the touch. My first thought was that the washing machine had developed a leak, but as the temperature and humidity has dropped, the damp patches have disappeared. Could it just be the effect of the humidity?
The higher temperatures outside mean that the air can hold more water, so the high humidity at higher temperatures means that there is a lot more water in the air. The basement floor is cooler, which is why the water condensed out of the air.
so it’s not something I need to worry about?
Well, water outside of sinks, tubs, and pots in the house is never a good thing. Get a dehumidifier.
It could lead to mold forming and prevent you from installing a floor covering. There are tests that are relatively inexpensive and can be DIY. If the moisture level in the slab is too high, there are a number of remedies, including paint type products, some being more effective than others. You’ll need to do some research if you need to learn more.
Slabs, especially in a basement, can take several months to completely cure, i.e: dry to acceptable levels for covering.
As was suggested, a dehumidifier can control condensation due to periods of high humidity and prevent other problems.
My basement does the same thing. In addition to the dehumidifier, I put a big floor fan in my basement, to keep the air circulating. I’m hoping that will prevent any localized high humidity levels from causing mold or rust. I had a problem when I stacked up some beadboard style plywood panels, humidity got in, and didn’t get out, so they developed mold.
I leave the fan on almost all the time, and turn on the dehumidifier when the humidity levels go up. You can also get a hygrometer and monitor the humidity down there.
Of course they weep. The life of a basement is a thing of continuous, indescribable sorrow. I’d weep, too, if I were a basement.
Moisture always seeks to equilibrate. If your basement is less humid than the surrounding soil, moisture will move through the permeable walls and/or floor. Preventing this from happening has to be done at time of construction, or later on at a significantly higher cost.
Mine does during heavy rains or snow melt. It was poured 42 years ago and seems to be doing okay.