Can Concrete Floors and Walls sweat? (Video)

“Greg Batista here once again to answer your online questions.

Bubblwatson asks: Why does my concrete garage floor look like it’s sweating?

That “sweat” is really condensation. Concrete surfaces get cooler than the surrounding humid air, especially in garages or shaded walls. When warm, moisture-rich Florida air hits that cooler surface, water vapor condenses, just like a cold soda can on a hot day. The U.S. Department of Energy notes that Florida has average relative humidity above 70% most of the year, making condensation a year-round problem.

This isn’t just annoying. Over time, moisture seeps into the slab, fuels mold growth, and accelerates rebar corrosion inside the concrete. Engineers often recommend coatings, dehumidifiers, or better ventilation to reduce the risk. Left untreated, what looks like simple “sweat” can shorten the lifespan of your structure.

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Authoritative references: U.S. Department of Energy – Moisture Control Guidance for Building Design; ASHRAE Humidity Design Standards.

The author, Greg Batista, PE, CGC, SI is owner of G. Batista Engineering & Construction and is a nationally-recognized engineer and contractor with more than 35 years of experience and offices in Fort Lauderdale, Florida.