How to avoid "sweating slab" in the warehouse

If your warehouse or DC routinely develops a wet spot that's so deep employees refer to it as "the lake" and give it a name, then you have a bad case of "sweating slab." That's a real but extreme example of a phenomenon that causes cement floors to become wet and slippery, creating hazards for pedestrians and lift truck operators.

Slab sweat can happen when a thick expanse of concrete is in direct contact with the ground, explains Christian Taber, senior applications engineer for Big Ass Fans, a manufacturer of industrial fans. Because it has a large thermal mass, the slab takes a long time to heat up, and a lot of heat is required to change its temperature. As a result, the floor temperature tends to trail the air temperature by about a month. In April, for example, "the air may be warm and humid, but the slab is still back in March," he says.

Another cause of slab sweat is condensation that forms on the floor when the slab temperature is lower than the dew-point temperature of the air. "This happens a lot in unconditioned space, especially facilities that aren't heated well and those that aren't air conditioned," Taber says.

It's a problem to be taken seriously. The combination of forklifts and a wet floor can lead to tipping or sliding, potentially causing harm to people, trucks, racks, and product. Wood pallets and cardboard cartons that come in contact with slab sweat provide an environment for fungus, mold, and mildew—"the odds of something growing are pretty good," Taber says—not to mention the danger of cardboard boxes falling apart or metal products rusting.

How can you prevent wet floors? Air conditioning removes moisture from the air and lowers the dew point, but it can be expensive to install and operate, Taber notes. Another method is to raise the surface temperature of the floor by using a radiant heater or blowing hot air directly on the problem area so it gets above the dew point—a "fairly energy-intensive solution," he says. A third option is using overhead fans to blow the warmer air near the ceiling down onto the slab. Fans also keep the air moving, making air temperatures more consistent throughout the facility and reducing the difference between the dew point of the air and the floor temperature.