Cause: Slabs
If the room in which you are using your chair mat is built on a slab foundation, you may find significant amounts of water accumulating on the underside of your chair mat. As moisture is released from the concrete slab, it passes up through the carpeting and, usually, evaporates into the air. In areas where there is an impermeable barrier, such as a chair mat, the moisture will become trapped and condense. Concrete is continuously absorbing and releasing moisture, so the solution to your condensation issue lies with your chair mat.
Cause: High Humidity
Humidity is a measurement of the evaporated water in the air. Humidity can make otherwise comfortable temperatures feel muggy and close. Additionally, it can cause condensation and moisture issues in your carpeting, especially under a chair mat. Humid air becomes trapped between your chair mat and the carpeting and, as the chair mat is below the indoor dew point, the water condenses on the underside of the mat.
Solution: Ventilated Chair Mats
Many chair mat manufacturers have designed mats with the specific intention of encouraging air flow and reducing the likelihood of moisture problems. These chair mats are manufactured with small feet or teeth that keep the mat slightly up off the floor or carpet. Additionally, they have small ventilation holes that allow air to circulate under the mat, reducing the places where moisture can be trapped. These mats can go a long way toward eliminating moisture issues.
Solution: Reduce Indoor Humidity
Many modern air conditioners have a thermostat that allows homeowners to set the desired humidity level for their home. When the humidity percentage rises above the setting on the thermostat, the air conditioner cycles on and dehumidifies the air. Alternatively, simply turning on the air conditioner or running a dehumidifier will work to reduce the indoor humidity. Reducing the indoor humidity will not only improve the comfort level of your home, but will help reduce the amount of moisture in the air and the amount of moisture available to become trapped under your chair mat.