What is Dew Point and How Does It Affect Floor Coatings?

Dew is the condensation of moisture you see on grass in the morning, on a bottle that was taken from a cooler or refrigerator on a warmer day, or the fog on the bathroom mirror after a shower.

As you’ll recall from school science classes, the dew point is the temperature to which air must be cooled to become saturated with water vapor. Once the air is saturated and can no longer absorb or hold water, the excess begins to condensate on available surfaces.

The warmer the air, the more moisture it can hold. This is why dew on grass generally dries up over the course of the morning, as the sun comes out and the day warms up. In other words, the dew evaporates, or gets reabsorbed as vapor into the surrounding air.

The term “relative humidity” (RH) is used to describe what percentage of water vapor is in the air, compared to how much it could hold at a given temperature. For example, an RH of 50% means the air is holding one half of the water vapor it is capable of holding at a specific ambient temperature.

The dew point depends on a combination of three things:

• The ambient temperature
• The ambient relative humidity
• The temperature of the surface

How to Measure Dew Point

There are many dew point meters available. However, if you have an instrument that accurately measures temperature and humidity, you can use a standard table that indicates dew point.

Here are several examples from such a table:

• If the temperature is 65 degrees Fahrenheit and the relative humidity is 50%, the dew point—or point at which condensation will form on objects—is 45 degrees Fahrenheit.
• What would be the dew point temperature, if we now had air temperature of 85 degrees Fahrenheit and relative humidity of only 25%? The tables tell us that the moisture vapor would begin to condensate if air temperature were to go down to 45 degrees Fahrenheit.
• At 100% relative humidity, the dew point is equal to the temperature. This is because a relative humidity of 100% indicates that the air is completely saturated with moisture, and there is nowhere into which the moisture can evaporate. In such cases, it is likely to feel extremely damp, with heavy fog and/or rain.

How the Dew Point Relates to Concrete Slabs and Finishes

Because of its porous nature, concrete has a tendency to absorb moisture. The typical recommended curing process for green concrete is 28 days, and that is the minimum waiting period before most finishes should be applied (with a few exceptions).

However, if the temperature of the concrete is below the dew point of the room, condensation will form on the concrete. This can play havoc with virtually any finish, causing:

• Poor bonding or adhesion
• Bubbling or cracking
• Fisheyes and craters

The rule of thumb is this: Do not apply a polymer floor coating when the dew point is within 5 degrees Fahrenheit (3 degrees Celsius) of the air temperature in the room.

Multi-colored industrial floor installed with an eye for detail by Florock UK of Great Britain.

A Note of Caution about Measuring Concrete Surface Temperature

Concrete’s surface temperature can be a bit tricky to assess. If the room is not fully climate controlled around the clock, the surface temperature may vary across different areas of the floor, at different times of the day. This is especially true in warehouses where doors, windows and vents are constantly being opened and closed. Areas closest to these openings can have wide shifts in temperature, even while the temperature in central aisles remains fairly stable. The same variability could be seen on loading docks, as the ambient temperature on the dock itself will shift as weather changes outdoors.

Another aspect to consider is this: Condensation most often happens as warm, humid air diffuses throughout the structure. When this occurs, it takes far less time for the interior air to change temperature than it does for the slab to adjust. Thus the slab can remain much cooler for longer, relative to indoor air.

It is important to closely monitor changes in dew point, as well as surface temperature, before applying a finish to a concrete slab.

Potential Safety Issues of Which to Be Aware

While it may seem that condensation would easy to identify, moisture on a floor is not always evident. This opens the door to potential problems:

• Slip-and-fall hazards for pedestrians
• Damage to goods left on warehouse floors
• Lack of traction for vehicles, such as forklifts

A facility prone to condensation on its floors can benefit greatly from slip-resistant floor coatings, which is customizable to each space, as needed.

Call Us for a Consultation

Florock offers a very broad range of flooring products and systems to meet virtually any commercial or industrial need. Our experts can help you evaluate your facility and recommend the flooring options that will best meet your requirements and budget. Try us today.