The Importance Of Dew Point And Concrete Floor Coating

As contractors we like to work. Once you are working on a project you become eager to see it through completion. There are times that it is best to call it a day and come back on another day to finish. Humidity in the air can be one of those reasons you do. In this article we discuss humidity and dew point and what they mean to you installing a polymer floor coating.

Dew Point Explained

Humidity in the air can put a stop to your next floor coating project. You should always be aware of the conditions of the day so you can make the right call. This bring us to Dew Point which equals the temperature at which condensation begins to form, depending upon the amount of moisture (humidity) in the immediate, surrounding atmosphere. Once dew point is equalled condensation starts to form and it will do so on a surfaces with concrete being one of them.

The general rule of thumb

Never Install any kind of floor coating when the Dew Point is within 5 degrees (3 celcius) of the temperature.

Breaking Down Dew Point

The three factors that are used to determine dew point are as follows:

  • Ambient Temps
  • Ambient Relative Humidity
  • Concrete Surface Temps

The air holds water like a balloon. On any given hot day it will hold more, but it can only hold so much before it reaches full saturation and it pops. Since dew point equals the temperature to which air must be cooled in order to reach saturation it only makes sense that its a risk to install on day where DP is within 5 degrees of the ambient temps.

What moisture does is it affects the way the coating crosslinks. At best It may take it longer to cure or you might get mild blushing. Or worse case it may cause major blushing or adhesion issues.

Tools That Can Aid You

You really don’t need much. Since most people already own smartphone there is more than likely at least one person on the crew that has one. Any given weather app will quickly tell you the dew point however, on the app, you will want to specify the exact town you are currently in each time so you can get more precise location specific weather. Here you see a screenshot of my Weather Channel app on my smart phone. You can see that Dew Point is displayed below and the temps are displayed above. 

However, you could go out and get a digital thermometer that easily displays two of the three factor explained above (ambient temps, ambient relative humidity). The benefit of this over the weather app is 2 fold. Number 1, You won’t get epoxy all over your phone and Number 2, you will always have temps and DP at a glance. Just pop your head up and you know. You also want to purchase a handheld surface thermometer to achieve the final factor (surface temps).


Here is a good example. If the ambient air temperature is 70°F and the dew point is 57°F (which is a relative humidity is 65% in case you were wondering, geek). No coating should be applied unless the surface temperature of the concrete slab is 62°F or above. If the concrete surface temps reach below the 62°F threshold you are at risk the problems we described above.  


Don’t worry its very simple. You are basically comparing two numbers, concrete surface temps versus dew point. If they fall within 5 degrees, DON’T DO IT. Sure you will also be looking at the forecast for rain as well and you know it’s gonna rain the outside temperature get closer to meeting the dew point temperature.

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