One of the most common questions we hear at Progressive Materials is “How much coating will I need?” Many factors go into answering this accurately, and the results will vary each time. The amount of coating needed, however, is always measured in “mils.” To those unfamiliar with the process, you may be asking, “What’s a mil, and how do you measure it?” This blog will explain mil gauges and how to use them.
What’s a Mil?
A mil is a unit of length equal to one thousandth of an inch. It’s a common unit for specifying thickness of roof coatings, plastic film, paper, and other products. It’s difficult for many people to visualize such a small dimension. To give a point of reference, most plastic credit cards are about 30 mils thick. It’s also important to remember that the term “mil” isn’t an abbreviation but an actual unit of measure.
Use in Coatings Industry
Like many other manufacturers, PM requires its coatings to be applied to certain mil thicknesses for warranties on roof applications. A 5-year warranty, for example, requires 15 to 30 dry mils, depending on the substrate. A 20-year warranty requires 30 to 45 dry mils, again depending on the substrate. Our Silicone Coverage Guide details the mil requirements for PM warranties.
But how do you measure coating? That’s where a mil gauge comes into play.
Using a Mil Gauge
While some mil gauges are digital and battery-powered, this blog will focus on the more common wet film thickness gauge comb.
The instructions for using this type of mil gauge are straightforward:
- Hold gauge perpendicular to surface and place it into fresh, wet coating. Do not press down on the mil gauge; just let it sit in the fresh coating.
- Remove gauge from coating.
- The wet film thickness lies between the last tooth with coating on it and the first tooth without coating on it.
- The wet film thickness multiplied by the volume solids of the coating material will provide the dry mil thickness.
Here is an example of computing wet mils into dry mils: If the wet film thickness is 30 mils and you are using PM’s HS 3200 Series, you would multiply 30 by 92 percent (0.92). That will tell you that the dry mil thickness will be 27.6.
In our mil gauge tutorial video, PM Technical and Educator Coordinator Jeff Romero walks through the ins and outs of mil gauge usage. You can find that video here.
Conclusion
PM offers great warranties for up to 20 years, and mil thickness is a major factor in determining the warranty period. A mil gauge, when used properly, can help maintain consistency in silicone applications.
Reach out to your local Regional Manager here if you need mil gauges or have any questions.
Thanks for reading.
