Roof Coatings DFT: Mil Thickness

Roof Coatings DFT: Mil Thickness

There are a ton of different types of roof coatings out on the market. The basic key to most of these roof coatings is the Dry Mil Thickness (DFT). Mil is a reference to thousandth of an inch thickness. One mil is one thousandth of an inch thick. To give you perspective, standard copy paper is about 8 mils thick. A standard credit card is anywhere form 20-30 mils thick.

DFT Guidelines

All manufacturers have guidelines on how thick their coating should be applied. Most often they are given in DFT. How they reach that thickness can vary greatly depending on how they are applied and the percentage of solids the particular material is. As a customer what you really want to know is what the DFT will be. This will give you a good idea as to how you should compare roof coating quotes between companies bidding on your project.

Quotes should include how thick the contractor is applying the coating and to what manufacturers specifications they are following. Our quotes state that we are installing the roof to the manufacture’s 10 year specifications. For instance, Gaco Western’s silicon roof coating is applied at 1.5 gallons of silicon roof coating per 100 square foot, which is approximately 22 DFT.  There are many other aspects that also matter when it comes to roof coating thickness.

Percentage of Solids by Volume

Roof coat thickness is only one aspect of roof coatings. The percentage of solids by volume or weight are also an important aspect. This means that if a coating has a 50% solids by volume, when you apply one gallon of coating about half of the coating cures off (leaving only half the material you applied). As an example again, Gaco Western’s silicon roof coating is 95% solids. 95% of the roof coating will still be there once it dries.

Fun fact: all liquids applied at one gallon per 100 square foot have a wet millage of 16 mils.

It is also important to consider how thick the coating can be applied in a single pass. Most acrylic roof coatings need to be applied in several passes. If you apply them too thick in a pass they will mud crack, leaving big cracks in the coating. Since polyurea roof coatings dry very quickly they can be applied in very thick passes, over 40-60 DFT.

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How is your contractor going to check and prove that he is applying the proper thickness? Using a wet mil gauge is the most common way, but you can also use a coating thickness gauge.

When it comes to roof coatings, don’t let someone sell you a quick paint job when you really need a roof coating. Call us today!