Measuring mil thickness during fluid applied air barrier installation

Installers know that once fluid applied air barrier installation is complete and the material has fully cured, the design team needs confirmation that the membrane measures to the dry film thickness suggested by the manufacturer.

For many years, fluid-applied membranes have been specified in commercial construction to perform in wall assemblies as air barriers, vapor barriers and water resistive barriers. These products are typically used over exterior sheathing or concrete block. They are often used in place of mechanically-attached sheet products, as fluid-applied systems provide the following advantages:

  • Improved air and water tightness
  • Full adhesion to the substrate
  • Monolithic installation
  • Sealing around brick ties and fasteners

Fluid-applied membrane products on the market are of diverse chemistries. Their manufacturers also specify installation at many different mil thicknesses. The mil thickness affects many properties of the installed system, including:

  • Effective substrate coverage
  • Continuity of the air barrier assembly
  • Seal around brick ties and fasteners
  • Bridging of cracks
  • Integration with flashing details
  • Coverage of caulked joints and terminations

Specifiers of roofing systems and traffic coatings would not consider classifying systems of significantly different thickness as equals. Yet fluid-applied membrane air barriers, whose specified mil thickness varies between 7 mils and 120 mils, are often placed in the same specification and classified as “equal”. In spite of the emergence of thin mil systems, the most common specified dry film thickness of fluid-applied membrane products is 40 mils. This matches the thickness of self-adhering roofing underlayments and self-adhering air/vapor barrier membranes, both of which have a very good track record of providing effective waterproofing in their respective applications.

How to measure the dry film thickness of a fluid applied air barrier
How do installers accurately measure the dry film thickness of a fluid applied air barrier? That’s a question our tech services team gets asked often. The answer begins with a distinction between types of gauges.

A wet-film gauge cannot be used to determine dry film thickness of air barriers. The wet film gauge should only be used while installing the air barrier to confirm the wet film thickness. Cutting out a piece of the membrane and trying to measure the dry film thickness after the air barrier has fully cured out is very inaccurate.

One of the most reliable ways to measure dry-film thickness of an air barrier is to use a digital dry film gauge. There are many different manufacturers of these gauges and they are typically very accurate.

A dry film gauge is fairly expensive, but makes verifying the dry film thickness of air barriers easy, efficient, and quickly resolves any questions regarding the installation. Investing in one will pay for itself in no time.

If you need additional support around measuring mil thickness during fluid applied air barrier installation, Henry Company can help. Schedule a meeting with one of our expert advisers today!

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