By Tanzin Fatima
Building designers across the U.S. would agree that it is crucial to select an appropriate weather (air, vapor, and water) resistant barrier in accordance to the standard code, to prevent water infiltration, and to control air leakage in a building envelope. There are three main types of WRB membranes that are commonly used: self-adhered, fluid applied, and mechanically fastened. In regard to fluid applied vapor permeability, there are two types of WRB: vapor permeable and non-permeable. This article will discuss fluid applied VP and NP membranes in thin and thick mil applications and highlight the advantages thin mil applications have over its thicker counterpart.
In manufacturing, mil thickness is a common measurement unit to describe the thickness of materials in thousands of an inch (1 mil = 0.001 inch). Thin mil systems generally refer to mil thickness of approximately 8 to 10 DFT (dry film thickness) and thick mil systems are approximately 40 to 70 DFT. Thickness and chemistry of coating formulations may affect many properties of installed systems, including air barrier assembly procedures, water leakage, weatherability, longevity, and durability.
The Fluid Applied Air Barrier, a Canadian-developed technology, originally required heavy bodied products with thick mil applications. Thin mil systems were invented approximately 18 years later out of the EIFS industry (Wolff, 2016).
Building designers/contractors have had a major long-standingdilemma about choosing the right mil thickness for their projects. Certainmanufactures in the industry frown upon thin mil systems and heavily promotethe more traditional thick mil systems. There is a common misconception thatthicker membranes would have advantages over thinner membranes. Granted, athicker mil should make the building envelop more durable, in theory.
However, in reality, membrane thickness is not the soleattribute to consider when selecting a WRB system, rather, ultimateperformance, longevity within the wall cavity, and application properties ofthe membrane should be taken into consideration. Despite a few advantagesassociated with a thick mil air barrier system, in most cases a thin mil WRB isa fine option, or even be a better choice to prevent air permeance into abuilding. Thin mil systems have following advantages:
There is often a false sense of security associated with thickmil WRB. For instance, some thick mil manufacturers fail to mention thatregardless of mil thickness, water will pass through an opening or a hole. Whenthere is a hole caused by a penetration, under extreme conditions leaks mayoccur regardless of the barrier thickness. If water finds a penetration, thereis no measurable difference if the penetration is through thin or thick milFAAB (GP, 2019). In addition, when either thin or thick mil coatings areapplied over a sheathing material, the joints should be sealed with otherhigh-quality sealants. As a result, moisture penetration is not determined bymil thickness.
PERFORMANCE CONSIDERATIONS:
APPLICATION CONSIDERATIONS:
In conclusion, fluid applied air barrier systems for building envelope technologies are expanding in use and ever growing. Based on the technologies/chemistries available today, it is understood that most coatings will perform based on the chemical, mechanical, and rheological properties of formulations, rather than based solely on thickness. Regardless of mil thickness, some coatings are superior performers than others due to the advanced technologies (i.e. STPU/STPE). Asphalts are highly flammable and present safety hazards as well as compatibility issues due to bleeding. Acrylics have low-crack bridging abilities at low temperatures, questionable durability, and inconsistent performance properties. Hybrid technologies (STPE/ STPU) have erased these problems by fusing best properties of silicone (weatherability and flexibility) and urethane (strength and durability) in one package.
Tanzin Fatima is a technical service representative and document editor at Pecora Corp. At Pecora, Tanzin writes white papers and technical literature; creates and revises technical product documentation; and builds relational databases to manage experimental data and automate reporting. She also conducts and monitors project testing of construction sealants, aid quality control and performs developmental product testing. In addition, Tanzin has conducted inspections of processes and infrastructure, updating operational drawings, and reviewing projects with management.