Ensuring proper air barrier adhesion for maximum performance

by arslan_ahmed | November 10, 2022 7:00 am

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By Iltaz Alam

With concerns about sustainability, energy use, and indoor air health on the rise, the performance of a building envelope has never been more scrutinized. Considering how air leakage often leads to increased heating and cooling costs, air barriers play a crucial role in reducing air leakage and protect against mold and other unhealthy conditions for occupants and structures alike.

Using a fully adhered air barrier, whether sheet-applied or fluid-applied, is essential in creating a continuous barrier which will minimize air leakage. How well the membrane is bonded to the wall substrate will greatly affect the barrier’s performance. This adhesion is a critically important, yet often overlooked, factor in air barrier selection, and it impacts the building envelope’s performance from the day it is installed and throughout the life of the building.

Small leaks, big impact

Even a small air leak in a wall structure can have significant negative effects. Heated or conditioned air can escape through the wall, increasing HVAC loads and energy costs, but what is even more concerning is the issue of moisture transport, called vapor drive.

Moisture vapor naturally moves from a high concentration to a lower concentration, until it is in balance. If the vapor pressure is high outside the wall and low inside the wall, vapor drive will be directed inward and vice versa. The greater the difference of this vapor pressure or “concentration gradient,” the greater the vapor drive. Temperature differential between the outside and inside air also affects vapor drive; the greater the differential, the more vigorous the vapor drive.

Consider this: The air passing through a 25.4 mm (1 in.) hole in a wall transports a hundred times more water than vapor diffusion through a 1.23 x 2.5 m (4 x 8 ft) gypsum wallboard, however, this is while assuming interior temperature is 21 C (70 F) with 40 percent relative humidity (RH).¹

When warm, moist air contacts cooler indoor air, it condenses and can accumulate in wall components, creating an ideal environment for mold growth. Moisture can saturate insulation, degrading its insulating properties, and can be absorbed by porous materials such as wood and gypsum, causing damage inside the wall which may not be visible. This makes the selection and proper installation of an appropriate air barrier pivotal.

Looking beyond codes

At a minimum, the barrier should conform to established industry standards. The Air Barrier Association of America (ABAA) has established
a maximum air leakage rate for wall air barrier assemblies at 0.2 L/s/m² (0.04 cfm/sf) at a pressure difference of 7.7 kg/m² (1.57 psf) or 0.075 kPa (75 Pa), when tested in accordance with ASTM E2357, Standard Test Method for Determining Air Leakage of Air Barrier Assemblies.² Another testing standard in use is ASTM E779, Standard Test Method for Determining Air Leakage Rate by Fan Pressurization.³ While ASTM E2357 is designed to be performed on a wall specimen in the lab, ASTM E779 is designed to measure air leakage of a built structure in the field, testing the envelope across a range of both positive and negative pressure differentials.

While measuring air leakage is important, it is not the whole story; the adhesive bonding of the air barrier to the wall substrate should also be assessed since it affects the long-term performance of a structure.

Adhesion is critical

The continuity of an air barrier and its ability to resist differences in air pressure are key physical properties to determine its performance. Strong adhesion of the membrane is needed to ensure a continuous barrier and one which resists pressure differentials.
To achieve this, the membrane must:

• Seal to the substrate, creating an aggressive bond across the entire surface.
• Seal to itself, preventing weak laps which allow air intrusion.
• Seal around penetrations, including fasteners, eliminating potential failure points.

Poor adhesion at any point can allow air to migrate behind the membrane and into or out of the structure. Further, the bond must be strong enough to withstand the test of time. Improper installation or a weak adhesive can result in a barrier which appears functional but may separate from the substrate over time, compromising the performance. Worse yet, with siding and other external wall components covering the barrier, building owners may not even be aware of the failure.

Given this risk, understanding the factors impacting air barrier adhesion are essential to make the right choice.

Testing adhesive performance

While manufacturers often have published specifications for adhesion strength, it is important to validate these claims independently. Fortunately, there are standardized test methods for measuring the pull-off strength of an adhered air barrier, including both sheet-applied and fluid-applied membranes.

ASTM D4541, Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers is designed to measure pull-off strength between an air barrier membrane and a substrate. It is used to assess in-field performance.⁴ The ABAA has a similar test method, ABAA T002-2019, Standard Test Method for Pull-Off Strength of Adhered Air and Water Resistive Barriers Using an Adhesion Tester.⁵ With both methods, a disc is adhered to the surface of the air barrier and allowed to cure. A test apparatus is attached to the disc and a pulling force is applied and gradually increased until failure. The pressure at failure is recorded along with the failed layer: the membrane (cohesive failure), the membrane bond (adhesive failure), or the substrate (substrate failure).

ASTM D903, Standard Test Method for Peel or Stripping Strength of Adhesive Bonds provides a standard test method for peel or stripping strength of adhesive bonds under laboratory conditions, using highly specialized equipment.⁶

All these test standards are designed to be performed at room temperature, generally around 22 C ± two degrees (72 F ± five degrees), with RH levels at 50 percent (± five percent). Though testing labs can replicate other conditions using additional equipment. This is important because varying temperatures and humidity levels impact adhesion performance.

Temperature and humidity effects

The temperature of ambient air and the substrate can have a dramatic effect on the adhesive performance of air barriers. The adhesive compounds used in air barrier membranes tend to perform worse at low temperatures. Products bonding well at room temperature can lose their strength as temperatures drop; RH can also affect adhesive performance. Some compounds lose their bonding properties when exposed to moist, humid conditions. These factors can impact installation, and limit when and where a particular air barrier product can be used. Whether a project is planned for November in Michigan or for July in Florida, understanding the impact of temperature and humidity on the
air barrier’s adhesive properties is important.

While air barrier manufacturers typically publish temperature ranges in their product specifications, it is important to request independent testing data to ensure these claims are validated by an objective third party. The external third party testing laboratory would have to be accredited by ASTM, ICC, or another organization. This can help ensure the right product for the anticipated site conditions and provide valuable information to defend the specification.

How substrate affects adhesion

The type of substrate and its condition affects how well the air barrier bonds to it. Therefore, adhesion testing must be performed on the planned substrate material. For example, certain cementitious materials may have chemical characteristics, such as high alkaline levels, which are not compatible with certain air barrier materials and some fluid-applied membranes.

The condition of the substrate at the time of air barrier installation is also critical. In many cases, the wall has been poured or erected well before the barrier is installed and may be dirty or dusty from construction activity. Ensuring the substrate is clean and free of contaminants is a basic but useful step to ensure proper adhesion.

Often, a building will comprise a variety of wall materials, such as concrete, oriented strand board (OSB), or other prefabricated materials. In these cases, one should select an air barrier which will bond to all these materials to reduce the number of products specified, and further reduce the risk of installing the wrong barrier on the wrong material.

When using a primerless membrane, ensure primer is not required on all substrate materials. In some instances, differing substrates or different temperature and humidity conditions may require a primer for
a primerless product. Unfortunately, this may not be apparent until the air barrier loses adhesion after installation. Having to then prime the surface and re-install the membrane can cause unplanned delays and additional labor costs. Last minute design changes may result in substitution of a planned material, making it even more critical to have a primerless membrane tested for a wide range of substrates. Rather than relying on manufacturers’ published claims, it is a good idea to request independent testing data to validate the barrier’s primerless bonding performance on various materials. The data can be attained through the third party testing laboratories, as they can test the barrier’s performance without using primer on various substrates and at various temperatures.

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Testing air barrier durability

Since most air barriers will be installed behind exterior cladding and not readily accessible, it is important to select a long-standing membrane. ASTM E2357 defines a standard test method for determining air leakage rate (permeance) of air barrier assemblies.⁷ This involves constructing a specimen wall assembly, including a window opening with flashing and typical wall penetrations such as pipes, vents, and ties, and roof and concrete foundation tie-ins (Figure 1). Varying positive and negative pressures are applied to the specimen wall and air leakage is measured. As noted previously, the air barrier assembly must have an air leakage rate (permeance) no greater than 0.2 L/s/m² (0.04 cfm/sf) at a pressure difference of 0.075 kPa (75 Pa).

ASTM E2357 is designed to provide a realistic evaluation of air barrier assembly performance and helps verify whether the components are compatible with each other. The method has been adopted by the ABAA as part of its acceptance criteria.

However, some manufacturers have gone further, testing wall specimens under real-world, field conditions over long durations of a year or more to assess the effects of time, temperature, and humidity changes on air barrier performance. Leak tests are performed at regular intervals. At the conclusion of the test, the exterior siding is removed to assess any areas of air barrier failure, such as at laps, seams, or penetrations, and any damage caused by common factors. Reviewing a manufacturer’s data from such a long-term field test can provide additional assurance regarding the air barrier’s long-term performance in the real world.

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Additional factors impacting performance

There are other criteria to consider when evaluating air barriers for a project. These include:

Compatibility

To create an effective, continuous membrane, all air barrier components, including flashing and other details, must work together as a system. Using extensively tested products to validate compatibility is crucial. Mixing and matching products which are not designed to work together can lead to failure and allow air leakage at critical points in the structure, especially around windows, doors, and penetrations.

Dimensional stability

Air barriers can vary in quality, which affects their dimensional stability over time. Lower quality membranes can shrink through temperature changes, potentially opening gaps and allowing air leakage. While lower quality products may cost less, any failures leading to a call-back can exceed any savings.

Innovation

Some air barriers are designed with innovative features or capabilities
to save time and/or money during installation. For example, selecting
a fluid-applied barrier designed to be rain-resistant can be useful in climates where rain showers are common, helping avoid weather-related delays.

Track record

Specifying an air barrier with a proven record of performance in different types of applications and diverse climatic conditions can help minimize the risk of failure. Products which have been in the field for years or decades will often have substantial data to attest to their durability and long-term performance. Products without a track record may present a greater risk given their untested history.

 Support

Selecting a manufacturer is just as important as the air barrier itself. The best air barrier manufacturers provide expert knowledge and technical support, help in specifying the right product for the application, and use best practices to ensure proper installation.

Conclusion

Air barriers play an essential role in creating building envelopes which conserve energy, provide healthy indoor environments, and protect structural integrity. When specifying an air barrier, do not overlook the critical factor of adhesion strength. Selecting a membrane with a proven ability to bond will pay dividends for the project, as well as the building owner and its occupants for many years to come.

Notes

1 Read “RR-0412: Insulations, Sheathings and Vapor” Joseph Lstiburek, November 2004. https://www.buildingscience.com/documents/reports/rr-0412-insulations-sheathings-and-vapor-retarders/view[4].

2 Visit “Technical Bulletin on Air Barriers,” Air Barrier Association of America (ABAA).  September 5, 2019. https://www.airbarrier.org/wp-content/uploads/2019/09/ABAA-Technical-Note-2-Air-Barrier-Materials.pdf[5].

3 Refer to ASTM E779, Standard Test Method for Determining Air Leakage Rate by Fan Pressurization. https://www.astm.org/e0779-19.html[6].

4 Refer to ASTM D4541, Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers. https://www.astm.org/d4541-17.html[7].

5 Refer to ABAA T002-2019, Standard Test Method for Pull-Off Strength of Adhered Air and Water Resistive Barriers Using an Adhesion Tester. www.airbarrier.org/wp-content/uploads/2019/05/[8]
S-115-002-rev-0-ABAA-T0002-Standard-Test-Method-for-Pull-Off-Strength-of-Adhered-Air-and-Water-Resistive-Barriers-Using-an-Adhesion-Tester.pdf.

6 Refer to ASTM D903, Standard Test Method
for Peel or Stripping Strength of Adhesive Bonds. https://www.astm.org/d0903-98r17.html[9].

7 Refer to ASTM E2357, Standard Test Method for Determining Air Leakage of Air Barrier Assemblies. https://www.astm.org/e2357-18.html[10].

Author

Iltaz Alam is a product manager at GCP Applied Technologies Inc., and holds a chemical engineering degree. He has more than 15 years of waterproofing experience globally and has encountered several waterproofing and air barrier technologies throughout his professional career

Source URL: https://www.constructionspecifier.com/ensuring-proper-air-barrier-adhesion-for-maximum-performance/

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