This technical bulletin addresses the penetration of fasteners following the installation of AIR-SHIELD air barrier membranes from W. R. MEADOWS. For an air barrier to be effective, it needs to be continuous and so it is imperative that these penetrations be addressed to ensure this is the case.
There are mainly three terms that are discussed in the industry: self-sealing, self-healing, and self-gasketing, all of which get used when discussing fastener penetrations.
The term “self-sealing” is what is used on technical data sheets and seems to be the industry-accepted definition due to the current testing available. To address this, air barrier materials are tested to ASTM D1970 – “Standard Specification for Self-Adhering Polymer Modified Bituminous Sheet Materials Used As Steep Roofing Underlayment for Ice Dam Protection.” The premise of this test is that the membrane is applied to a substrate and two nails are put through the membrane and backed out ¼”. A paint can with its bottom cut out is then installed on the top side of this sample and a second paint can is installed on the bottom side; both are then sealed with silicone. The top paint can is then filled with 5″ of water and left for three days. The result is then recorded as a pass/fail based on the evidence of water in the paint can below the sample. Although not representative of “real-life” conditions, this is the accepted test method currently, although ASTM is examining other methods more representative of the conditions that these membranes will be exposed to.
The term “self-healing” is one that is incorrectly used and not one that W. R. MEADOWS would support. This can be defined as a material that has the ability to heal itself upon damage as a result of removal of incorrect fasteners. This is not a characteristic of the AIR-SHIELD membranes, nor is typical of membranes in the industry.
“Self-gasketing” is a preferred descriptive term and best describes what happens with the correct installation of fasteners as the membrane will create a gasketing effect around the fastener head.
W. R. MEADOWS is frequently asked what types of fasteners are best recommended for use and due to the sheer number of types, this is difficult to answer and should be addressed on a project-by-project basis.
However, there are some basic rules of thumb that can be provided to address fastener installation:
- Screws should be self-tapping (i.e., makes its own hole as it is installed).
- The head of the fastener must be larger than the diameter of the shank.
- The point of the fastener must be no larger than the diameter of the shank.
- The fastener is required to be installed into a solid substrate.
- Fastener installation must be perpendicular to the surface. Any variance in this can create a larger hole than the fastener, creating avenues for air and moisture as the membrane would not have the ability to seal around the fastener.
- The head of the fastener should be compressed against the membrane. This will allow the gasketing effect mentioned earlier
- Overdriven fasteners, or incorrectly installed fasteners, need to be removed and the subsequent hole needs to be filled with BEM from W. R. MEADOWS or another suitable material.
In some situations and with some fasteners, this cannot be accomplished. In these cases, W. R. MEADOWS would recommend all fastener heads be sealed with BEM or another suitable material.
Alternatively, on concrete-related substrates, it is possible that damage to the substrate can occur during fastener installation. In these cases, W. R. MEADOWS’ recommendation is to pretreat the fastener with BEM, followed by the sealing of the fastener head with additional BEM. In the case of predrilling, BEM can be installed into the hole, or the screw threads dipped into the sealant immediately prior to the fastener installation, providing the gasketing effect upon installation.