by Katie Daniel | December 14, 2017 2:25 pm
by Anthony M. Garcia, PE, and Jorge M. Blanco
Construction tapes and flashings are used to span joints and gaps, typically in conjunction with a primary water-resistive barrier (WRB) or air barrier. Since they are concealed behind cladding, it is important tapes and flashings are durable. Will they remain adhered in harsh conditions? Can they accommodate movement for the design life of the building? This article’s authors performed hundreds of tests to evaluate different tape adhesive chemistries and durability on a variety of substrates.
Most construction professionals are familiar with traditional rubberized asphalt self-adhered flashing (i.e. peel and stick), but acrylic and butyl tapes are increasingly popular. Construction tapes and self-adhered membrane flashings (collectively referred to as ‘tapes’ in this article) are used to span gaps and transitions in materials, such as at window perimeters, sheathing joints, and other complex geometries.
Tapes are common accessories in WRBs and air barriers such as sheet membranes, liquid membranes, and building wraps. These assemblies are crucial to a building’s performance and durability. Since tapes are used at junctions critical for keeping the exterior out, proper selection and installation are paramount to avoid water infiltration and air leakage that may lead to tenant discomfort—or worse.
Defining the tapes
To define ‘tape’ and its function in construction, the authors reviewed numerous codes and standards, including the 2015 International Building Code (IBC) and 2015 International Energy Conservation Code (IECC).
Regarding WRBs, IBC requires:
[n]ot fewer than one layer of No. 15 asphalt felt, complying with ASTM D226 [Standard Specification for Asphalt-Saturated Organic Felt Used in Roofing and Waterproofing] for Type 1 felt or other approved materials, shall be attached to the studs or sheathing, with flashing as described in Section 1405.4, in such a manner as to provide a continuous water-resistive barrier behind the exterior wall veneer.(This comes from the 2015 IBC Chapter 14, Section 1404, Paragraph 1404.2.)
Flashings, as defined by IBC:
prevent moisture from entering the wall or to redirect that moisture to the exterior”, and “shall be installed at the perimeters of exterior door and window assemblies, penetrations and terminations of exterior wall assemblies… (See 2015 IBC Chapter 14, Section 1404, Paragraph 1454.4.)
IBC does not require or define an air barrier. However, IECC calls for an air barrier to be “continuous” and “provided throughout the building thermal envelope.” (Excerpted from 2015 IECC Chapter 4, Section C402, Paragraph C402.5.1.) For the air barrier, IECC also requires:
joints and seams shall be sealed, including sealing transitions in places and change in materials…Joints and seals associated with penetrations shall be sealed in the same manner or taped or covered with moisture vapor-permeable wrapping material.(See 2015 IECC Chapter 4, Section C402, Paragraph C402.5.1.1.3.)
(The code specifically mentions “tapes” as part of the air barrier.)
As IECC recognizes tapes will be stressed during their service life, it requires sealing materials to be “securely installed around the penetration so as not to dislodge, loosen, or otherwise impair the penetrations’ ability to resist positive and negative pressure from wind, stack effect, and mechanical ventilation.”
In addition to codes and standards, previous research and laboratory testing on WRBs informed the study discussed in this article. (For more information, see the February 2015 issue of The Construction Specifier for the article, “Durability of Water-resistive Barriers,” by Beth Anne Feero, EIT, and David H. Nicastro, PE. Visit www.constructionspecifier.com/durability-of-water-resistive-barriers.) During the construction of the WRB specimens for testing, manufacturers’ accessory tapes were installed at many details; this experience helped develop tape testing methodology and provided a basis for product selection. Ongoing WRB testing will continue to inform future tape testing.
For this study, tapes were defined as broadly as possible, while keeping IBC, IECC, and colloquial definitions in mind. The requirements for inclusion in the testing were purposely flexible.
Tapes typically consist of similar components, including a carrier sheet (i.e. facer or scrim)—often made of polyethylene, polypropylene, or aluminum—and an adhesive layer. A release paper (protective liner) is used on some products; one of the most challenging aspects of engineering a sticky tape is keeping it from adhering to itself on the roll.
The adhesives used in tapes consist of long-chain polymers that interact with substrates under pressure. The polymers create physical bonds that must be very strong in the dynamic and critical applications of building tapes.(The Scientific American article, “What Exactly is the Physical or Chemical Process that Makes Adhesive Tape Sticky?,” can be read online at www.scientificamerican.com/article/what-exactly-is-the-physi.)
Generally, the market is dominated by a few adhesives and their specific uses:
Why test tapes?
Experience in forensic investigations indicates tapes are prone to failure, which can be discovered due to water infiltration or the consequential structural damage. Tapes require careful installation, but manufacturers’ requirements vary, including rolling with a hand tool, limited effective temperature ranges, use of primers, treating the tape edges with sealant, or other specific procedures. Despite these requirements, tapes are often installed by untrained laborers that have never read the installation instructions or product information.
Tapes must adhere to a variety of substrates, which may be dusty or wet due to construction activities. The tapes must remain uncovered until the building is clad, exposing their free edges to abrasion, ultraviolet (UV) light, and weathering—harsh conditions that may cause curling, wrinkles, ‘fishmouths’ (Figure 1), or other failures.
Additionally, it is common to see one manufacturer’s tape used to flash an opening by adhering to another manufacturer’s WRB. Although not an approved assembly, tapes must often stick to products other than the manufacturer’s own. Incompatibility between tapes and substrates may cause leaks at the openings, penetrations, or, worse, at concealed locations within walls. Repairs are not trivial, since the products are concealed by cladding, requiring costly demolition and reinstallation. The WRB, including tape accessory products, must last for the design life of the building.
Due to the importance of tapes in building envelopes, specifiers must have confidence in their performance under a variety of circumstances. Manufacturers’ product information is often incomplete, offering only general information—actual conditions may not meet the requirements provided by manufacturers.
How to test tapes
A variety of test methods and requirements published by ASTM and the Air Barrier Association of America (ABAA) were considered for this research. It would be ideal to test tapes’ ability to perform a variety of functions, including:
It is extremely difficult to include all possible variables in a single test, so an initial procedure was developed to look at the performance of construction tapes in a multi-faceted way.
The pull-off adhesion test, often called the ‘puck test,’ is often used in-situ to test membranes, including tapes. A pull-off adhesion of 110.3 kPa (16 psi) is required by AABA, but pull-off adhesion (i.e. tension) may not reflect actual behavior in construction, where tapes usually have to resist movement in plane. (For more information, see Revision 14 [June 2015] of the Air Barrier Association of America’s “ABAA Process for Approval of Air Barrier Materials, Accessories and Assemblies.”)
By analogy, consider separating an Oreo—it is most difficult to pull the cookies off the frosting in straight tension (and the cookies usually break). Instead, it is easier to pull cookies apart by twisting (i.e. torsion, which does not relate to typical construction) or by sliding (i.e. shear, as in ASTM D3654, Standard Test for Shear Adhesion of Pressure Sensitive Tapes). (The authors are grateful for the suggestion of this analogy by Dr. Christopher C. White, a research chemist with the National Institute of Standards and Technology [NIST].) These different directions of force application yield drastically different strength values. However, they are measuring the same adhesive property, so higher values from direct tension may give a false sense of security—and misleading information about durability. The authors believe shear adhesion is the appropriate way to measure the adhesive strength of construction tapes.
The selected initial test method is based on the ASTM D3654 procedure for measuring adhesion in shear, and was modified based on experience to include:
Numerous tapes made with different types of adhesive were tested on a variety of substrates. The rack can hold 48 specimens to be tested at a time, allowing for data collection on a large number of combinations. Other variables tested included using or omitting recommended primers, using mechanical rollers
or hand pressure, and varying the ‘rest’ time before exposure. Since pressure-sensitive adhesives often take time to develop full strength, researchers wanted to determine if these variables affected tape performance.
The test procedure is summarized as follows:
What were the results?
So far, testing on this rack has included 360 specimens with seven acrylic, five butyl, and six rubberized asphalt tape products from eight manufacturers, in various combinations on the following substrates:
In addition to sheathing substrates, tape-to-tape adhesion was tested to evaluate lap performance, since all tapes will be adhered to themselves at certain details. The authors were surprised when failure occurred at the interface between the tapes (Figure 6) more than twice as often when compared to other substrates at the same location.
The carrier sheet played a prominent role in the durability of the tapes under loaded and exposed conditions. The authors observed two failure modes:
The data collected is extensive; averaged results are shown in Figure 7). The following conclusions are of particular interest.
The 30-day limit was imposed after analysis of preliminary results and with a desire to collect data rapidly. Most specimens failed within the 30-day limit, but some well-performing specimens during the preliminary tests were removed from the rack (without failure) at approximately one year of exposure. If a specimen exceeded the 30-day limit, it would generally reach the 180-day exposure limit imposed by most manufacturers’ literature.
What are the next steps?
This testing is ongoing. Based on experience with construction failures and knowledge gained from the study so far, additional combinations are planned, including the following additional substrates:
It is important to note numerous conditions can affect tape performance beyond the initial study’s scope (although the conditions may be simulated during future testing). They include:
In addition to the shear adhesion testing, long strips of tapes were installed on sheathing to observe how tapes behave with environmental exposure, as shown in Figure 11. Qualitative evaluations include shrinkage, bleeding, curling, and spontaneous development of ‘fishmouths.’ Future testing will include pull-off adhesion per ASTM D4541, Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers, and peel adhesion to compare the results to these shear adhesion tests.
Every layer matters in a building’s water-resistive barrier or air barrier, so the importance of tapes cannot be overstated. Common in construction, tape failures lead to costly repairs. The testing confirmed typical field observations—when installed well, most tapes perform acceptably, a few are exceptional, but some perform very poorly.
The industry needs standard test methods reflective of tape conditions in the field. Most current methods load tapes in unrepresentative manner or are impractical to perform. The test developed for this study simulates the forces tapes experience in construction better than other methods.
A few techniques and best practices to improve the durability of tapes were illuminated by this study. Even if the best tapes are specified, installation is critical. One should use compatible primers when provided by the manufacturer, especially on OSB sheathing. Pressure should be applied with a roller in all situations. Tapes should only be used with the recommended substrates and WRBs.
Additionally, specifiers must be aware of performance limitations of tapes in WRB and air barrier applications, including their ability to adhere to substrates and adhesion to a tape’s own carrier material. Where possible, one should specify the ‘smooth’ side of OSB as outward-facing to optimize adhesion by tapes.
Anthony M. Garcia, PE, is a project engineer with Building Diagnostics Inc., specializing in the investigation of problems with existing buildings, designing remedies for those problems, and monitoring the construction of the remedies. He participates in the research being performed at The Durability Lab, a testing center established by Building Diagnostics at The University of Texas at Austin. He can be reached by e-mail at email@example.com.
Jorge M. Blanco is a graduate student studying Civil Engineering at The University of Texas at Austin. He serves as a graduate research assistant for The Durability Lab, which researches and tests the durability of building components, identifying factors causing premature failure. He can be reached via e-mail at firstname.lastname@example.org.
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