Defining and testing construction tape and flashing durability

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:

• CDX plywood sheathing (plywood);
• ‘smooth’ side of oriented strand board (OSB) sheathing;
• ‘rough’ side of OSB sheathing;
• OSB with integral WRB;
• glass mat-faced gypsum sheathing; and
• extruded polystyrene (XPS) insulation boards.

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:

• carrier sheet separated from the adhesive and slid vertically (Figure 5); and
• adhesive disbonded from the substrate (Figure 5).

The data collected is extensive; averaged results are shown in Figure 7). The following conclusions are of particular interest.

1. Only 95 specimens (26 percent) reached the cutoff time of 30 days without failure. Almost half the specimens reaching this point were acrylic tapes. Still, the average time of failure for all acrylic tape tests was much lower, as shown in Figure 8.
2. Across all combinations, butyl tapes had an average time to failure of 10 days; rubberized asphalt tapes had an average time to failure of six days. (See Figure 9.)
3. Modified asphalt tapes performed best on XPS insulation, with an average time to failure of 11 days.
4. Butyl tapes performed the best on gypsum sheathing, with an average time to failure of 13 days.
5. The ‘rough’ side of OSB was the most challenging substrate for all adhesive types, with an average time to failure of seven days. In contrast, the average time to failure on the ‘smooth’ side of OSB was nine days. (See Figure 10.)

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:

• polyisocyanurate (polyiso) insulation;
• vinyl (to simulate the window flanges on typical multifamily construction);
• aluminum (to simulate common window frame and flashing materials);
• various type of steel with and without corrosion (to simulate lintels, flashings, and other common construction details); and
• common WRBs (including building wraps).

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:

• adverse storage conditions—most tapes call for storage in a cool, dry location, which may not occur on construction sites;
• wet substrates of all varieties to simulate installation of tape during or shortly after rain; and
• dirty substrates to simulate installation of tapes on active construction sites.

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.