Think you understand pressure-sensitive adhesives? Think. Again. (EDITOR’S NOTE: Do not try this at home.)
My last post in this series on adhesives, sealants, and tapes ended with this line:
“We hope to follow up this baseline ideal conditions testing with more field-like conditions.”
Introducing the WTF research troupe
Well, it took a while, but we finally got a venue for some more testing of pressure-sensitive adhesive (PSA) tapes: the Northeast Sustainable Energy Association annual conference, BuildingEnergy 13.
NESEA premiered its Trade Show Demo Stages this year, calling the stage demos “Recess for building and energy professionals—Let’s play!” Sure seemed like the appropriate forum for us to premiere the Wingnut Test Facility (WTF), a new round of “benchtop” tape testing with a focus on field conditions: wet, cold, dirty, and just about all of the above.
They actually invited us to come do our tape testing on stage!
Our crack slapstick lab staff
Fellow WTF founder, Dave Gauthier (President of Vantem Panels here in Brattleboro) and I set up the testing this way (download the spreadsheet for details):
- Cold, wet application (no primer)—We put on our jackets and adhered the various tapes to rough OSB outdoors when it was about 28°–36°F (temps rose as we worked; see comments in spreadsheet). “Wet” meant this: we sprayed water from a standard spritzer bottle, then wiped off the OSB with our bare hands—to mimic what might be considered “prepping” the surface on a typical jobsite….
- Cold, wet application (with primer)—We used two priming materials: Pro Clima’s acrylic primer and 3M’s Super 77. We chose the Pro Clima primer because it is appropriate for acrylic tapes, and we had prior experience with it and could easily get ahold of a relatively small quantity from the supplier. We chose the multipurpose 3M Super 77 spray adhesive for the modified bitumen membrane and the butyl rubber flexible flashing product (a specialized primer would have to be specially ordered in quantity).After all the test samples were set up, we stuck them in a freezer, keeping them below freezing until we transported them to the NESEA demo stage in a cooler.
- Dirty application—To reflect another common jobsite condition, we took the substrates outside, smeared mud on them, and then “prepped” the surface by wiping off the excess with the palms of our hands. We did this testing inside at room temperature.
We selected five tapes for this round of testing based on the following criteria:
- They were readily available to us.
- They were all popular with our local building science builder group (http://www.seon.info).
- They provided a selection of different adhesives.
Dave and I and our respective companies—BuildingGreen and Vantem Panels—have absolutely no relationship with any of these companies and no bones to pick or gains to be made with any tape companies, including these.
The five tapes were WR Grace Vycor, Dupont FlexWrap, 3M 8067, Huber ZIPWall, and Pro Clima Tescon No 1.
Rather than hauling Dave’s Constant Rate Extension (CRE) machine down to Boston. we improvised with a spring balance and a hook(see photo). We pulled the sample till it hit a peak or something failed: the adhesive, the backer material, or the substrate (the substrate never really failed, although occasionally chunks of OSB let go before the adhesive or backer did).
No standard test methods currently come close to mimicking the stresses that these tapes will experience in an exterior building assembly—changes in temperature, moisture content, and pressure.
We are using our crude WTF methods to get a preliminary idea of the impact that various field conditions have on the strength and quality of the bond between the tape and the substrate (For a summary of our test results, see Sheet 2 in the attached excel file).
We desperately need better tests that actually reflect field conditions (more on that below).
A couple surprising and telling results from WTF testing. First, Tyvek-FlexWrap: it stretched without letting go up to the 35-pound peak—but ONLY while dry; cold and wet, the tape let go at just 8 pounds. Second, ZIP sheathing tape: cold and wet with water-based Pro Clima primer, it peaked at a disappointing 15 pounds of tension; with the general-purpose 3M Super 77, it peaked at 32 pounds. This might explain why ZIPWall’s recommended primer is solvent- rather than water-based. – Peter Yost
Having said that, Dave and I think the WTF test results suggest the following:
- The substrate makes a really big difference; rough OSB is the most challenging for all of the tapes.
- None of the tapes adhered as well under cold, wet conditions as they did when it was warm and dry. Is this decrease critical in terms of ultimate barrier continuity? We just don’t know.
- When it is wet and cold, using a primer seems to bring tape performance back up.
- For most of the tapes, warm and dirty conditions had far less impact on the quality of the bond than cold and wet conditions did.
4 tips for PSA success
- All PSA tapes and membranes adhere significantly better to plywood than they do to the rough side of OSB.
- When field conditions are less than ideal, strongly consider using a primer, one that is compatible with the PSA.
- Make sure that the primer you select is chemically matched to the tape you are using.
- With all due respect to the WTF, we need serious scientific efforts to determine just how PSA tapes perform under real conditions in assemblies over the long term.
As I was writing this blog post, three important news items popped up:
- Building Science Digest, “Stuck on You”—Joe Lstiburek has quite a bit to say about how different pressure-sensitive adhesive tapes work and his company’s long-term experience and knowledge of tape testing over the last several years.
- Fine Homebuilding, “Backyard Tape Testing”—Martin Holladay has an article on his backyard tape testing in the latest issue of Fine Homebuilding. Martin ends up in the same boat we are: his tests are far from scientific or standardized—and he is the first to admit this right in his article—and his recommendations are couched in the uncertainty of his backyard experiment.
- Pella Window’s internal tape testing—While presenting at a recent conference, a research engineer from Pella let me know that they have done extensive tape testing designed to mimic stresses the tapes see in the field. Pella has tested its own SmartFlash foil-backed butyl tape as well as some other common flashing tapes as part of their installation systems.The researcher sent me some really cool information on their “real-world” tape testing, but only if I kept it confidential, at least for the time being. Watch for more coverage soon!
Next up from WTF’s underground laboratories
We need better tests: one that mimics the “bellowing” effect of wind pressure pushing in and out on the tapes, and one that represents the shear that takes place across the tapes when they are stressed by movement of building components to which the tapes adhere.
WTF is on the job. In my next post, I’ll share some top-secret photos of new testing equipment we’re working on. In the meantime, let us know about any backyard or benchtop testing you’ve done—and what you found out.