Image Credit: All photos: Martin Holladay I filled the test rig with water to see if the peel-and-stick samples sealing the holes would leak. About 45 minutes into the test, I got my first and only leak. Water was leaking through the caps between the end cap and the 4x4 trough. This photo shows Side 1 of the test rig. I used a black marker to re-number the samples. The numbers I wrote in 2001 had faded away. This photo shows Side 2 of the test rig. Sample #14 is MFM Building Products Window Wrap, a product with an "aluminized" facing. After 12 years, almost all traces of the "aluminization" process had disappeared. (Although it looks shiny in the photo, the light is reflecting off a thin layer of transparent plastic, not aluminum.) Other foil-faced products — including Samples #15 and #16 — were still intact; their facings were made from real aluminum. This closeup photo of the 12-year-old sample of MFM Building Products Window Wrap shows that the so-called "aluminized" facing is really cheap plastic. Almost no trace of the "aluminum" color is left.
More than 12 years ago, I wrote an article on peel-and-stick window flashing. The article, “Choosing Flexible Flashings,” appeared in the June 2001 issue of The Journal of Light Construction (JLC).
My article surveyed a variety of peel-and-stick products, including products with butyl adhesive as well as products made from rubberized asphalt. As part of my research, I interviewed industry experts to find out more about the strengths and weaknesses of these materials. I also interviewed builders about their job-site experiences with these products.
Back in 2001, I obtained samples of 21 brands of peel-and-stick flashing and performed a backyard test. First, I built a small wooden “bathtub.” Then I drilled a series of 7/16-inch holes in the bathtub and patched each hole with a sample of peel-and-stick. All of the samples were numbered. Fourteen hours later, I filled the bathtub with water.
I hoped that this backyard test would tell me whether peel-and-stick flashing is really waterproof.
So what were the results? One minute into the test, the first of the 21 brands of peel-and-stick showed signs of leakage. Six minutes into the test, four more products began leaking. After 20 minutes, 12 of the 21 tested products were leaking; then the situation stabilized. The 12 leaky products continued to leak, while the remaining nine products appeared to stay watertight. After 45 minutes, I discontinued the test. (For the record, the nine tapes that didn’t leak were Sealtight Air Shield, Dur-O-Wall Polytite PolyBarrier, Vycor Plus Self-Adhered Flashing, NEI AC Homeseal Self-Adhesive Membrane, MFM Building Products Sub Seal 40, Protecto Wrap BT20XL Building Tape, Ridglass Kwikwrap, Sandell Presto-Seal, and International Diamond Systems Tape Flashing.)
I discussed the results of the test with my JLC editor, who decided that the test wasn’t scientific enough to report. In the published article, I alluded to the test without reporting the individual results: “In an informal JLC test, 21 different peel-and-stick flashings were bonded to wood for 14 hours. About half [actually, 57%] of them failed to make a waterproof seal. Although further curing might have resulted in a waterproof bond, the test shows the need for caution when depending on an adhesive alone to seal out water.”
An accidental archaeological discovery
So why am I recounting this history? Well, the other day I was cleaning out a pile of old lumber under my wood shed, and I came across my homemade bathtub with its double row of peel-and-stick patches. Flash from the past! (Or perhaps I should say, “Flashing from the past!”)
The test rig has not been treated with any special care. At different times over the last 12 years, it has been stored on the dry gravel under my wood shed, or has been leaned casually against an outdoor wall, exposed to the weather. Most of the time, it has been under cover, but without any protection from drifting snow.
Since I recently conducted a backyard test of air sealing tapes, it occurred to me that I could use this 12-year-old artifact to test the tenacity of elderly peel-and-stick tapes. After all, most of us are curious about how these flashing tapes hold up over time. Here was a rare chance to see how samples of these 21 products hold up after years in the field.
Then I had another idea: why not repeat the water-retention test? After all, some peel-and-stick adhesives get more aggressive with age. Maybe some of the products will actually perform better when they are 12 years old than they did when they were newly installed.
A description of the bathtub
Before I describe my recent test, let me describe my homemade “bathtub” in more detail. The test rig consists of a 54-inch-long pressure-treated 4×4 with a V-shaped trough down the middle. I created the trough by making two long 45° cuts in the 4×4 with my table saw. I capped the ends of the trough with spruce end caps, glued and screwed into place. (I used a waterproof glue — either Gorilla glue or resorcinol.)
Once the bathtub was assembled, I drilled a series of 7/16-inch holes along the sides of the 4×4, angled slightly upward. The holes were all aimed at the bottom of the V-shaped trough; when water was poured into the trough, it drained through all 24 holes.
Each hole was patched on the outside of the “bathtub” with a piece of peel-and-stick flashing measuring 2 1/2 inches square. I drilled 24 holes because I hoped to test 24 products. In the end, I had only 21 products to test, so I covered the three extra holes with a product chosen at random (Sealtight Air Shield).
I tested 21 products
Below is a numbered list of the peel-and-stick products I used to seal the 24 holes.
13 holes were covered with rubberized asphalt products:
- 1. W. R. Meadows Sealtight Air Shield, 40 mils. (The same product was also used to cover holes #12, #20, and #23.)
- 2. Carlisle CCW-705 Window and Door flashing, 40 mils.
- 3. Dur-O-Wal Polytite PolyBarrier, 40 mils.
- 4. Grace Construction Products Vycor Plus Self-Adhered Flashing, 25 mils.
- 5. Master Wall Weather Stop Flashing Tape (manufactured by Protecto Wrap), unknown mil thickness.
- 6. NEI AC Homeseal Self-Adhesive Membrane, 30 mils.
- 7. MFM Building Products Sub Seal 40, 40 mils.
- 8. Protecto Wrap BT20XL Building Tape, 20 mils.
- 9. Ridglass Kwikwrap, 40 mils.
- 10. Sandell Presto-Seal, 40 mils.
- 11. Tamko Roofing Moisture Wrap, 40 mils.
- 12. W. R. Meadows Sealtight Air Shield, 40 mils.
- 13. Nervastral Bitu-Rap, unknown mil thickness.
3 holes were covered by rubberized asphalt products with aluminum foil facing:
- 14. MFM Building Products Window Wrap, 25 mils.
- 15. Ridglass Kwiksilver, unknown mil thickness.
- 16. NEI AC FlashSeal, 45 mils.
3 holes were covered by products with butyl adhesive:
- 17. DuPont Tyvek FlexWrap.
- 18. Tyco Adhesives Polyken 627-20 Window Flashing Tape, 20 mils.
- 19. Polyken 626-20 Window Flashing Tape, 20 mils.
3 holes were covered by EPDM flashing products with butyl adhesive:
- 21. Avenco Flashing tape (a flashing tape designed for use on EPDM roofing).
- 22. Geocel 9906 Flashing Tape (a flashing tape designed for use on EPDM roofing).
- 24. International Diamond Systems Tape Flashing (flexible), 70 mils.
How do the samples look?
After 12 years, the flashing samples look like they are in pretty good shape. None of the samples has fallen off, and all of them appear to be well-adhered.
The only odd thing I noticed is that one of the foil-faced products — MFM Building Products Window Wrap — is no longer foil-faced. When I inspected it closely, I realized that the facing was actually made of thin plastic. The manufacturer describes this facing as “aluminized.” I have a different word for it: “worthless.”
In contrast, the aluminum facings on three other products — Ridglass Kwiksilver, NEI AC FlashSeal, and Polyken 626-20 Window Flashing Tape — were still shiny. Close inspection revealed why: these facings were made of real aluminum, not “aluminized” plastic. Caveat emptor.
Repeating the bathtub test
In October 2013, I set my wooden bathtub on an outdoor concrete slab and filled it full of water. All of the 12-year-old peel-and-stick products remained watertight throughout the one-hour test. I was impressed. It seems clear that my original test back in 2001 was performed too soon, when the products had only recently been installed. If I had given the adhesives a few weeks to develop a stronger bond, the products probably would have performed as well as they did when they were 12 years old.
About 45 minutes into my test, a leak developed; one of my glued end caps had failed. The lesson: after 12 years, you can’t depend on a glue joint to remain waterproof. That’s not too surprising. Since the water was leaking out of the bathtub (albeit slowly), I discontinued the test after an hour.
The tenacity test
One day after the bathtub test, I decided to perform a tenacity test. First, I tried to lift each sample by one of its corners, using my fingernails. This proved impossible; they were all too tenacious to be lifted.
Next, I used a putty knife to lift the corner slightly. This, too, was tough. Most of the products stretched before they lifted. Even with a little bit of the corner sticking up, I was mostly unable to peel back the products with my fingers.
There were only two exceptions: Avenco Flashing Tape and Geocel 9906 Flashing Tape. With effort, I was able to peel back these two products. These flashing tapes (also called cover tapes) are designed to be used on EPDM roofing, so they aren’t really designed to be adhered to wood. Moreover, they are quite thick — the thickness of the Geocel product is 70 mils — so it’s possible that the reason that I was able to peel them back was that the thickness of the flashing gave me something sturdy enough to grip well.
In any case, if you are mainly interested in products used to flash windows and doors, the performance of these EPDM flashing tapes is irrelevant.
The results surprised me
The was a limited and unscientific test. The test conditions were not carefully controlled. The test involved only a single substrate (Southern yellow pine lumber), so the results tell us nothing about how well these flashing tapes might stick to housewrap, or vinyl window flanges, or rigid foam. Nevertheless, the results were interesting and even surprising.
Because of my background as a roofer, I’ve always had a keen interest in flashing. I tend to favor flashing solutions that depend on overlapping layers rather than sticky tapes, because “physics trumps chemistry” in the long run.
Before I conducted these recent tests, I would have guessed that some of the 21 products I installed 12 years ago would have failed by now. I would have been wrong.
I salute the manufacturers of these peel-and-stick flashings. They are selling products that appear to improve with age.
Martin Holladay’s previous blog: “Fixing a Wet Basement.”