Window flashing tape and my own “bathtub test”
I’m trying to settle on which flashing tape to use on the sill of windows. A lot of people seem to use Dow FlexWrap but I am a little concerned about the tape sticking when applied now (as the temps are below freezing). 3M 8067 All Weather Flashing tape is an acrylic which is rated to stick down to 0F so that looks like it has a lot of potential. The main negative with that that I see is since it can’t stretch like FlexWrap, doing the corners is more complicated. 3M has a video showing the installer applying a couple of layers to handle the corners — I’d be interested in hearing if anyone has an opinion on how they are doing that, if they see a flaw in doing it that way, or does that seem acceptable?
I was also curious about how waterproof the tape would be considering there would be seams. I’ve read Martin’s article about a “bathtub” test of peel-and-stick flashings, but this tape wasn’t around then so it wasn’t tested. I decided to do my own simple test for that. I took a small cardboard box and lined it with the 3M 8067 tape. I used the 2″ wide tape so there are actually 3 seams on the bottom of the box that water would sit on top of. I just pushed the tape down with my fingers and filled the bottom of the box with about 1/4″ of water and let it sit. I also put a paper towel under the cardboard box to make it more obvious if it was leaking. I left it for 72 hours (overkill I’m sure but I kind of forgot about it) and was pleased to find no indications of even a drip of a leak. The bottom was totally dry. Now, this isn’t scientific or anything, but considering the water was on 3 seams and I didn’t use a J-roller or let the tape sit for more than a minute before filling it with water, I feel pretty good about the tape’s ability to be waterproof.
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