Tapes, tapes, tapes
I’m about to start putting up continuous exterior insulation on my walls, with seams taped as the primary water barrier (primary air barrier is a membrane behind the foam, though.) Due to supply chain issues, the polyiso foam I ended up with is Johns Manville AP Foil Faced, which is specified for this purpose per their instructions (https://www.jm.com/content/dam/jm/global/en/building-insulation/Files/BI%20Toolbox/BID-0150-Residential-AP-Foil-Above-Grade-Exterior-Walls-9.10.13.pdf)
Referencing the first page of that document, they suggest “Flashing tape such as 3M 8067, Grace Vycor Pro, or Lamatek”
Referencing BSI-067 (https://www.buildingscience.com/documents/insights/bsi-067-stuck-on-you), Joe Lstiburek says: “Most butyl tapes are typically called “flashing” tapes and the acrylic tapes are typically called “sheathing” tapes. The butyl tapes are “thicker” and are “gooey” on the back. The acrylic tapes are very thin. The butyl tapes handle movement better than the acrylic tapes. The acrylic tapes “stick” better – they stick unbelievably well. The acrylic tapes are often used to “terminate” the top edge of a butyl tape. This is necessary as butyl tapes can fishmouth – their top edge peels away or roll away over time – as such their top edge needs to be “terminated”. This type of fishmouthing with acrylic tapes does not occur. Although most flashing tapes are butyl, advances in acrylic technology have allowed a limited number of acrylic tapes to function as both flashing tapes and sheathing tapes.”
3M 8067 is acrylic-based and sold as a flashing tape — apparently one of the “limited number” that Lstiburek refers to?
Grace Vycor Pro is butyl-based and sold as a flashing tape — per Lstiburek, using this tape woudl require terminating the top edge with an acrylic-based “sheathing tape”, though the Johns Manville instructions don’t mention this.
Lamatek appears to be a manufacturer of a variety of tape-related products, not a specific type of tape.
My air barrier membrane is Adhero, and my interior vapor retarder is Intello, so I’ve also been using a lot of proclima tapes — Tescon Vana and Contega Solido Exo — which are acrylic-based and simply sold as “tape”. They’re also pretty expensive.
So, I’ve got foil-faced polyiso (which, according to some of martin’s old articles, is generally one of the easiest substrates to stick to.) The foam manufacturer is recommending an acrylic-based flashing tape, a butyl-based flashing tape, or a manufacturer of tapes. It feels like the Proclima acrylic-based tapes would probably work fine. It also feels like I should use something directly mentioned in the foam instructions so the building inspector doesn’t have any question about it. Of those choices, the 3M 8067 is acrylic-based and thus (per Lstiburek) shouldn’t need any special treatment at top edges — and is also a fair bit cheaper than Tescon Vana. Is this a reasonable conclusion to go with?
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A lot has changed since that BS article was written. Acrylic tapes are way more readily available these days and many of them (Zip, 8067, Siga, Pro Clima) work really well.
> It feels like the Proclima acrylic-based tapes would probably work fine.
Probably. Like you said, though, expensive.
> It also feels like I should use something directly mentioned in the foam instructions so the building inspector doesn’t have any question about it.
If your inspectors are checking this level of detail, I'd be impressed yet annoyed!
> Of those choices, the 3M 8067 is acrylic-based and thus (per Lstiburek) shouldn’t need any special treatment at top edges — and is also a fair bit cheaper than Tescon Vana.
8067 is a great tape and readily available on Amazon. I would not hesitate to use it. My house has many football field lengths of it all over the place.
+1 on on the 8067 tape. I have also used it to tape 1.5" JM polyiso with the foil face, and at this point, I'm certain that removing the tape means removing the polyiso facer with it.
FWIW I also used a foil faced tape, Nashua 324A, available from HD and pretty much everywhere, and it worked great. It is also an acrylic based tape, with a backer, and once in place and rolled it doesn't appear to be removable. The service temperature is stated well within my normal range, -20°F to 325°F. I wouldn't hesitate to use it either. It's also cheaper than 8067.
Follow-up on this for posterity:
I went ahead and ordered a bunch of 3M 8067, and it's working great. I'm using 3" to tape the seams, 4" cut into squares to tape over screws, 4" on inside corners (since the backer is split in the middle, vs. the 3" which has one narrow and one wide strip), and 6" on outside corners. Some quick notes / a tape review of sorts:
-This stuff is sticky! There's no room for error -- especially with the (quite weak) JM AP Foil Faced facers (which tear if you look at them wrong) -- if the tape touches the insulation anywhere, it's basically stuck; I'm confident that it's not coming off.
- It's also a bit smelly -- I wouldn't recommend using it indoors, but outdoors it's whatever. When the UPS woman delivered a case of it, she commented "I've got a package for you. It's tape. I can smell it and it's been stinking up my truck!" Proclima tapes have a slight odor too but not as strong as the 8067.
- It's somewhat stretchy -- though it's best if you pre-stretch it before applying it if you need it to be stretched, otherwise it has a tendency to spring back.
- The biggest complaint I have with it is that the backer tears easily (much more easily than the Proclima backers), so it's a pretty frequent occurrence that you're working on a long stretch and the backer will tear midway and you need to get your fingers back behind the tape to re-start it.
- My other complaint has nothing to do with the tape, and everything to do with the insulation. The JM AP Foil-Faced comes with little lines molded into it to make it easy to cut into 16" or 24" widths -- but since I'm applying full panels on the exterior, these just get in the way and make a lot of little channels behind the tape. The 3M tape's flexibility helps with this, as you can kind of press it back into the channels, it's just annoying and doesn't inspire confidence.
- For the record, Proclima tapes also stick just fine to the polyiso, and I'd say I think I like them a little better in general, but 8067 is half the price and is doing a fantastic job.
Summary: I would buy / use the 3M 8067 tape again, for exterior applications. I would not, however, use JM AP Foil-Faced again -- the facer is just too easily damaged to inspire confidence in its long-term ability as a WRB. (Also, no matter how carefully you cut and vacuum, little foam bits end up everywhere -- I suppose that's another advantage of mineral wool or wood fiber insulation, the bits that end up in your yard are "rocks" or "wood" not "plastic & foil" -- but that's another story!)
I've used miles of 8067 on my foam sheathing - inside and out - and can attest to its durability. It's held up perfectly even when exposed for several years.
Yes, some of those tapes are pretty smelly, especially when you're actively using them. I don't really know why, but the smell doesn't seem to persist long after you apply the tapes.
I like using the Nashua 324A tape with polyiso because it matches the foil facer and gives a nice, clean look of a solid wall of foil facing when used (probably the OCD part of the engineer in me :-). You don't really NEED a foil tape here, but it does look nice on foil faced polyiso.
BTW, did you have to clean the Johns Manville polyiso to get the tape to stick? I just recently (a few days ago) did a small project with some of this polyiso, albeit polyiso bought several months ago, and I found it had very thin layer of oil-like material on it which I assume was a release agent from the manufacturing process. The tape didn't want to stay stuck until I wiped the areas I was taping with isopropyl alchohol prior to taping. Once I cleaned the surface, the tape stuck like crazy like I was expecting.
Bill
Huh, I haven't seen any issues with anything oily on the surface -- for me, if the tape lightly touches the facer, the facer's coming off with it most of the time! The only thing I've had to clean off is all the dust and crumbs from cutting it, which like to cling to the surface and prevent the tape from sticking -- I just brush it clean with my hand before taping.
Now that you mention it, taping with foil tape would be satisfying! But, I already have a case of 8067 and it'd be very un-satisfying to switch appearance in the middle of the job ;)
I had a lot of "Warehouse dust" on mine that I had to remove first, that black soot-like thin layer of dust that comes with everything. A quick wipe around the edges with a wet paper towel was all that it seemed to need.
Mine as actually a very thin oily film. I noticed the sheets were really slick, and my fingers were slick after handling them. There was nothing visible, and it wasn't gooey or anything like that, it was just the very slightest film of something oil-like. Isopropyl alchohol took it right off, so it wasn't a big deal once I realized the tape wasn't really sticking the way it should. Acrylic tapes should normally stick like crazy to that foil facer.
Bill