More on the Loctite Polyurethane Construction Adhesive story: Placed too much faith on a line in this article about polyurethane adhesives expanding and filling gaps as they cure: https://www.popularwoodworking.com/article/the_truth_about_polyurethane_glue
"While it’s true that polyurethane glues expand as they cure (the squeeze-out actually foams up like aerosol insulation), glue experts agree that polyurethanes cannot fill a gap larger than 1 or 2 millimeters. After a millimeter or two the foam has no strength, so it is merely a cosmetic filler." And I believed another article that said all polyurethane glues are basically the same. They aren't. <https://lh3.googleusercontent.com/-eRa4FP2ZLjU/WbWEMLfm3tI/AAAAAAAABUM/IwTlM2Ww_cA2r6IZ5U2OFo-8oP8aDRxwACLcBGAs/s1600/IMG_20170910_121558.jpg> I used Loctitite's Polyurethane PL Premium Construction Adhesive. The Loctite, while seemingly inexpensive for a polyurethane glue at $7 for 28 oz., is not comparable to Gorilla Glue -- which in an earlier test worked superbly in bonding polyiso to polyiso, but is extremely expensive for the purpose. Loctite, as you can see in the photo, is not a thin, amber, translucent liquid: It has a MUCH higher vicosity. When squeezed from the tube onto vertical polyiso facings, it did not stick but fell to the ground. I squeezed it into a paint tray and used a putty knife to apply it in a thin coat onto one of the two four inch by eight foot edges I was bonding. It took seven ounces to coat the face of one edge. I misted it with water before fitting the pieces together and clamping. The official instructions say: "Apply adhesive to one surface of the material being bonded. Press the surfaces firmly together. Materials may be repositioned within 45 minutes after applying the adhesive. If bonding two non-porous surfaces (such as foam, metal and fiberglass), add water in the form of a very light or atomized spray from a plant mister bottle to the extruded adhesive. The repositioning time will then be reduced to less than 30 minutes. Use mechanical support for 24 hours while the adhesive cures." Was expecting to see expanding/foaming action as with Gorilla Glue, but there was none. And in fact, Loctite doesn't promise any, only that it will not shrink.That was my first disappointment. My misunderstanding. While cleaning my putty knife, I smeared a bit on another piece of polyiso on which I was going to test its compatibility with my paints and primers and sealants. It was dried and hardened to touch within 15 minutes -- without being water-misted. That was a second disappointment. Loctite said you have 45 minutes of repositioning ability without misting and 30 minutes with. Also will note that it had no tacky, grabbing properties at all, when spread in a thin coat. But my biggest disappointment was the next day when after cure time had passed, I unclamped the "bonded" pieces. As I lifted slightly on one side to reach and release a second clamp, I heard a cracking noise and the boards split apart at the bond. This very likely could be due to my having "troweled" it on in a thin coat with a putty knife. Perhaps it would have bonded more strongly if I had been able to position the board so the face to which the glue was to be applied was horizontal instead of vertical and had squeezed onto it a 3/8" inch bead of material and then misted that and let it squish and spread a bit as I squeezed the two pieces together to clamp. But that would possibly have used the full 28 oz tube just to zig-zag one beadline along the 4-inch wide, eight-foot length. And would not have given me the full face-to-face bonding I got with the Gorilla Glue experiment and earlier successful Liquid Nails experiment. And would have made using Loctite for this project potentially even more expensive than using Gorilla Glue for it. My impression is that Loctite polyurethane Premium Construction Adhesive is not a good choice for permanently attaching polyiso boards to one another. To keep my project moving forward at this point before winter sets in, I can't devote time to more tests of more materials. So I am going to go with the Liquid Nails. -- You received this message because you are subscribed to the Google Groups "hexayurt" group. To unsubscribe from this group and stop receiving emails from it, send an email to hexayurt+unsubscr...@googlegroups.com. To post to this group, send email to hexayurt@googlegroups.com. Visit this group at https://groups.google.com/group/hexayurt. For more options, visit https://groups.google.com/d/optout.
