Well I just couldn't wait to get a good clamping set up before I made a 1' X 4' panel using the OwensCorning 2' Pink XPS and Gorilla glue. By the way, I have determined that Gorilla Glue and Ashland IsoGrip are basically the same stuff. A one part water activated urethane adhesive. I suspect IsoGrip is a lot cheaper and probably easier to apply (Gorilla ia pretty thick and comes in comsumer size squeeze bottles) Anyway, I built a test panel and just sat some objects on it. Paint cans, a pancake compressor, a bag of salt, ect. It was definately too little despite a fairly good "looking" result.
Along one edge though, there were a few gaps between the foam and panel. I knew my clamping was not sufficient because the panels kept sliding during the early cure. Still this item gave me a good idea of the weight of a completed 2-1/2" panel. It weighed 5 lbs so a 4' X 8' would weigh 40 lbs. That is an R-11 panel with awesone strength. Despite my poor bond the panel can span almost 4 feet and support me with little noticable give. I definately need an even pressure of 4-5 psi to get a reliable bondline.
I also decided to cut my first smaller sample in half and try to butt splice it to see how it would fair. I cut a slot in the foam with my table saw just under the luan facing. I did this on both sides of the panels. Then I cut two luan splice pieces to fit in the slots spanning the butt joint. I put gorilla glue in the slots, wetted the luan pieces, put it all together and clamped. The result is below:
Now a couple things. I just wagged this. The width and depth of the slot were cut by eyeballing so it was a tiny bit wider than the luan splice plate. I think a snug fit would be better. I also did not carefully match the spline width to the depth of the slot. It could be better, but it still the butted piece will support me standing on it like it would before the piece was cut. This seems to be an excellent way to splice 4X8 panels together to make bigger panels and no real thermal break is created. I guess that's why the build SIP homes this way.
Back to work tomorrow flying all week. I'll pick this up next weekend if I have time. I think I have a better idea for a home made panel press than a pool or a vacuum bagging system. I need to figure a bit so I'll put my trip to good use.