I stated in my original post that this application will probably squeeze most of the glue out from between the plys.
++++++++++++++++++++++ Scott I honestly believe that this glue has a place in building airplanes, so I will risk getting flamed here. A similar discussion on another interest group site some months ago provoked me to do a fair amount of research and tests with Urethane glue - the up-side to this adhesive was very compelling. If I can find the links, I will pass on some of the stuff, in particular a well written report from Forest Products, they tested several brands. The short story is that Urethane adhesives are more than adequate and have some nice plusses provided you understand HOW and WHEN to use them. My initial tests had me believing pretty much what Mark L believes, but the potential benefits gave me the incentive to look deeper. I am glad I did. All my ply scarf joints are now done with this adhesive - the break test results are more consistent than any other adhesive - zero failure - in fact, I have not been able to separate a joint yet (birch ply). On the other hand, I will not use Urethane unless I am sure that I can get to and clamp every square inch to a flush fit - NO GAPS. I mostly use it where the glue area is large (relative). Typically, not on a block gusset, but Ok for a ply plate gusset. When I get to doing what you are doing, laminating the wing tip, HS and VS bows, I will not consider anything else. This adhesive will tolerate an extended open time - may be a plus for laminating long bits. I have not tested this, but FP says that opening and closing the joint several times before final clamping had no ill effects on the joint We sometimes tend to consider the strength of the glue (psi) in isolation, but how well the adhesive bonds to any given material is also a factor. I have seen epoxy joints fail many times during my RC flying years, with the bulk of the epoxy remaining (in tact) on one side of the failed joint and what resembles a finger print of the joint on the other side. The fact that I could probably drill and tap a hole in the epoxy did not help matters, the joint (not the glue) had failed. Agreed, this was 5 minute epoxy, not T-88 but I mention this to make the point - even an incredibly strong glue must actually sticks to the host material - urethane does this better than anything else (except cyno). I will not use Urethane in a cluster joint - I believe that actual strength of the glue now becomes more significant due to a reduced adhesive contact area - and the intrinsic strength of epoxy (psi) comes into play. For what it is worth, in some of my tests, even a 10mm staple (thru 4mm ply) on a 30mm (1.3"?) spacing was not enough to keep the surfaces tight when the glue started fizzing. I guess this pressure may force glue into the fibres if the joint is well clamped. Steve J Port Elizabeth South Africa
