Octagonal wooden mast section: glue

[Scott Carter]

I've begun scarfing the 20' sections of 3"x8" timbers for the staves of my 85' main mast on a schooner rig. The hollow mast will taper in outside diameter from 16" at the base to 10" tip-top, with the 3" dimension of the timbers being the thickness of the staves. A conventional design using a 22.5 degree bevel running the length of the 8 scarf-lengthened staves will form the octagonal section of the spar, which I'll then hand-form into a circular section.
The wood is similar to Western Red Cedar in terms of grain and density (called Yom Hohm), but a bit heavier. It will be air dried before assembly, but I haven't a moisture meter available to me (southern Thailand) to ensure acceptable (whatever they might be) levels.
I've recently ordered and received 25 big bottles of Gorilla glue (for those of you not familiar, a one part polyurethane, moisture curing, expanding glue). I was in love with this stuff a couple of years ago for furniture, etc., but yesterday's destruction test of a smaller scarf showed glue failure and not wood breaking. I followed and even altered on subsequent tests Gorilla's guidelines e. wetting the surfaces, etc., all with disappointing results. Very little grain breakout on a 13:1 simple scarf of a 1"x1" test piece. All glue failures.
This is disappointing, as other glues have proven unavailable except through personal import ($$$$$$$$$) like West System, Aero-dux, etc.
I need some expert advice here. Can I count on Gorilla for this moderately important element of my boat? Are there any professional wooden spar builders out there? What do you guys use?

[lewisboats]

I think you answered your own question...if the glue fails...you can't count on it...Period.

Steve

[Thin water]

I have had Gorilla glue fail on white pine glued to white pine while making a 14' picklefork hydroplane's frame. I stepped on a floor batten glued to a frame before I screwed it and the glue failed. The wood did not fail. This was not good since this type of pine is not that strong, it is listed as a wood type that Gorilla glue bonds well on their web site and the glue had cured for over one week. It seems to brittle to me when dry causing the breaks when flexed. I have not had it fail when lots of screws were used but I won't use it again unless I have to.

JIM

[Crag Cay]

Yeah, I'm afraid you can't ignore your own testing. If you assembled the joints in as realistically similar way to the method you'll use constructing your mast, then you must believe what you see.

The only problems with trial testing is sometimes you get results from the test peice way better than you can manage on the job itself. This could still be the case with your mast, which is unfortunately even worse news.

[yokebutt]

Scott, two words: Birdsmouth, Epoxy.

[PAR]

Epoxy is an expensive adhesive, but it's strength and gap filling qualities can't be mimicked easily by other adhesives. I don't use the stuff on spars unless it's insisted on, preferring urea-formaldehyde (plastic resin) or Tite-Bond III (modified casein, type I water proof). Tite-Bond has limited gap filling abilities, but requires good clamping pressure and good fits. Plastic resin requires better fits and more pressure and leaves a darker glue line. Resorcinol is a fine adhesive, but it stains the wood, has very limited gap filling (read none), is sensitive to temperatures during the cure and high clamping pressure is needed.

I personally don't like PU adhesives, though some have reliable results, I haven't had the constancy I desire in an adhesive.