Seconded Woodie's idea that you can use HHG to close a box. Remember many companies used HHG for everything back in the day they didn't have modern glues.
The most interesting method that I have ever seen to use HHG to close a box was from Mario and he made a video of him doing it and maybe someone can find it it was once posted on the OLF.
Mario exploited the idea of glue viscosity and thicker viscosity in his method which was the fascinating part to me. He pre heated like Woodie suggests and then used thicker viscosity of HHG and laid down a heavy, thick bead on the top side of the rim. He did not apply to the top at all but IIRC he did preheat the top with a heat gun as well as the rim.
Mario relied on the thicker viscosity of his HHG to form a thick, tall bead around the rim that the outer layer would cool first thusly encasing the inner layer of liquid glue and helping to keep it warm a bit longer.
Think Tylenol gelcaps....
Then he places the back, preheated again, on the proud bead/gelcap all around the rim and as he applies the clamps the bead is broken, the liquid, HHG runs out and distributes on all the horizontal surfaces of the linings and sides with excess squeeze out visible and ready to be wiped up. I think he also reheated the rim with the heat gun just where the back met the rim to be sure the liquid HHG did flow everywhere and then he called it a day.
Beautiful! I may have some of his method wrong of course it was over ten years ago and I only saw this video once.
I'd ask him, we are friends on Facebook if he still has the video but he was one of the pros who left the OLF because of the know it alls who don't and I understand how he feels about this and respect him greatly.
But what a great method.
One last thing I think the world of my friend John Hall and I was not going to bring it up but there are many posts here on the OLF of fish glue failures and when this is brought up it often devolves when someone tries to protect what they believe for better or worse.
We used it, bought directly from Norland who was the only maker stateside back 18 years ago when we bought ours and they may be still I'm not up on it. We are in Michigan and have a thing called or used to have a thing called winter. I can't remember the exact numbers but within 6 months, seasonal change we had a bridge lift. We had used Fish glue, handled it exactly as Norland prescribes and even parted it out into sterilized Mason jars so the bulk would stay fresh and we stored it in our fridge.
Then another lifted bridge came back and of course we repaired this at no charge and with HHG. We went though our receipts and proactively contacted a two dozen of so bridge reglue clients and offered them free reglues with HHG. Of the maybe 9 that came back there were lifted back edges on three of them IIRC that had not been noticed yet by the owners.
We pitched or Fish glue and never used it again for anything.
So we are not alone I would estimate 2 dozen posts on the OLF of people who had Fish not hold up when the humidity rises even though it never harmed the fish swimming in the ocean and they did not fall apart...
If your instrument may sometime in it's life live where the humidity may be higher I would not recommend Fish glue use at all and especially for bridges. It really set us back and cost us in both opportunity costs and our reputation and we can't have that.
Now that someone came out as not being a fish fan others may relate what fell apart for them.
But back to HHG it's a great solution and it can be fun too to learn how to work with it. We've always fancied a hot room like the violin makers use where it's 125F maybe and you do your gluing in your boxers unless of course you go commando.
Lastly if you build a classical with less tension than a steel string, keep the instrument in a humidity controlled case and never really subject it to the rigors of a traveling, gigging musical Fish may work for you but I still would not recommend it.
I'm sad to have to share this Fish was in all other ways very attractive including how hard it dries and it still is reversible.
I have a bit of a dispute unfortunately happening over one of my tutorials more specifically the nut slots. What is behind the dispute is a very basic idea that I doubt the other parties would even agree is in play here. You do not set-up a guitar for the best case situation with the light hitters you set up a guitar in some cases for Pete Townshend and if you don't know how someone hits you favor the higher side so they don't have to come back unless it's with a second guitar for more set-up.
Likewise do you build for the idea that it will be kept in a humidity controlled case, adult owned, cared for very well and never leave the house? Or do you build for one of my clients who did leave a Heshtone in a hot car in Nashville for a week while he was doing session work and got drunk and put in jail? My bridge did lift by the way and it was glued with HHG.
