I see something here
A LIGHTLY CHAMFER THE EDGES SO YOU ARE SURE YOU ARE WOOD TO WOOD
b SAND THE AREA BEFORE GLUING 80 GRIT
c APPLY GLUE TO BOTH SURFACES
d WORK FAST
e CLAMP FOR 24 HRS

The finish is working like a shim and you are relying on the glue only you want to be sure you have wood to wood contact . DO NOT OVERTIGHTEN the clamp

I have been using LMI white for bridges on T-Top guitars. I use fish glue for the bracing as I have heard from respected luthiers. I have my own working hypothesis on why that works well and of course I am going to state it

Fish glue has a long open work time, pot life. T-Wood is very hydrophobic. So the long open and long cure time of Fish glue, and to some extent AR glues especially TB extend, so it has plenty of time to wet both surfaces and stay wet long enough to get into the T-wood fibers and then chemically bond. HHG gels really fast.

That's my working hypothesis and I'm stickin' to it

All the bracing and bridges get clamped for 24 hours.

See my comments in the 'Torrifying Tone Wood' thread linked below re: issues with bridge retention on highly torrified tops.

http://luthiersforum.com/forum/viewtopi ... od#p708865

In summary, we were able to keep bridges on the Martin D-35 Anniversary Models with VTS European spruce tops without issue during a time when the factory and many of their repair people were not able to do so. After what was reported to us as 'numerous bridge joint failures' of both production and repaired guitars, Martin opted to re-top warranty bridge repairs on those guitars with a Level 1 top (lowest level of torrification from supplier) and stopped using highly torrified tops on any of their instruments.

At Martin's request, we documented our process and passed it to them, but I never did see any feedback as to whether the repair people or production line altered anything with regards to their VTS system process for bridge glue-up beyond what was already mentioned above.

The method used at Greenridge was a variant of our standard bridge reglue: meticulous surface prep, a light scrape of the spruce patch at the last possible moment before glue-up, fresh standard mix 315g HHG, heating the bridge to 150 deg F (entire bridge - not just a blast of heat on the glue surface), glue applied to both surfaces, then a third, heavy coat on the patch just as the bridge went on. By the time the clamps were on, the bridge dumped heat into the glue patch and the usual five-clamps went on for a 6-8 hour clamp. As mentioned before, the major difference with 192g and 315g bridge glue-up is the ability to load the joint in as little as 3-4 hours with the higher gram strength glue.

I am headed back to Greenridge over my next three-day weekend to continue helping with the post-COVID dig-out... four neck resets and an early 2000's stump-wood Beardsall with 90 running inches of cracks on the back - all showed up in the past week and more on the way, plus what was already in work before Hurricane 'Rona swept through the shop. Also a couple of bridge reglues and one restoration/conversion of a pretty little 1927 O-18K that I most likely will take measurements on once the neck and bridge are off.

I'll get an update on the information above reference torrified top/bridge joints and post if anything has changed.

Hey JF, meant to ask earlier - have you done very many with the LMI white? And what's your process??

I've used fish glue in the past and had no issues. I tossed the last bottle I had this past summer because it was wayyyy out of date.

... This may be a whole other thread but, I believe it was John Hall that I spoke to when buying stuff from him a couple years back that the gram strength of HHG has nothing to do with how strong the joint is rather how long the open time is. IOW 300 gels faster than 190 but in the end the joints are just as strong. I certainly could be mistaken and I wonder if anyone else here has hearrd this same thing.

Fwiw, out of maybe 30ish torrefied tops, I’ve def had a few do what yours looks like, with hide glue. I was using the lower strength hhg.

I switched to using titebond and haven’t had further problems. I scrape the finish all the way to the edges.

John told me the same thing on the phone the other day.

From the L.D. Davis site:

"The higher the gram strength, the stronger the cohesive forces in the glue. Cohesive forces are the attractive forces between the molecules in the glue, so as the gram strength gets higher, the glue will stick to itself better. The bond will also become more rigid as the gram strength increases."

Gram strength:

- Is an artifact of a specific test method and standard
- Is determined by how much force must be applied to a steel ball of specific diameter to penetrate a given distance into a standard gelatin sample (yes...it should be dyne strength in cgs, but no one expects measurement systems to be entirely rational)
- Does relate to how resistant to failure the glue line will be under load, as well as how rigid and resistant to deformation (but we have two other types of joint-related failures to worry about as well, so not the whole picture)

I would say that higher gram strength HHG is more resistant to wood movement-related glue line failures, dries faster, and is more resistant to failure due to high heat. Does that equate to higher strength? The glue manufacturers claim as discussed above - stiffer and internally stronger glue line - but like that 'stronger than the wood' business, other factors likely dominate ultimate strength of a joint, and seldom really matter for the joints we make in any case if the joint is a) durable, b) does not move, and c) can be made in conditions found in small craft shops.

What we saw at Greenridge:

- Zero failures of bridge properly made with 315g HHG
- Hundreds of failures of bridge joints glued with 192g HHG, fish, Titebond, and other AR/PVA (including both factory and custom instruments)...sometimes as a result of the joint design or workmanship, but too often just the joint giving way for no apparent reason
- Higher gel temps with increasing gram strength, with about 95 deg F for 192 g HHG and closer to 125-130 deg F for 315g HHG.
- Somewhat more difficult removal of bridges glued with 315g versus 192g HHG
- Reduced clamping time with 315g HHG - we loaded several bridges on quick turn-around repairs or test joints after just 3-4 hours with zero issues.
- Like other animal glues, no cold creep issues as seen with Titebond/thermoplastic glues and no hot releases on the unfortunate few guitars we've seen come back after automotive bake-offs.

That 315g HHG keeps the bridges on highly torrified tops is just icing on on the cake... Greenridge has been using 315g for all bridge joints since what appears to be 2009.