The real glue strength

[justrythym]

I hope some of the builders will chime in here. For days I have been reading post from here and everywhere else I can find. All I hear is how great hide glue is. I do believe it should be the glue of choice for instrument building. But what if your not interested in taking something back apart. What if you just want to make one shot do it? Nobody has ever said what the strongest and hardest glue is regardless of type or brand. That is what I would like to know. Everyone here seems to hate Titebond 3. I saw a very good glue test of several we all know including epoxy..... Elmers Wood Max And Titebond 3 were clearly leading them all in strength. It was hard for me to believe but I witnessed another different test with the same outcome. Everyone here has said that PVA’s are sound killers and to use only Hide Glue. I would just like to know how they could be that strong and no good for sound transfer. Thanks Guys! I enjoy so much reading the post’s from veteran builders here.

[Marty Jacobson]

Everyone here has said that PVA’s are sound killers and to use only Hide Glue. .

The #1 factor in glue joint strength is the quality of the mating surfaces. If you get true surfaces with .001" or less mating variation wherever you're gluing, whatever modern glue you use will be fine for a lifetime if the instrument is cared for reasonably.
Hide glue is strong, but brittle. The same thing that gives PVA a bad rap is what makes it resilient. There are pros and cons. Some impacts would be better absorbed by PVA, other stresses by HHG. You can't design for everything.

[rcc56]

I just pulled the back on a guitar assembled with white PVA. It took a long time. Hide glue would have been easier to open.

PVA glues creep and can turn to mush if they sit in heat over 105 - 110 F for only a few minutes. Hide glue doesn't creep, and can stand more heat. It's also the only glue I know of suitable for instrument construction that sticks reasonably well to itself.

If a glue joint made with Titebond or white PVA fails, and is difficult or impractical to clean [such as a loose brace or tone bar], the strength of the joint will be significantly compromised.

Non-reversible glues are fine if you never intend to repair an instrument. Problem is that most instruments will need to be repaired sooner or later.

Hide glue and Titebond Original have both proven themselves well. Both have their attributes and drawbacks. The longer I work on instruments, the more I prefer hide glue, especially on older instruments.

[kjbllc]

if you are doing something that is never to be taken apart , then other glues ok, as stated above . the last thing I saw on glue strength was titebond 1 is the strongest , but for some things good old elmers is good

[ProfChris]

The tested "strength" of a glue joint is usually pretty irrelevant. With good mating surfaces, what normally fails is the wood itself rather than the glue line coming apart.

For instrument building, far more important are the potential failure modes of a glue joint and its repairability and usability for that application.

Failure modes:

1. Impact - If you want to resist this then brittle glues are not for you. Sledge runners might be an example.

2. Heat - PVAs, Titebond, even epoxy tend to soften with heat, and re-set afterwards. This is a known problem with instruments left in hot cars, which can come out a different shape!

3. Cold creep - if the stresses are trying to slide the glue line sideways, PVAs and Titebond can allow this over time. Hide glue doesn't. I don't know about epoxy, I suspect different formulations behave differently.

Repairability and usability:

1. Hide glue is the only (so far as I know) easy glue for disassembly and reassembly, because fresh glue reactivates the old glue.

2. Working time is important - hide glue gives you seconds, maybe a minute or two if the parts are heated. But it reactivates with heat and moisture, so I like it for assembling bodies because I can finesse any slight gaps.

3. Moisture and wood movement. Fingerboards tend to curl up from moisture in glue (not good), so some people prefer epoxy for these joints.

4. Wicking into gaps - CA glue is especially good at this, helpful for lifting frets, plastic binding, etc.

And so on, and so on ...

Each builder finds the combination of glues which fits with how they like to work, so there is no consistency. If I could only ever use one glue I guess it would be hot hide glue, though Titebond Original would also be an option.

I'd say there is one consistency though - strength of glue joint is rarely a consideration in choosing glue (excepting Pritt stick and flour and water paste, though I've read that rice flour paste is used in some Japanese woodworking!).

[Richard500]

Non-builder here. One of the considerations not mentioned so far is that glue strength can be too much. HHG, in particular, comes in different ‘strength’ formulations and I have read that where it might be an issue, a glue that is too strong will tear apart the wood parts if something like an instrument is subjected to high stress from, say, temperature or humidity or string tension. Or, for repair purposes, if you need to separate a joint, (cold), you want the glue to rip before the wood.
If my 300 pound neighbor crushes my ladderback chair, I would like the tenons to pull out rather than break off.

[Mike Sayre]

Fish glue has been the subject of Stew Mac videos beginning I think only a year or two ago. Opinions on that?

[rcc56]

Fish glue has a poor reputation, due to failure in high humidity conditions. While some of these failures may or may not be due to operator error, I prefer not to use it.

Here is a recipe for hide glue with increased open time: 10 grams water; 5 g. hide glue flakes, 190 to 215 grade; 0.5 g. urea. If you want a thicker glue, you can reduce the water to 9 g. It can be thinned later if necessary. Note: this is not a "liquid hide glue." It must be used hot. Urea can be purchased from an artist's supply store.

I will use it in repair work when I need increased open time to set clamps and jacks, such as regluing loose guitar braces.
This glue is practical only on joints that are new, or previously glued with hide glue. If something else was used previously, you must first clean out all of the old glue.

Necks, fingerboards, bridges, and body joints get pure hide glue. You get used to laying out your work, making a dry run, and working quickly. A hair dryer can be used to pre-warm gluing surfaces.

[justrythym]

We right away started talking about repair again. Once more let me be clear........I am talking only of strength. If you were hanging 500 feet off the ground with nothing but a wood to wood joint between you and the ground! WHAT GLUE WOULD YOU CHOOSE? Let me explain.... I have a compromised neck joint on an F-5. The joint is clean. The neck is not great. If the joint fails it will have a new neck built for it (period). I will remove the old neck in pieces if need be. I just want it to have the best chance at holding. Is there a informed educated answer here? Thx. Appreciated

[Jeff Mando]

FWIW, I'm a repairman, not a builder or an "artist" at all. For me, original Titebond works for 99% of what I do. To be honest, I'm not fast enough for hide glue. Original Titebond will give you about 20 minutes or more to clean up all your squeeze out, something I try to be meticulous about.

Superglue is also handy for things not requiring structural strength and quickness.

Epoxy is used once or twice a year as a last resort when other repair attempts have failed, but it is much harder to work with and requires acetone for cleanup, which pretty much ruins most finishes, so you really have to plan ahead, mask, etc....no fun.

[rcc56]

Re-gluing or replacing a neck is a repair.

The only glues I use for neck joints are hot hide glue or Titebond Original. They are both well proven. Clean the joint again very well before gluing. Bear in mind that Titebond may creep, while hide glue will not. If the joint does not fit tightly, you must insert a shim or graft in new wood, and re-fit tightly.

If the joint is a butt joint or a non-dovetail mortise and tenon, no glue that I know of can be considered 100% reliable.

I suggest you spend some time browsing Frank Ford's excellent website, frets.com. They have a fine article on glues, and many on myriad aspects of repair.

[sunburst]

...If you were hanging 500 feet off the ground with nothing but a wood to wood joint between you and the ground! WHAT GLUE WOULD YOU CHOOSE?...

What is the joint? Lap joint? Butt joint? Other?
What are the conditions? Hot? Cold? Wet and rainy? Indoors/outdoors?
How was the joint prepared? Well fit glue surfaces or some gaps?
How long will I be hanging there? Minutes? Hours? Days? Years?

No single glue or adhesive is best for all different situations. Some have greater tensile strength and poorer sheer strength and vise versa, some have better moisture resistance, some fill gaps better, some resist heat better, etc. etc..

[justrythym]

Neck joint repair. Dovetail was broken. Now joint is more of a MT joint. Joint is fairly snug with a small gap. There has been a hold drilled through the neck block into the heel. There will be a screw inserted with access from the end pin hole at the time this is all glued up. The fretboard is off at this time as well as the fretboard support. Will install fretboard with liquid hide glue. What should I use on the neck joint? Again....not worried about future take down or repair.

[Bill McCall]

We right away started talking about repair again. Once more let me be clear........I am talking only of strength. If you were hanging 500 feet off the ground with nothing but a wood to wood joint between you and the ground! WHAT GLUE WOULD YOU CHOOSE? Let me explain.... I have a compromised neck joint on an F-5. The joint is clean. The neck is not great. If the joint fails it will have a new neck built for it (period). I will remove the old neck in pieces if need be. I just want it to have the best chance at holding. Is there a informed educated answer here? Thx. Appreciated

Joint prep is the big issue, all of the glues mentioned will provide adequate service. Hide glue, for example, has been used for hundreds of years and its track record is quite good. Poor preparation won't enhance the service of the strongest adhesive.

If your repair requires the 'world's strongest glue', perhaps a more seasoned person is right for the job.

[sunburst]

Neck joint repair. Dovetail was broken. Now joint is more of a MT joint. Joint is fairly snug with a small gap. There has been a hold drilled through the neck block into the heel. There will be a screw inserted with access from the end pin hole at the time this is all glued up. The fretboard is off at this time as well as the fretboard support. Will install fretboard with liquid hide glue. What should I use on the neck joint? Again....not worried about future take down or repair.

What is the value of the instrument?
Sounds like a poor joint no matter what; a ruined dovetail made into a more-or-less straight mortise and tenon with gaps (poor fit). If the instrument value is low and it will never be subject to repair again, that sounds like a job for epoxy. Epoxy is among the best for gap filling and holding poor joints and butt joints. It cannot be considered reversible in a neck joint, so once it is done there's no going back (hence the instrument value rhetorical question).

[justrythym]

John, was hoping you would give me your thoughts. I posted a more clear description of what the joint in question is. Let me say this and it may help. I will not use regular hide glue here. I do not feel comfortable with it. With that said, will there be any difference in sound transfer and strength of what I have to choose from? Thx.

[sunburst]

As for "sound transfer", that is really not a concern. I believe we would not hear a difference no matter what glue is used.

[justrythym]

I understand fully on the ability to do this repair over. I actually at first thought about JB Weld. Is that a foolish thought, all things considered? The screw will add strength as well IÂ’m sure. Everyone should watch the results from the test I spoke about earlier in the post. TB3 and Elmers Max was very very impressive in terms of strength. Actually Elmers Max beat them all out in terms of joint strength. It surprised me.

[sunburst]

I understand fully on the ability to do this repair over. I actually at first thought about JB Weld. Is that a foolish thought, all things considered? The screw will add strength as well IÂ’m sure. Everyone should watch the results from the test I spoke about earlier in the post. TB3 and Elmers Max was very very impressive in terms of strength. Actually Elmers Max beat them all out in terms of joint strength. It surprised me.

JB Weld is simply epoxy with metal powder mixed in (probably a little more complicated than that in reality). Plain ol' epoxy is about the same in a wood joint.

As for the glue test; how many types of joints were tested? Were the glues tested for tensile strength, sheer strength, shock resistance etc. or was it just a simple one-type test to failure? Did they test under different conditions of temperature? Humidity? Test for creep under constant strain? In short, simple glue tests almost always don't tell us all we need to know when it comes to choosing glues and adhesives for jobs. If a glue is strong enough for our application, stronger is not necessarily better, so choosing glues with characteristics well suited for our application is much more important.

[justrythym]

Thanks Man! For the record?....this joint is not really as sloppy as it sounds. Top was crushed in, dovetail broken, rear block broken too. My Son bought this for me to repair. I put a red spruce top on it and itÂ’s ready for the neck. The neck is quite thin. If the joint fails IÂ’m going to just put a new neck from scratch on it. Thus the question of the one time strength deal.

[Richard500]

Still confused here. Can anyone explain why the neck joint has anything acoustic going on, or why a nice solid nut and bolt would be inappropriate on a salvage job?
If cosmetics matter, recess the bolt head and cap it with a dowel. Or use a wood anchor for machine bolt, as in furniture.
“On the Venus de Milo, an engineer discoursed ‘why the damn thing’s only concrete, and should be reinforced’”

[sunburst]

...Can anyone explain why the neck joint has anything acoustic going on, or why a nice solid nut and bolt would be inappropriate on a salvage job?

No.

[rcc56]

My sole objection to a well designed bolt-on neck is inserting or removing the bolt on an f-hole instrument.
Not my idea of a good time.

[Bob Clark]

My sole objection to a well designed bolt-on neck is inserting or removing the bolt on an f-hole instrument.
Not my idea of a good time.

So you would not object to one on an oval-hole instrument? Good to know. That is the conclusion I came to as well.

[rcc56]

No, I would not object at all, as long as it was well designed.

When the dowelled-on neck pulled loose on my Octofone, I re-installed it with a bolt.

I don't think I would install a bolt on a vintage Gibson or Martin instrument. I don't believe it would change the sound or structural integrity, and it would make future repairs easier. But the purists and even the not-so-purists would have a fit.