Glue Strength Question

[screamindaemon]

I have a question about glue. What kinds of glue do most people use? Is it really strong enough to hold a guitar together?

[CrazyManAndy]

Titebond, or other similar wood glue, is pretty common for most applications. Epoxy is also used. Hide-glue is used occasionally, but mostly for classical instruments.

And yes, it is strong enough to hold a guitar together. It better be, considering virtually every guitar (and most string-instruments in general) has been made using glue, though some use more than others.

CMA

Edited July 19, 2008 by CrazyManAndy

[Mattia]

Titebond - General glue-ups, kind of my 'go-to' glue for most things involving gluing wood to wood.

Hot hide glue - recently started using this, less difficult than I thought it would be (but make sure you have your 'dry run' working perfectly). Dries hard, no creep, use it for acoustics, mostly for bracing.

Epoxy - get good quality stuff. I use West Systems for general purpose gluing (things with lots of thin laminations, like neck-through blanks, and areas where moisture can warp things), have some 30 minute Z-poxy that I also use from time to time, and Z-Poxy finishing resin for pore filling. Place I always use it: gluing fingerboards, pore filling. Sometimes gluing carbon fibre to wood.

Superglue/Cyanoacrylate - thin, medium and thick, various purposes, mostly gluing bindings and doing inlay.

Polyurethane - occasional use in lamination (heel and endblocks for acoustics, sometimes headstock backstrap veneers, sometimes carbon fibre to wood lams, although I'm growing to like epoxy more as I gain experience using the good quality stuff. Makes a world of difference compared to dime store epoxy which doesn't cure as hard, mix as nicely or sand as well).

Fish glue - still testing, may use it in acoustics in places hot hide's working time is a pain (gluing plates to rims, for example)

[fryovanni]

I have a question about glue. What kinds of glue do most people use? Is it really strong enough to hold a guitar together?

What kinds- What Mattia and Andy listed.

Strong enough? The glue is not the weak link if the joint is made properly. The surrounding wood will fail well before the glue. Although if subjected to extream heat, moisture and such it will break down. If you subject a guitar to 160 degrees for a sustained period your going to get failures and the wood itself is not likely to fair well. Subject it to say 250-300 degrees for a relatively short period and you will break the glue down.

Rich

[screamindaemon]

Strong enough? The glue is not the weak link if the joint is made properly. The surrounding wood will fail well before the glue. Although if subjected to extream heat, moisture and such it will break down. If you subject a guitar to 160 degrees for a sustained period your going to get failures and the wood itself is not likely to fair well. Subject it to say 250-300 degrees for a relatively short period and you will break the glue down.

Hmm, maybe that is the explanation I'm looking for then. What constitutes a good joint? I've seen random pictures where a hole was drilled in both the wing and the main body and a peg was inserted to add to the joint. Is this what you mean? or are there other ways of creating strong joints?

[Setch]

A good joint means one which fits well, so that all surfaces are in contact, and no gaps or voids are present. For many joints on the guitar, which have lots of surface area (like a scarf joint or joint the in a two piece body) this simply means getting both surfaces perfectly flat and smooth, so that you get a very thin glue line.

Generally speaking, it's better to have a simple joint which fits pefectly, than to have a more complex joint with gaps. Glue itself is very weak, but the bond it creates between 2 pieces of wood is very strong. If you have a badly fitting joint you'll get a thick glueline, and a weak joint.

[zyonsdream]

I use a fine tuned jointer and planer to get solid joint and two types of glue

Good ol' fashion'd Elmer's woodworking glue for wings, tops and fretboards

And good ol' Crazy Glue for gluing frets into slots.

Both have always worked well for me.

[kpcrash]

I use a fine tuned jointer and planer to get solid joint and two types of glue

Good ol' fashion'd Elmer's woodworking glue for wings, tops and fretboards

And good ol' Crazy Glue for gluing frets into slots.

Both have always worked well for me.

ditto. Although I do break out the titebond occasionally, especially when doing a fabric finish.

[Narcissism]

you can buy all the above glues in almost sample sized packets. Try taking some of the scrap wood that you have left over, cut it in half with a motorized saw such as a jig saw or band saw, and then glue them back together. You can find out which glue you like the most that way. It may be a waste of time, but its a good way to verify for yourself that the glue you're trying out will work.

[Mickguard]

I've always had the feeling that 'wood glue' and 'Titebond' were pretty much the same thing, the latter being a brand name that, as brands tend to do, claims it is the best out there. But another glue with the same chemical formulation (since most wood glues share similar chemical formulations) will be equivalent. I use store brand wood glue, it works just fine (probably made in the same factory titebond has their glue made in anyway).

What wood glue does: it creates a secondary mesh of fibers among the fiber networks of the two pieces of wood. The glue penetrates the wood to a certain depth in order to create the bond. The glue's mesh is pretty strong --try to pick apart a dried up piece of glue --and the wood's fibers are strong mesh themselves (which is what makes wood solid). Combine the two and you've got a really strong bond.

But it's essential the there's a good join between the two pieces of wood (i.e., the greater the contact between the separate fiber networks of each piece of wood, the better the glue is able to form a 'bridge' between the two), and it's essential that the wood fibers are in the proper direction --it's why you can't get a good bond by gluing to end grain, because there's no similar mesh among the wood fibers there (since that is where the ends of the fibers are!).

At least, that's my simplified understanding of the process.

Meanwhile...

I cooked up a beef shank the other day -- I'd made the mistake of placing the shank with the flat edge of the bone to the bottom of the pot. The bone was apparently cut perfectly flat -- because it became glued to the bottom of the pot and could not be removed. I had to soak it for a couple of days before I was able to pry it off. Pretty impressive!

[Setch]

Not all woodglues are created equal, and the reason titebond is so popular is because it is a tried and tested product, and is widely available internationally. I have used a variety of different PVA/white/aliphatic etc glues for various woodworking projects, and they have different cure times, hardness, and handling properties.

IMO, not sticking with a known good product is a false economy, that's why I use titebond original for all luthiery work (unless I'm using a different type of glue ie: epoxy poly etc). I also like the fact I can identify how old titebond is, since it is date coded.

[fryovanni]

Strong enough? The glue is not the weak link if the joint is made properly. The surrounding wood will fail well before the glue. Although if subjected to extream heat, moisture and such it will break down. If you subject a guitar to 160 degrees for a sustained period your going to get failures and the wood itself is not likely to fair well. Subject it to say 250-300 degrees for a relatively short period and you will break the glue down.

Hmm, maybe that is the explanation I'm looking for then. What constitutes a good joint? I've seen random pictures where a hole was drilled in both the wing and the main body and a peg was inserted to add to the joint. Is this what you mean? or are there other ways of creating strong joints?

The idea behind using biscuts, dowels, scarf(angle cut joint), mortise & tenion, dovetail, finger etc... over a butt joint(flat square joint) is to develop more surface area for the glued joint(usually because the area to be joined would mainly consist of endgrain if it was butt jointed). Really what joint is best depends on the piece you are glueing, and the orientaion of the grain at the joint(you really want to avoid glueing end grain to end grain). On an acoustic you join the soundboard with a basic butt joint down the center of a two piece top, and the joint glueing surface will wind up being around 1/8" by about 20-21" long. That glue joint should not fail before the wood around it fails. To make sure this type of joint is perfect, you prepair the surface, then use a light source behind the joint and look at it closely. If you see any light you have not got the joint close enough. You can detect the smallest of gaps this way, extreamly accurate. When you prepair that joint you want to go ahead and glue it withing a few hours of doing so, because as the joint sets oils and what have you from the wood start to rise to the surface(creating possible contamination of your nice clean surface). That type of joint suits electric bodies, soundboards, archtop plates and the likes. In the case of a headstock joint, you wind up with a very small surface area, that is primarily end grain if you try a basic butt joint. This is where a different style joint such as a scarf is a good idea. You cut at an angle, this reduces the ratio of endgrain on the surfaces, increases the surface area, allowing for a stronger joint that can be straonger than the surrounding wood. Where the neck attaches to the body is another area that if you use a butt joint you are likely to have mostly endgrain to endgrain with very little surface. A scarf style joint is not practical, so other styles are used(dove tail, M&T most commonly). Mechanical joint(bolts or screws) is also viable and offeres a handful of advantages, along with a couple drawbacks.

Do a web search for any of the joints I have mentioned and you will get plenty of pics and examples. These have been used for hundreds(more likely thousands of years). They work, you just need to understand why, where, and what joint fits the needs of the application.

Rich

[soapbarstrat]

Mechanical joint(bolts or screws) is also viable and offeres a handful of advantages, along with a couple drawbacks.

What are the drawbacks ?

I finally saw how John Mayes bolts on the fretboard extension the other day (OLF), after having one of his videos for about a year, where he mentions it, but didn't show it (So I had thought he had concealed screw heads under dot inlays or something like that, but it's actually much better than that).

I use very little yellow wood glue with the guitar work I do, and I've only been buying small bottles of the Elmers stuff. When the bottles are almost empty, the remaining glue at the bottom of the bottle begins to dry. I then pull out the semi-dry blobs of glue (with a hooked piece of stiff wire and needle-nose pliers) and keep them to compare with other blobs from other bottles. After being out for months and fully dry, there are differences between samples from different bottles. Some pieces snap apart right away when I try to break them apart or crush with a vise or pliers jaws (I prefer this, since I think a brittle glue is probably less tone dampening). Other pieces bend like hard rubber and will not snap apart easily- actually very hard, if not impossible to snap apart. They have to be twisted and stretched to come apart (the fact that they *stretch*- yikes !)

I wonder if they add something to the glue to prolong it's shelf-life, and if this same additive compromises how well the glue works. Or in other words, I wonder if it's possible to have a yellow glue in a powder form, without the shelf-life prolonging additive (*If* there is any) and mixing small batches with water when you need some and having a better working glue.

Those more rubbery pieces are what make me wonder about this.

[bluesy]

Since we are discussing glues, I might mention that I have been told white PVA glues (not yellow like Titebond), as well as weakening at lower temperatures than the yellow, also have an age limitation. 10 years was quoted as the longest they might last before deteriorating. I am talking about the dried glue in a wood joint - not storage time in the bottle. This would be a worry as guitars should last a lot longer than 10 years

[soapbarstrat]

I only use white glue on carboard or paper. That's about as far as I trust the stuff. Also have prejudice against it, since we had to have a bottle of the stuff in our desk at school. I sometimes got in trouble on those days we were suppose to make craft stuff (stupid damn treacher trying to tell us we can't make fake guns in school !)

[fryovanni]

Mechanical joint(bolts or screws) is also viable and offeres a handful of advantages, along with a couple drawbacks.

What are the drawbacks ?

Drawbacks would depend on the application, but I am thinking about possible design issues (shape of parts, look of bolts or screws if visable, possibly added weight(more of an acoustic issue for weight nuts)). All mild issues(if they are even considered issues). The advantages are good for me. I use bolts for my acoustic necks, the inevatable reset will be much gentler on the guitar and easy to perform(that in and of itself is reason enough to sell me). I have NEVER noticed a functional difference.

Nothing I really need to mention as I am sure you know all the potential ins and outs of glued vs mechanical joints better than me.

On the subject of wood glues. I recall reading a post over at the OLF some time ago. It was by a member that actually had first hand knowledge of the differences in manufacturing some of the glue lines. He mentioned that there was a difference in the makeup of the glues. If I recall correctly it amounted to some consumer grade was a bit more watered down than the higher grade. Hard to understand why that would be when these glues are so darn cheap, but who knows what executives figure makes sense these days. I have a bottle of that LMI white that I have been using for a bit and it seems to be pretty nice(dries a bit harder than what I am used to with Titebond). Might be worth giving it a go next time your ready for a fresh bottle.

Peace,Rich

[dugg]

Hot Hide Glue all the way, even on electrics. HHG is the strongest and best sounding glue for instruments, it just takes time to learn how to use. Titebond loses a lot of water into the joint when it dries, leaving a 'lattice' of incomplete contact. HHG gels first, which leaves a solid area of contact. It's obvious with say, chair legs. The joint may loosen, but the HHG remains solid on one side of the wood, leaving a much better supported joint. Titebond would just crumble because it's not solid. Also, more importantly to the instrument builder, HHG dries hard as glass. Titebond is rubbery and dampens the sound. Another advantage of HHG is that you can use less clamping pressure, or none at all. This makes a finished instrument with less inbuilt tension. Violin makers know that instruments made with tension eventually relax, and their sound changes as a result. The goal of building an instrument without tension in the wood is that it doesn't need to be 'played in' as much.

[Prostheta]

Hot Hide Glue all the way, even on electrics. HHG is the strongest and best sounding glue for instruments, it just takes time to learn how to use. Titebond loses a lot of water into the joint when it dries, leaving a 'lattice' of incomplete contact. HHG gels first, which leaves a solid area of contact. It's obvious with say, chair legs. The joint may loosen, but the HHG remains solid on one side of the wood, leaving a much better supported joint. Titebond would just crumble because it's not solid. Also, more importantly to the instrument builder, HHG dries hard as glass. Titebond is rubbery and dampens the sound. Another advantage of HHG is that you can use less clamping pressure, or none at all. This makes a finished instrument with less inbuilt tension. Violin makers know that instruments made with tension eventually relax, and their sound changes as a result. The goal of building an instrument without tension in the wood is that it doesn't need to be 'played in' as much.

Rubbery and crumbly?

[fryovanni]

Hot Hide Glue all the way, even on electrics. HHG is the strongest and best sounding glue for instruments, it just takes time to learn how to use. Titebond loses a lot of water into the joint when it dries, leaving a 'lattice' of incomplete contact. HHG gels first, which leaves a solid area of contact. It's obvious with say, chair legs. The joint may loosen, but the HHG remains solid on one side of the wood, leaving a much better supported joint. Titebond would just crumble because it's not solid. Also, more importantly to the instrument builder, HHG dries hard as glass. Titebond is rubbery and dampens the sound. Another advantage of HHG is that you can use less clamping pressure, or none at all. This makes a finished instrument with less inbuilt tension. Violin makers know that instruments made with tension eventually relax, and their sound changes as a result. The goal of building an instrument without tension in the wood is that it doesn't need to be 'played in' as much.

HHG is great, but you read too much into the downsides of PVA(at least from my point of view). First forget that rubbery business, a properly made joint has VERY little titebond in the joint and makes a very strong bond. If titebond is fresh and cures well it is reasonably hard, not what I would call rubbery. The issue of creep over time certainly could have merit, but it would depend on the joint(the properly constructed joint between two halves of a solid body, not going to be on the chart as a potential issue). If there was a location where the issue of creep could register(and only "potentially") may be bracing on thin wood that is very active(soundboards or plates for example) although both glues have been used with success so it would be a theoretical issue. As far as water being introduced, HHG will intoduce as much water if not more to your build, you would really need to go with something more like Epoxy if you want to avoid introducing water.

I understand the concept of low tension building, and to me it is an issue of proper selection of wood and orientation of grain for the most part. Wood expands and contracts with moisture, and you are not stopping that from happening. The humidity control in your shop and moisture content of the wood is something you can try to select as the best "average" for where you anticipate the instrument will be used, but moisture levels will change. Trying to limit the introduction of moisture from adhesives or any other source is a reasonable goal, although there are limits to what is a sensable precation and what is going overboard(all depends on the application).

As far as HHG taking time to learn how to use. It is pretty damn easy to use really, although it can be a pain in the rear as much as a blessing. Titebond offers a simple, effective, simple to use on demand option that is very appealing. HHG does require speed and temperature considerations, but gives you fast cure rate and easy clean up as well as it is easy to dismantle and reasemble as it can be reactivated(pretty much an idiot proof glue, you screw up and you get plenty of easy do overs).

That is just my opinion, I guess I don't see the differences quite as night and day as you.

The goal of building an instrument without tension in the wood is that it doesn't need to be 'played in' as much.

There is also a popular school of acoustic building that believes building with tension, such as overdrying a soundboard prior to bracing and assembly, provides functional benifits as well as improves tolerance to changing humidity. It is kinda like the back is passive vs active schools of thought. Both have merits, but I think there is a sensable middle ground where the merits of these concepts blend to produce a nice durable and functional instrument. Absolute explanations tend to blind us to the subtle differences in these complex instruments, made from less than homogenous materials.

Rich