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I have distilled water in the house for other reasons, so I also use it for hide glue. One less thing that can go wrong.

I've used both tap water and de-ionised water (sold for car batteries)
If there was a difference, I didn't notice it.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I had never considered the usage of 315 strength hhg for attaching bridges on repair instruments. This was a timely recommendation. It is sort of a freak occurrence that I have 3 '70s era Martins in my shop currently that are undergoing extensive work including reattaching bridges on patches that range from bad to worse. I have been worried about getting maximum wood to wood contact but that is problematic on one guitar that has had its bridge reglued once before. I have leveled it as much as I could but removing more wood to get it truly level would leave too deep of a pocket. So I am attempting to come up with a method to shape the bottom of the bridge to fit the slightly undulating bridge patch. Chalk fitting doesn't seem to work since I can't rub the parts together to transfer the chalk due to the finish pocket. I have come up with a possible method to floss this joint and will show some details if it works. But for now, I have some 315 strength hhg on order to assist these projects. Thanks Woodie!

Has anyone experimented with mixing the hide glue with 10% acetic acid 40%? That should extend the open time significantly and also make the glue 20 % stronger.

I heat the HHG to 50 degrees C, a bit less heat than the recommended 60 C. This keeps the strength of the glue better, if you overheat it or heat it for a long time the strength will decline. I always preheat the wood with a pretty hot (250-300 degrees C) heat gun and I have plenty of time to do gluing of fretboards and bridges. The glue I'm using (http://www.tanex.cz/en/produkty/hide-gl ... ecial.html) have a gel rigidity of 300, it's a great glue.

Lately, I have started to use two sets of HHG when gluing bridges. One regular blend made of 3 volume parts water and 2 parts glue grain, and one little bottle where I dilute the regular glue with 50% additional water. The idea is to use the diluted glue first to get a good soak deeper into the wood, and then wipe away the excess before using the regular HHG. The regular glue will then bond with the thinned down glue that goes deeper into the wood.

When I use diluted hot hide glue on the underside of a fretboard or bridge, I can clearly see patches where the glue is dried out from soaking into the wood. In that case, I add some more glue until it doesn't dry out. The diluted glue can be reheated to liquid again if needed with the heat gun before the final gluing.

I use 10% urea (volume or weigh of the glue and urea grain) to get longer set time when gluing the bottom to the rim.

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New will change the old,
turn to ashes or gold

http://www.gammelgura.se

We don't have any problems making regular strength... HHG work for all we do which is considerable with our annual volume of repaired instruments.

We've developed methodologies to say for example have all clamps in place prior for bridge gluing where we can have a bridge in place and the clamps snugged reliably in 10 seconds or less every time. This is just one example of working within the constraints of the glue not trying to make it do unnatural acts to conform to how fast we can work.

Not trying to be argumentative (glue thread...) and do whatever the hell you want with your glue that's up to you but I do want to represent an opinion here that with thought and care regular HHG can do all that we need it to do and has done so for thousands of repairs that we have done out of our shop.

This does not require a degree in chemistry.

Just respect the open time, do dry runs, understand the relationships with RH and temp and proper curing, have woodworking chops when it comes to well fit joints and HHG is a wonderful thing, as is.

I thought acetic acid was used to soften glues - ?

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

. . . and my response, as it has been before, is that there is nothing “unnatural” about adding some urea to hot hide glue to extend its open time. People have done it for a long time, and it is an established way to accomplish a specific goal. It should not be a taboo. It’s a choice, with it’s own set of goods and bads, as is the choice to not add urea. I respect the choice not to use it, but buck against the notion that those who do choose to use it are doing something wrong. They aren’t; they are just making a choice.

Acetic acid added to HHG is not what I would call a natural use of HHG and it was mostly what was on my mind with my comment.

My interest here is to hopefully distill some of our practices into something that promotes what we do and how we do it and offers safe, sound advice for new builders which is what most people here are. I want people to not be afraid of HHG and worry about urea and how much and acidic acid and the handling of that.

Nope, no need to die on this hill Don (or Hesh) I'm simply promoting a wonderful thing, HHG as is, used properly and greatly appreciated.

FYI for everyone else and you Don Mario has a wonderful video of him gluing on a plate with HHG. Not an application for the faint at heart with HHG's short open time but Mario's approach is brilliant. Since the additives that people mention are generally, generally to extend open time this is a direct example of where more open time would be helpful but you can work around it as this world-class builder surely does.

No urea, no additives of any kind in fact the only thing he did different was a bit less water. By making the HHG more viscous it creates a "bead" when put down that the outer layers of the bead start to jell and then protect the inner layers of the glue from rapid cooling off. When he smashed/placed the plate on with the clamps the bead is of course broken, the glue squeezes out and then with the use of a heat gun he reactivates and sets clamps. Makes it look easy and it is how he does it but a lot of thought within the parameters of proper HHG use went into this method and he accomplishes a difficult and not typical HHG task that was very impressive to many of us.

It's also an example of where some would use additives and Mario didn't.

Lastly if you have not tried HHG it's easy, safe and a great glue, give it a try it need not be complicated or scary.

I'm not finding Mario's HHG plate video if anyone has a link please post, thanks.

https://www.youtube.com/watch?v=y2SuYAYJ5oQ


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Hello Hesh, which glue would you prefer for laminating a neck? and for wooden binding? And would you please explain to me what 192gr or 315gr mean? Bloom gramms?

I think it´s a good idea to have hide glue with different additives for different tasks. Urea and acetic acid are very long known additives to get more open time before geling, and potash alum is a very long known additive to make hide glue waterresistant. In europe.

Does everyone here uses StewMac hide glue? Here in Germany there is a factory that produces different glues, even six different types of hide glue!

Thanks Brad, this is it and killer tunes playing too. An excellent example of zero additives employed for a long open task with HHG.

Hello Juergen. Google is your friend for some of your questions such as the gram strength question.

My interest and my meaning for this thread is that 192 is a general purpose HHG and it has longer open time than 315 or the 250ish variety. For folks who use rub joints short open time is desirable. For what we use HHG for often such as gluing on a bridge on a steel string with twice the string tension of a classical a short open time is not desirable and instead a more penetrating, longer open time is a better way to go. Roger touched on this in his post about thinning HHG, a great technique for better penetration and often used by us on head stock break repairs.

Instead of giving you my recommendations for what glue for what application I'm informed by the application and my own beliefs about the value of HHG. For example the crystalline, hard nature of the glue makes it excellent for transmitting vibration. Softening the glue, using additives such as what we see in bottled hide glue in the states really turns it into a different glue with different qualities stemming from how hard it cures.

I found Titebond original great for long open time, non-acoustically-critical applications such as neck laminations and fret boards. What I advise people to avoid is don't use a short open glue on a long open task or it may fail. I also advise people to avoid any glue or technique that your dry runs did not produce success in the time allotted.

For wood bindings the only bindings I ever used I used Titebond original too and never lost a binding.

I did use HHG for necks (attachment to the body), bridges, bridge plates, all braces, some center seams but in hindsight it wasn't necessary. Pretty much anything that generated or transferred vibration I tried to use 191 HHG.

Our HHG comes from LMI (the last batch) which is US manufactured and high quality 191 glue. Like the video we have adopted our methods and honed our chops instead of adding things to the glue to match our work speed. We believe in our approach and recommend it especially to newer builders who need a break with clear, simple advice that stands the test of time.

A different perspective is that having the glue gel before the parts are placed is very frustrating. So, a person who is geared up for working with hot hide glue can just add a smidge of urea in order to add a little extra time and run less risk of the glue gelling before the parts are placed. I don’t add urea when gluing bridges, because there is no need. I have glued back and tops on with hot hide glue without using urea, but you really have to hustle to get it done. Adding a little urea for those jobs that take longer doesn’t hurt the strength of the glue, but it does help avoid gelling too soon, which is a good thing.

I use hot hide glue for literally 100% of what goes on a guitar. This way, there is no mystery in the future as to what adhesives I used where. When you mix your glue for the specific task at hand, it’s easy to optimize the glue for that task. So, I wind up working with hot hide glue a lot. It can do way more than others use it for.

My overall point is that there is not an orthodoxy regarding glues (or, rather, there should not be). Different people make different choices. If a person is ready to use hot hide glue, they are likewise ready to consider additives, if they want to. Some really great guitar makers and repair people use additives. It’s just a choice.

No hill deaths here, Hesh. Just providing a different perspective, one that does not consider an additive like urea as a bad thing to be avoided.

Actually, there is somewhat of an - orthodoxy - regarding using glues. Without one you will have many more failures. Not only the right glue, but also the right way to use it are important for quality work. It does include using urea with hide glue in relatively small amounts, and perhaps acetic acid, which I have used to soften dried hide glue.
Here is an interesting FAQ by Craig Deller which I found on the David Van Edwards site. It mentions using acetic acid to improve the "wetting" qualities of HHG - I learn something new every day (Thanks Juergen!).
https://www.vanedwards.co.uk/glue.htm

Has anyone tried mixing different gram strength glues (192 -315) to create something in between? Would that work?

Clay—

To me, there is a difference between these two things:

1. A person understanding the properties of the adhesives they use, and using that knowledge to make good choices.

2. An individual or group declaring, based on their own views (which are not perfect, despite good intentions), what adhesives everyone should use in which situations, and describing deviation from those guidelines as wrong, despite the obvious fact that others have success doing things that are counter to those declarations, probably using the knowledge referenced above.

I consider the second to be an orthodoxy, a set of rules that are overly restrictive. I consider the first to just be good sense, and that is (to me) what you have described.

As I said above, there is not (or should not be) an orthodoxy in guitar building as to which glues should be used where. But there is knowledge to be had regarding how different glues work. I encourage everyone to gain that type of knowledge, particularly about hide glue, because it is wonderfully versatile stuff.

Yes, I do that. I mix192 and 315 to get (hypothetically) around 250. I don't remember the proportions off the top of my head but I calculated it by weight. My rationale is my WAG that the gram strength of the glue is directly proportional to the amount of protein in it. If true, mixing would make sense to me. If not true, uh ... dunno.

My experience with HHG is minimal though. Right now I am psyching myself up to fix a failure of detached X-brace arms in the lower bout of a guitar I made last year, my first attempt to use HHG for braces (with vacuum clamping). My recollection is a little fuzzy but I think I used straight 192 for that. Whichever glue it was, I'm pretty darned sure that failure was due to technique, not glue properties but I guess I can't guarantee it. Other glue joints with my mixed glue are definitely holding up well a year later.

I used them all remember that the strength also means the viscosity . I use 192 as it has more open time and heating helps. The higher the gram strength the faster it gels. 192 and 251 are plenty strong enough in that they are stranger than the wood. The big thing to know is that they don't gap fill well as tite bond does.
Make your joints fit clean and proper clamping. Most failures I see are from poor jointing technique. Not to the wood is #1 working to slow and glue gels before clamping.
work efficiently you can heat a bridge with a hair dryer and we are not talking HOT we are talking body temp or under 100 degrees. I have seen posts that recommended using salt to keep things from moving DO NOT DO IT salt weakens the glues so practice your clamping procedure and you should be good to go

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Salt is one of the additives like Urea used in HHG to extend the open time. I have tested it and while not quite scientific the wood always broke before the glue line.

I short article I posted advised against adding salt or urea to hide glue used for instrument making. I wonder if these additives might add to the hygroscopic nature of hide glue and make it behave more like fish glue, which some have reported to fail in high humidity environments?
It also mentioned a couple of things you can do to make hide glue waterproof. I wonder how well these actually work - might be interesting to try on glued up neck blocks.

Regarding the use of urea (in modest amounts), I put more faith in these sources:

1. Frank Ford and Don Macrostie, who wrote an excellent article for AL some time ago, in which they mention using urea to lengthen pre-gel time. They say modest amounts do not adversely affect the glue.
2. My own experience with adding urea to hot hide glue, which has been positive.
3. The fact that people successfully use Old Brown Glue to make instruments, and that stuff has way more urea in it than I normally use.

There is a lot of “lore” in instrument making that doesn’t get backed up by something substantial, and I put the “don’t use additives” boogeyman in that category. People way smarter and more experienced than I am have a history of using urea to extend pre-gel time, and my own experience with it has been great. Those things outweigh the contrary view, for me.

Hi Don,
As they say.... consider the source. The individuals you mentioned have a good reputation in the repair field, and far be it from me to criticize them (do they add urea when gluing bridges?) What some may feel is a prudent admonition others might find too restrictive. Would you build an instrument using old brown glue? I think one well known builder used superglue exclusively to build a guitar.
I find it interesting to consider viewpoints other than my own, and at times they have modified my understanding of things. I try not to be too dogmatic, and think about why others may feel differently than myself about something. I might piss in the glue pot if I felt I needed more open time for some gluing operation I didn't think I could do without it, but so far that has not been the case. It is good to know that adding urea has worked well for you and others without detriment to the final result.

Clay—

In answer to the question “would you build an instrument from old brown glue” (I won’t treat it as rhetorical), I could if I had to, but I don’t have to, so I don’t. There are gluing tasks where I far prefer the normal gel time of untreated hot hide glue. The glue gels quicker (obviously) without urea, but it also dries quicker, and gets to the point where clamps can be removed quicker. Old Brown Glue would slow me down a lot of the time, and it is expensive, compared to making your own version of it. But yeah, I think it is strong enough to hold a guitar together. Of course, the ideal for me is using less urea than is needed to make the glue liquid at room temperature. I like slowing down the gel time a little, not eliminating it. And only for certain tasks, the ones where it is not easy to get everything in place before gelling occurs. There aren’t many of those. My use of urea is conservative, really. As I mentioned before, I don’t need it for bridges. I have no idea what Frank Ford and Don Macrostie use it for.

It may be useful to mention that I cook fresh, small amounts (less than 3 fluid ounces) of hot hide glue every time I need to use it, rather than the whole “it’s glue cooking day” approach of making a lot and freezing it. To each their own, but a big benefit of my approach is that I get to formulate each small batch for the task at hand. Sometimes I need thicker glue; sometimes I need thinner glue. Sometimes I want to extend pre-gel time; sometimes (most of the time, actually) I don’t. I like this freedom to tailor the glue to the task.

While the peeing in the pot idea is probably the genesis of the use of urea, it is (thankfully) not how one does it these days. There are little BB sized pellets of white stuff you put in the brewed glue. It’s all very clinical now.

I agree with considering many viewpoints; that’s the overall point I’m trying to convey. Different ways of doing things (like how to formulate glue) are just choices. I love varied choices. With good knowledge of how things work, one can make great choices that others would not consider their cup of tea. That type of variety is a good thing.

I have different hide glues, from 60 - 120 gr Bloom up to 430 gr Bloom. Yesterday I received acetic acid 40%, urea and potash alum. During the next week I will make glues with different Bloom gramms and different additives and test the open time and the overall strength. As soon as I get results I will post them.