Official Luthiers Forum!

I’ve read on this forum and several other place that some folks are adding salt to their hide glue. What are your experiences with this? I understand they are doing to extend gluing time but does it negatively affect the strength?

John--

I don't use salt, but I do use urea for the same purpose: to extend the time that the glue remains liquid. From what I have experienced, a person can add urea in an amount that is about 5-10% of the weight of the dry glue used to make the batch and not really notice anything different about the glue, other than it stays liquid a bit longer (plenty long enough to get the clamps onto a complicated glue-up). If you add urea in an amount that is about 30% of the weight of the dry glue used to make the batch, that gets you into the territory of hide glue that stays liquid at room temperature, like Old Brown Glue. Other than that obvious difference, the differences I notice in the glue when I add that much urea are that the glue takes a lot longer to fully dry, and it often stay a bit rubbery in texture, whereas hide glue without that much urea is very rigid when it fully dries. I have not done any strength tests, but a lot of people use Old Brown Glue and are happy with it. I prefer the properties of regular hot hide glue, unless I know a glue-up is going to take a very long time, like when I glue together purfling parts.

I know there are folks who use salt on the OLF. They will probably chime in.

I've used both a little salt or urea to extend the working time like Don talks about without negative effect.
You might have a look at this; https://www.violins.ca/forums/viewtopic.php?t=1441 . There is post by Mat Roop, post 9 I think with some information from Eugene Thordahl of Bjorn industries (hide glue supplier) that would probably address your question.
I would make up a few batches of various mixtures and test it out on scraps.
I think getting too thin a mix would much worse than adding a little salt or urea as far as joint strength goes.
Also - Old Brown Glue works well for a lot of task, like binding for example, or mix a little with your own fresh HHG to extend the working time a little.

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Jim Watts
http://jameswattsguitars.com

This is pretty much what I do now except for a few operations like dentalones which I like the faster tack HHG. I add enough salt so that the extend time is longer but it is not liquid at room temperature. It still goes in a 145 deg water bath. I mix up the glue then put it in litte glue bottles with a couple stainless steel nuts in it for weight. The glue bottle is dropped in the water bath and since it has a cap the water doesn't come out of the glue and thicken up either. At the end of the day I put the bottle in the refrigerator.

What is your mix ratio for glue, salt, & water? Is this ordinary table salt?

I wouldn't do it. If you need to extend the open time of HHG consider using a different glue that you can 100% comply with it's requirements, all of them.

HHG is not the magic bullet to a superior instrument. It is however a favored and excellent club to have in your golf bag.....

Following doncaparker's posts, I've been using 7% Urea in my HHG and like working with 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.

That feels like a non sequitur, Hesh, which makes me think there is something else in your thought process that the rest of us haven’t caught up to yet. Going completely without urea or salt (to extend working time) is not one of hot hide glue’s requirements. Really serious users of hot hide glue, like those who do museum restoration work, use additives like salt and urea. I don’t know of any good reason to refrain from using it, in appropriate amounts, when it is what makes a particular job easier to complete successfully.

I’ll speculate and say that you may be focused on the use of hot hide glue for gluing on the bridge. If that is true, I agree with the idea that urea or salt is not needed, and if it is not needed, then a person is better off not using it. But these additives (in appropriate amounts) make a number of other gluing operations easier, so I take advantage of that. I encourage others to do the same. It is a very versatile adhesive, when you can tailor the mixture to what you need in the moment.

Yeah I don’t think I would feel comfortable using any modified hide glue on bridges, bracing, or linings. I do however think I might consider a salted version of HHG for gluing back plates on, for whatever reason I struggle with time on that. I guess I wonder what does salt or urea do to negativity affect the glue does it weaken it significantly or cause excessive moisture absorption over time?

The stainless steel bolts are a great idea, thanks!


Pierre
Guitares Torvisse

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Pierre Castonguay

We use HHG where it makes sense to do so where a crystalline, rock hard cured glue that can be serviced in time makes sense. It does not make sense to use HHG on side supports or a nut or the fret board or, or, or. It does make sense to use it on braces, bridges, bridge plates, etc. I would also add that joining plates with HHG can be problematic when the builder does not understand how plate joining is supposed to work and uses HHG because they read somewhere while sitting on the pot that it will pull the two substrates together so they thought it was better for a poorly prepared joint.

If this was a forum full of accomplished builders with lots of instruments under their belts I would not be concerned about people following the requirements for use of HHG. OTOH my experience with many of you here, direct, in person experience informs me that someone should say that there are alternatives to HHG if you do not have the chops, tools, knowledge or time to use HHG correctly.

Do you know that we have had to reglue several bridges for OLFers where they used HHG and the bridges lifted? Not naming names they are my customers now but it has happened frequently enough that we are concerned that some are using HHG without fully understanding it.

I'll take my HHG straight up please and be happy to pocket the fee for regluing someone's poorly installed bridge when they attempt to make HHG use meet their requirements in terms of open time instead of respecting HHG's requirements for proper use. But for the record why go there? If you cannot complete a glue-up operation in the required time for HHG use something else.

Many of us use stainless bolts or nuts in our HHG bottles because Mario P. posted this idea back around 2007 and we all ate up what ever he shared. My empty HHG bottles are clean and in a drawer and each one has a stainless bolt in it.

Hesh--

Is John (the OP, moniker: Slim) one of the builders whose instruments you have had to repair due to his bad decision making and/or lack of skill?

If the answer is no, then it would be better if you did not assume that he makes bad decisions, or lacks necessary skills. In other words, it would be better if you did not project onto the OP (or anyone else, without a factual basis) the negative stuff you see in your profession as a repairer of instruments. Not all of us commit the sins that land in your shop.

It would also be better if you did not depict the use of salt (or urea) to extend the working time of hot hide glue as a mistake. It's not a mistake; it's a choice. Ask Frank Ford or Don MacRostie or Patrick Edwards (the Old Brown Glue guy). The fact that you make different choices does not make this choice objectively wrong.

Can a person mess up with hot hide glue? Sure, the same way they can mess up 1,000 other things that go into making a guitar. The answer to that problem is not the avoidance of all things that can be challenging; rather, the answer is the cultivation of good skills and good judgment.

You know that I highly value your opinions, and most times I consider your opinions as the gold standard. I think you also know that I won't be shy about telling you when, on the rare occasion, I find your compass to be pointing somewhere other than magnetic north. This is one of those times.

I can 100% confirm Hesh does not have any acoustic instrument made by me. Well I guess I ask the question based off the fact I thought it might be handy to have the ability to mix a small batch of hide glue with extended working time for special situations without having to mess with heat gun or heating lamps. Also what stirred me to ask was I read a write up from the Eastern Massachusetts Guild of Wood Workers in it the author gives extended work time hide glue recipe based off of info provided by the Animal Glue Industry whatever that is.

https://emgw.org/resources/Documents/Me ... andout.pdf

The reversibility of hide glue, how it sands, how it takes color, & how hard it gets is what I like. I know some will say just stock some fish glue or order some liquid form of hide glue, but why if you already have HHG and salt if it can work? That’s what I’m asking does it work & your experience good, bad, or ugly. Also

Thanks for the link Slim. The vinegar as an additive looks interesting, possibly for torrified spruce.
I've only recently started using HHG, so really don't have the experience to offer.

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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 have no experience with any of the suggestions made in the link I provided, I did however mix a small batch of the so called shop glue and glued a couple of sticks together to see what happens. I would caution anyone to experiment thoroughly before committing these mixtures to a build I know these mixtures will not be replacing the role of HHG in my builds at this time but I might learn something along the way experimenting on other wood work. After all isn’t that is what it’s all about is learning!

Don I'm quoting you below because the forum software would not let me embed three quotes:
Hesh--

"Is John (the OP, moniker: Slim) one of the builders whose instruments you have had to repair due to his bad decision making and/or lack of skill?

If the answer is no, then it would be better if you did not assume that he makes bad decisions, or lacks necessary skills. In other words, it would be better if you did not project onto the OP (or anyone else, without a factual basis) the negative stuff you see in your profession as a repairer of instruments. Not all of us commit the sins that land in your shop.

It would also be better if you did not depict the use of salt (or urea) to extend the working time of hot hide glue as a mistake. It's not a mistake; it's a choice. Ask Frank Ford or Don MacRostie or Patrick Edwards (the Old Brown Glue guy). The fact that you make different choices does not make this choice objectively wrong.

Can a person mess up with hot hide glue? Sure, the same way they can mess up 1,000 other things that go into making a guitar. The answer to that problem is not the avoidance of all things that can be challenging; rather, the answer is the cultivation of good skills and good judgment.

You know that I highly value your opinions, and most times I consider your opinions as the gold standard. I think you also know that I won't be shy about telling you when, on the rare occasion, I find your compass to be pointing somewhere other than magnetic north. This is one of those times."

The problem is Don that people here are not Don McRostie and others that you cited nor is Don or others providing their specific details AND what has resulted over time from them doing what they do.

My role here is different from your's Don. I'm in a position where I am contacted frequently by forum members who want us to repair things that went south with their builds. I have also hosted more than two dozen of you, OLFers in my shop for 2-3 day stays and I have personally seen what may result from learning to build a guitar largely from this forum.

In all honesty it's not always good either...... So much so that we won't work on small builder instruments unless we know the builder or they are established and experienced. To many cans of worms.....

With this said we are convinced that the more complicated those who advise folks here make things, the more we partially get into more advanced concepts without the direct hands on experience the more opportunity results to have someone's bridge that they glued at home come off in the middle of one of our classes. This did happen as well.

So we are concerned about concepts that stray from the foundational basics when the foundational basics we have observed were never..... learned.

If you want to put salt in your glue go for it man but don't be critical of others who promote being capable of using the tools that Luthiers use every day without adulterating anything first.....

You won't see me getting into the bowels of a discussion here about CF use or this finish or that finish. You will see me trying over and over and over and over again to instill some basic concepts that are the building blocks for all else in Lutherie. Learning to use and enjoy HHG AND learning to respect the requirements of HHG is very appropriate for a beginner builder forum. Extending open time with additives adds opportunity for someone to get it wrong and that's where I become cautious.

So we disagree and that's fine. I will continue to discourage any concept that offers a way to side step a basic Lutherie skill, HHG proper use because I am a living example of someone who had a traditional Lutherie education with a three year apprenticeship who did greatly benefit from repetition and having my subject matter intentionally limited to the basics until.... until I mastered them. Now I pay my bills and buy toys with this mastery of the basics and would hope that others if they wish would have this opportunity too.

With all of this said I would strongly encourage everyone here to learn to use HHG unadulterated for various applications including bridges and with excellent results before I would ever consider changing the chemistry of the glue to support a longer open time. HHG is one of the best tools we have but it will bite you if you disrespect it's requirements.

Nope not you Slim I have never seen one of your guitars.

Someone in this thread I believe asked why not use Titebond Bottled Hide glue if people are going to throw salt or pee in their glue (there is a thread on mandolin cafe about peeing in your glue pot...). We have found Titebond liquid Hide glue to be terrible stuff and there have been lots of failures reported from it's use. The only thing we think it might be good for is gluing frets but we prefer CA.

Your questions are excellent and understandable, keep em coming.

Yep it is all about learning but it's also important to fully understand step A before going to step C.

I would challenge everyone here to be capable of the following before you ever consider changing the chemistry of your HHG:

1). Properly prepare the bridge patch, bridge, glue and clamps for a bridge glue.

2). Execute gluing the bridge on properly with excellent cosmetics too and the bridge exactly where you needed it to be and no skating around on the glue.

3). Observe religiously a 15 second open time for the HHG before all clamps are in place and snugged down.

When you can do this well every time you will have learned things that will only serve you very well in understanding how HHG actually works.

So as some of you guys look for ways to extend the open time of HHG I instead offer why not learn to use it as is because it can be done and is done every day.

I use canning salt because it has no additives. If I remember later I will look up my recipe. I think I remember reading that to make it truly liquid it's something like 20% by weight. I only add a pinch.

A couple hundred years in the woodworking business of using urea in HHG is enough of a test of time to give me confidence in doing it. I have done my own tests too and the glue is always stronger than the wood.

About 25 years ago I built an instrument entirely out of Franklin LHG, a classical guitar, and I have not treated it very well and I still play it today. I would never recommend anyone use FLHG but none the less. It was probably a good fresh batch. I only used it becasue I didn't know better. I've never tried Old Brown but my understanding is that it's a better quality LHG.

Interesting article put out by a small (by their own admission) woodworking guild: https://emgw.org/ABOUT-US
Reading the article I found a lot of good information about hide glue. One thing I was not aware of is the use of vinegar to improve adhesion of hide glue. I have only used vinegar to - remove - dried hide and other organic glues (including Titebond) from joints before regluing. Being somewhat of a Sceptic, I would be inclined to find a more authoritative source before giving credence to vinegar as an adhesion promoter.
I do use HHG for many of the joints in the instrument building process, but will also use Titebond for joining surfaces that are not subject to creep and I desire the convenience of a longer open time, so have not resorted to pissing in the glue pot (which supposedly adds about the right amount of urea to the mix). Hide glue has many good properties, but so do other glues.

Taking a leak in the glue pot . Talk about using all your available resources .

I want to be very honest & clear I’m no luthier, honestly I’m closer to a destructive force of nature than a luthier. I’m a fiddler & tinkering fool of many things from metal fab, reloading, on again off again musician, among many many other things that tickles my curiosity. So I know I’m no pro but I do highly respect those of you on this forum who are & I appreciate your knowledge & opinions regardless if I agree or disagree because experience talking is worth listening to not just in luthiery but most things.

Know what you mean, clumsy is my middle name!

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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.