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I recently bought a guitar with a broken neck that I'm going to repair. (headstock snapped off --long break).

I've decided to use hide glue to do the repair.

Should I coat both surfaces with glue before clamping?

Or, will the glue on one surface provide sufficient coverage once the two pieces get clamped together?

NOTE: I will be pre-heating both pieces with a heat gun before applying the glue.

Thanks,

Dan

Hi Filippo,

Thanks! I'm glad to be here.

Actually, I've never used hide glue for wood-working before. I did a lot of reading, which may be why I sound so knowledgeable. I have done a lot of wood-working with other, modern glues such as Z-Poxy, Zap, etc.

The main reason why I selected hide glue is that, in my reading, I read about carpenter's glue and epoxy creeping. From personal experience, I know that epoxy will soften at around 160F-170F degrees, so that's why I'm not using Titebond, Z-Poxy, etc.

The decision came down to CA or hide, since neither creeps under heat. CA is a little easier to use because I can fit the joints together and clamp them, then wick thin CA into the joint, assuring a perfect fit. But, the permanence of CA is what is causing me to consider using hide glue instead. Even though this joint should never come apart, I'm considering what the next guy may think if he sees the joint repaired with CA instead of hide glue.

I've made a good double-boiler glue pot out of a Sunbeam Hot Pot Express that I bought from Target for $15. It keeps the glue right at 130F-140F. I also have a heat gun that I use for modeling that will concentrate the heat onto the parts and heat them to 150F+. And, I got Brooklyn Tool & Craft 192-gram hide glue.

I've made a few test joints and so far, I'm liking what I'm seeing from hide glue. The only thing I don't like is how thickly it seems to go on, which means quite a bit of squeeze-out while I'm clamping the parts together.

Thanks again for the advice.

Dan

Hi Filippo,

Thanks again for the advice on thinning hide glue. You're right. Right now, it's a little more like molasses instead of thick cream. Out of curiosity, how do you thin it? Do you mix in more water into the hot glue? This morning I added hot water to the hot glue and it did thin out. I was worried about getting it too thin and making a weaker joint.

I understand what you're saying about using epoxy resin. I use MGS epoxy for molding FG parts and I have no doubts that it would work well in this application, too. I've used it as glue many times. I guess I'm looking to use hide glue because that's what's traditionally used in instruments and I wanted to gain some experience using it.

FWIW, Z-Poxy is the trademark(s) for Pacer Technology's line of epoxy resins and comes in several different viscosities and drying times, including 5-minute, 30-minute and finishing resin. (See: http://www.supergluecorp.com/zap-brand-products/z-poxy-line)

Dan

There's nothing technically wrong with using hide glue for this repair, but it is advisable that you keep in mind it's sensitivity to moisture and humidity. Creep sets in at much higher stresses than will ever be seen from string tension. Consider that string tension averages around 160 lbs of force. PVA adhesive such as Titebond original form bonds on hard maple that exceed the wood, which fails on average between 3200 and 3400 psi. I have personally seen it cause wood failure at over 4000 PSI. At elevated temperatures (per ASTM D905, 150 F is tested) the adhesive will lose around half of its strength, literally the plastic softening, with full strength returning as it cools. From my experience in the adhesives industry, I have never seen or heard of adhesive failure due to creep on any part of a guitar. Temperatures well above 200 F would be necessary to create sufficient strength loss for failure to occur. The point I'm getting at is that there are good reasons why the guitar industry has relied on PVA over hide glue since the early to mid 1960s, and never looked back. Unless there is a good reason, such as historical authenticity, hide glue is more finicky and generally not worth the trouble.

Like hide glue, PVA can be thinned with water in order to ease application. A 5% addition of water will cut viscosity in half with no affect on performance, similarly a 10% addition of water will create a 75% decrease.

Hot Hide or Fish glue are my choices but HHG is my 1st choice.

_________________
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

I would think that the general best practice is to coat both surfaces. But I have never used hot hide glue. It just seems to me that a broken neck which typically is the type of fracture that has a lot of peaks and valleys in it that would be best coated with glue on both surfaces rather then depending on the one coated surface to coat the other surface during clamp up. A glue like Gorilla glue will fill in areas as it expand and so as per their instructions you only glue up one surface and wet the other.

FWIW I've done at least a hundred of repairs like this with full strength Titebond, Diluted Titebond, LMI glue and CA and I can honestly say, I've never ever had a head stock repair come back again. Though I have seen reworked repairs come through my shop. No matter what glue you choose to use the mating of the pieces must be flush, clean, and as perfect as you can possibly get.

Coat both surfaces. It can't possibly do any harm unless you allow it to gel before clamping or you get the glue way too thick. From my experience the strongest HHG joints are the ones where the surfaces have already been sized with HHG. Probably not necessary on the vast majority of joints but anything with end grain and it becomes much more important.

On headstock breaks , the one thing Todd mentioned is the clamping method. I have a few cawls for Martin , Gibson and most electrics. The key is to get the head stock flat. You need to be good at puzzles . I have used Epoxy for a shattered head stock as this is better at gap filling but if you can get clean mating use the wood glues.
The worst head stock I had was on a Gibson Gospel. It was sent to me from Hawaii. The broke off under the nut and there was pieces missing. The owner also tried a reglue which made for a difficult fix. I used epoxy on this. I also had to make a rig to hold the headstock at the angle. Once the epoxy set I had to address the area of missing wood.
I flipped the neck in my mill and used a dovetail bit to cut out an area so I could replace the shatters wood and glued area. I made a filler of fresh wood and used glue here as I had clean surface area and good wood to wood contact. Once the glue set I ran 2 splines from the neck barrel to the headstock . Also wood glue. While this may seem drastic you had to see the neck , the wood in the area of fracture was just splinters. Once all the glue cured I reshaped the neck in area of repair from about 1st fret to behind the nut. The neck was painted black and the finish work all but hide the final repair.
Sometimes your best tools are your creativity and imagination . The guitar sounded phenomenal and I see why the customer was willing to pay the price of the repair and shipping back to Hawaii from PA. I should have taken pictures

_________________
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

Thanks, all, for the thoughtful replies.

In the end, I decided to use HHG, especially since I spent the time and money making such a neato glue pot.

Unfortunately, I did not coat both sides as some suggested. In retrospect, I probably should have coated both sides, but I had a decent squeeze out when I joined the parts, so I don't think this will be an issue. The glued parts sound and feel solid when tapped. I'm getting a uniform 'ringing' noise when I tap on the back of the neck with no dead or dull spots, so that tells me that I've got a good coat of glue on the joint.

First, the break, and it's an ugly one. I don't think a couple thin coats of lacquer will hide this one.


And, a few shots of my neato homemade glue pot. It works pretty good. It keeps the glue between 130F-140F. Wife had a conniption fit when she saw I drilled two holes in this brand-new 'kitchen' appliance. Had another one when she saw I was using a coffee cup to melt the glue.




And the repaired neck. First, the good side.


The ugly side. Lots of thick, catalyzed finish missing here. I'll probably use some sort of tinted, thickened epoxy to fill the gaping crevasses. The underlying wood is mostly there and level with each other, which is good.


The top side. The cracks in the veneer are mostly filled and level. Some light sanding/polishing should make this mostly invisible.

145 degree F is where you want to be.

Looks like it came together pretty well. You can hide it if you do a black burst around the joint

I'm curious to know how you clamped it? Because a joint like that has the tendency to slide under pressure. For those of you who use HHG is there enough tack in the glue to where you do not need to pin that joint some how? When they brake clean off like that I always pin the joint for that very reason.

Yep. It's glued. There was some squeeze out, which I wiped up while it was still soft and wet. If you look really close you can see a little of the glue line along the 'ugly' side. I intentionally kept the part of the joint by the nut a little dry to minimize the squeeze out in this area so I could keep the area where the nut mounts as clear of glue as possible.

Thanks for the suggestion. That was the route I planned to take. It's hard to see in the pics, but the joint is pretty level. As you suggest, the next step is to get the finish filled in and level with the surrounding area.

I'm probably not going to try to hide the repair on the back of the neck. As long as it's strong and smooth and reasonably close to the color of the existing finish, then that's what really matters to me. My daughter has already expressed an interest in the guitar, so after I fix it and play it for a while (to make sure the repair is a good one, dontcha know?) then I'll give it to her.

Thanks again for all the advice. If there's interest, I'll keep posting pics of the repair as I go.

Dan

I'm embarrassed to say how I clamped it.

It worked, but I don't think I'll use that method again.

I was going to make myself a couple of custom cauls for the top and bottom of the neck. I was worried about not getting the glue clamped in time, so I looked around for some spring-type clamps I could use, and settled on using a few CAPOs.

The rubber grips did help keep the neck joint from slipping as I squeezed it together.

Like I say, this time it worked out okay, but in the future I think I'll use more traditional methods.

Dan

How long should I let the glue 'cure' before I start repairing the finish?

Might be an idea to string it up and give it a few days, just to make sure that the joint is a good one. That's the type of break where I like to size the pieces first.

Answering your question of how long to wait to start finish repairs. If you have no big rush, wait a couple of days to let moisture from the glue escape before you seal it up.

I was thinking about doing this and for the very reason you suggest. I can see the value in doing that. It would really help guarantee complete glue coverage.

I used a hobby heat gun, which can get the surfaces pretty hot if I'm not careful. I also used an infrared thermometer to check the temp of the surfaces and they were about 150F-160F degrees.

That's a good suggestion and one of the reasons I chose HHG over CA. I wanted to have the option of dissolving the glue joint and starting over, should the need arise.

I got lucky this time. The neck alignment seems to be pretty perfect and the joint seems to be solid. Of course, the proof will be when I string it up. I need a new nut, otherwise it would already be strung.

Nope. Other than wanting to play it, I'm in no big hurry and would rather wait and let the moisture out.

I'll probably follow Michael N.'s suggestion and get it strung to make sure it plays okay before I work on the final finish, just in case I need to fix the joint.

Thanks.

True, but heating it to 145 will allow the glue to retain more heat which will delay the point it starts to gel by a little bit.

Hi Todd,

My homemade glue pot doesn't keep a constant temperature.

It's got a thermostat that clicks on when the temp drops to a certain point, then clicks off when the high temp point is reached.

In my case, it's adjusted so the temp clicks on when the glue temp drops to 130F and off when it reaches ~140F.

I did notice that the amount of water in the boiler seems to affect how high the glue temp will 'float' after shut off. With more water in the boiler, the glue temp will continue to drift up to 145F-150F after it shuts off at ~140F.

With less water the temp remains more constant because the water heats up quicker. Of course, it cools down quicker, too, which means that the boiler turns on and off more often.

So, my question (this time) is whether the glue temperature fluctuating (cycling) between 130F and 140F-150F is undesirable, or whether this is a non-issue?

Dan

I thought you said 125 to 130 was good. Well, sounds like we agree.

Do you all think it's okay that the temperature of the glue cycles between 130F and 145F as the glue pot heats and cools?

I doubt it will be any problem. Most forms of electric Glue pots will exhibit temperature fluctuations. My own does and I've been using that particular one for over 10 years.