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Hello All,

I've always been a fan of hot hide glue since that was the only glue worth using when I started building, back in antediluvian times. I do recall some people reporting bad experiences with either urea modified hhg---to keep it liquid at room temperature---or with fish glue, due to their being hygroscopic---I'm really stretching my memory here...can anyone refresh it?

Cheers,

Brian

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ooh yeah, curious too, especially about fish glue.

i assume it's an old tech, but it seems to have been "rediscovered" in recent years, i certainly never heard of it before stewmac started selling it.

i've been using it for a few years now for jobs where i wanted those hot hide glue properties (drawing itself in for "rubbed joints", finish-safe and reversible) but needed more open time and wasn't as worried about high strength. that's mostly meant things like top cracks and loose braces on acoustics.

Here is an info sheet I came across that addresses your question.

https://emgw.org/resources/Documents/Meeting%20Presentations/2016%2...

Hello Mark and Walter,

The only time I'm concerned about open time is when gluing on the back. To extend that a minute or so, I heat the back and the body up warm to the touch with two drugstore heating pads. That gives me a total of 2-3 minutes to get the back in place, and a bunch of heavy rubber bands strapping the back joint closed.

I get a chance to examine the joint when I rout the back binding rabbet. Only once have I had to add a bit of hot glue to a short open space.

Stew Mac's description of their fish glue includes the word "flexible", so it sounds like there is some sort of additive. I think that I'll "stick" with the hot stuff. 

Attached is a .pdf of my HHG stuff---it's way cheap!

Cheers,

Brian

I think the problem with fish glue being hygroscopic is an Internet rumor from one users bad experience. Repeated again and again. It may have been a bad batch of glue or old glue (fish glue have a shelf life, dry granulate of HHG have no such thing).

I use it to glue back the bottom on old guitars, it takes half an hour or so to match the bottom to the sides. I use HHG for the neck and bottom block just in case, the first parts of the bottom to be clamped in place. You can also use fish glue to glue non woods to wood. Pearl inlays or metal for example. Fish glue is a better filler and stickier than HHG. When dry it is not as crystal hard a HHG (but still hard), a good thing for bindings or pearl inlays. But other than that fish glue have pretty much the same properties as HHG including the way it contracts when drying. It's dangerous to leave blobs of fish glue on top of varnished wood, the sticky properties of the glue will most likely cut loose a bit of varnish when drying and contracting!

Hello Roger,

After ruminating about it overnight, I think that it was the HHG that was modified to keep it liquid at room temperature that was causing the problem. If I remember rightly it was urea that was added.

Cheers,

Brian

Well, it really is fish glue that is said to be hydroscopic. There is a lot of bad rep about liquid hide glue too. I blame most of it on the limited shelf life of both fish glue and liquid hide glue. Keep an eye on the production date and keep the bottle in the refridgerator :-)

Hello again Roger,

I'll keep it simple, and only use HHG. 

By the way, storing shellac flakes in the fridge really works. I recently had occasion to dissolve some flakes that had been in the fridge for more than three years, and they all dissolved!

Cheers,\

Brian

Hello Mark and Walter,

The only time I'm concerned about open time is when gluing on the back. To extend that a minute or so, I heat the back and the body up warm to the touch with two drugstore heating pads. That gives me a total of 2-3 minutes to get the back in place, and a bunch of heavy rubber bands strapping the back joint closed.

I get a chance to examine the joint when I rout the back binding rabbet. Only once have I had to add a bit of hot glue to a short open space.

Stew Mac's description of their fish glue includes the word "flexible", so it sounds like there is some sort of additive. I think that I'll "stick" with the hot stuff. 

Attached is a .pdf of my HHG stuff---it's way cheap!

Cheers,

Brian

Hello again All,

I'm sorry for the multiple posts. I keep trying to include a .pdf of my HHG setup, and I keep getting an error message---I've contacted Frank....

I can send the .pdf to anyone that wants it. Just email me with a request to:

Brian@BrianBurnsGuitars.com

Cheers,

Brian

Fish glue I believe is/was used for accordion bellows. I have never had any reason to experiment with it and have learned to control HHG to get consistent, repeatable results with it. Early on I did experiment with adding Urea to HHG but found I really didn't need it after refining heating and assembly methods. Urea can be added up to about 10% to increase open time. It is sold at farm supply stores and is quite inexpensive but you really don't need it.

I use Infra Red lamps to heat the work, multiple lamps when needed. Clamp light fixtures are cheap and versatile means of directing the bulbs. Infra Red will not readily heat things that are reflective and plain White paper does a decent job of masking where you don't want heat. I have been using Fluorescent corkscrew bulbs with an A bulb base socket, zip cord and plug to work inside of instruments with a large enough sound hole to use them. They generate enough heat to warm the interior adequately and used with Infra Red on the outside for applications like bridges. On occasion, I have also used forced air hot guns to heat something up.You can keep the lights on through the entire clamp up, which also helps with the open time.

You can go past just warm and heat things until they start to feel hot. Obviously, you don't want to damage any finishes. Hide glue gels right around 90 degrees and you want the parts be be a good margin hotter. When you heat hide glue, 145 is about the upper margin where you want to heat it. Beyond that, the glue will start to degrade faster. Multiple heatings of a batch will also start degrading the glue. Make new batches for high strength joints but you can re-use batches for several sessions for things like cleats. When I am done with a batch, I put the bowl I use in a ziplock baggie and put it in the freezer. It will keep this way until you start to see freezer burn.

I don't do new builds but when I need to put a back on an instrument after repairs, I don't clamp it up all at once. I first run through a dry clamp up, which helps me figure out where to start and in which order to place the clamps. Generally though, I will start at a neck or tail block and and also an area of side to the right and left of the block(s). I work my way around wedging the back open a slight bit and applying the glue with a thin palette knife and clamping as I go. That said, I don't see why you couldn't do a new back all at once with hot lamps and a go bar rig. Just do a dry run through first, a step that many don't do. The rehearsal will save time when you apply the glue! Tidiness counts, have everything lined up in order and easy to grab, fumbling around costs time.

It is also helpful to first prime the joint with an application of hide glue. Wood is absorptive and one of the big reasons open time can be so short with HHG. Brush the joint, both parts just prior to glue up, then do it again when your ready to set and clamp. Doing this also increases open time. It's OK if the initial application goes mostly dry on you, the new hot stuff will re-activate it.

Viscosity is another way to help tame HHG. Generally speaking, viscosity should be about like pancake syrup for most things. I go a bit thicker for high strength joints like bridges and neck joints and use watery thin for crack repair and violin plates. I use a Herdim hide glue heater and had my potter daughter make extra bowls for it. The bowls can be stacked on the heater; one with normal consistency glue and the other with watery thin. I can prime joints with the thin stuff and follow up with the more viscus in this manner. Thinner glue (more water) also gets you more open time.

Be careful about getting the glue on clamp faces. The glue can bond to finishes and cause an unhappy result when the clamps come off. Otherwise, don't worry to much about drips and glue mess. Warm water and a soft cloth will clean things up after the glue has dried. I keep wet paper towels at the ready to get the worst of it when it drips but wait until later to do a proper clean up.

I have a few images that shop the clamp lights and a guitar back attached in three sessions (I only show 2). Hope this helps.

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