Wood, Hide, or CA for Crack Repair

[Doug Cannon]

I have five short cracks on a 40 year-old mahogany back Gibson that were a result of lack of moisture. I've rehydrated the guitar, the cracks are now well aligned, and I'd like to know what type of glue would give me the best results and whether cleating is necessary for the inside in this case.

Although I've always leaned towards Titebond for most wood repairs, I see quite a few people using Thin CA glues for tight cracks and wondered if this might be an appropriate repair for it. As I've said the cracks have closed and are clean, it's a nitro finish (Gibson), the surface is even, and I know that the CA has "wicking" or capillary tendencies.

Crack #1 (Pictures below) is under the center seam bracing....that won't need a cleat. #2 and #3 are about 2 inches long and near the kerfing and I'm wondering if cleats are necessary. There is no movement on either side of the cracks when pushing on them (There was when I first got the guitar. Thankfully there are no cracks  on the mahogany sides or spruce top.....small miracle. There are also no cracks in any of the back bracing or kerfing.

I appreciate any and all suggestions,

Thanks so much!

Doug

[Hesh Breakstone]

Thanks Lee!  Hope you are well.

[Roger Häggström]

Hot hide glue is thin, so there should not be a problem. The best way is to put glue over the crack and then move the top on either side. The capillary force will suck in the glue. You can feel on the inside when the glue has penetrated the crack properly. Then wipe away the excess glue with a damp cloth. I think the glue is watery enough.

[Doug Cannon]

I greatly appreciate it.....I wasn't excited about using anything "permanent" on wood....CA feels like a quick fix to a much more complex (and long term) problem.

Thanks!

[Russell Vance]

Hi Doug,

CA has it's place and for a set of given parameters and situations it's "the best". ie; the most suitable glue for what is in front of us. Obviously, CA is not "the best" if you wish to preserve the Nitrocellulose finish adjacent to the cracks.   So what is the best for one repair may not be so for the next.

Which is what Hesh so clearly put with his entreaty to consider more than just opinion or common practice when assessing a repair strategy.   Common practice does not necessarily mean best practice which is where the more experienced guys and product science come into play.   New glue systems are mainly developed because they are better or more specific in their application.  However, everything new isn't necessarily better, but a lot of old stuff isn't either.

So, I have attached some definitive general stuff from a reputable Mag for yr consideration - It's a repost from a fellow forum member who I thank,

Regards,

Rusty

    

[Doug Cannon]

Thanks Rusty.....

Great article! Very interesting that HHG was so effective on mahogany and other open pored woods. Conveniently it's also thin enough to get into tight cracks. Would have been great if they had also included CA in their testing, but I'm not sure that "Fine Wordworking" really wanted to go there. Also not surprised by the efficacy of PVA as I know Gibson has been using it successfully for quite some time now and it can be heated or steamed apart.

Thanks for the reply,

Doug

 

[charley erck]

Good article on glue. Very methodical, except the area of high strength where only the wood broke, but that's in another realm. Whenever I'm planning to put my guitar in a hydraulic press, I know which glue to choose !

[Lee Gendvilas]

Hello Rusty, thank-you also for your expertise and comments. As with Hesh's posts, I learn a lot from you also. Great article on glue-thanks for posting.

Lee

[Roger Häggström]

The best article I have ever read on the topic of hot hide glue (and other glues) is made by Per Hallgren. Per is a highly respected Swedish maker of classic guitars. It's in Swedish unfortunately, but there is Google translate :-)

http://www.hallgrenguitars.com/Per_Hallgren,_Gitarrbyggare/Artiklar...

[Hesh Breakstone]

Hey Rusty thanks for that.  Hope to see you this summer when you are visiting!

Do you know that the Northwood Seminar is on for this summer?  There is a thread on the OLF forum with details.  

[Russell Vance]

HI Hesh, Paul, I'm in country 24th August through 8 Sep in Baltimore (Home of Ratzilla) and will PM in a month or two when the sched gets done to arrange a day up your way for Pro/social pursuits.   Just missed the timeframe  for the Northwood Seminar, wow, what a line up of talent there!   2018 could be good.

C'ya

[Walter W Wright]

i've seen this before (had to like subscribe and then quickly unsubscribe from the website to do so).

eye-opening stuff, but i have to wonder both about the "creep" factor with moderate warmth of the various glues, and how the test would have gone had they actually clamped the wood together (y'know, like folks usually do).

i also wish that CA and fish glue had been part of the tests, and that they'd compared regular titebond original to the titebond III rather than the frankly off-brand elmer's stuff.

[Howard Klepper]

Back in the last millennium, in an era called the 1970s, a self-taught luthier who had 40 years of woodworking experience named Arthur Overholzer wrote a book about guitar making.  Among the things he said was that if your bridge was well fitted to the top, and you used the right glue, you actually did not need to clamp because the glue would pull the joint tight as it dried.

The glue was called Titebond.

I don't know for sure where the current myth about the unique magical property of hide glue to clamp itself by pulling joints tight got started (possibly on a well-known guitar repairer's website?), but it is just that--a myth.  Any glue that sets by evaporation of a solvent will shrink when it dries, and both hide and aliphatics are often capable of making an adequate "rub joint" that is allowed to set without clamps.  But neither will make anything like an optimally strong joint that way.  If anything, the advantage goes to the aliphatic, because first, it has more cohesive strength so if the joint is not tight it is stronger than hide; and second, it does not pass through a gel state where its elasticity will tend to hold the joint surfaces apart (recall that hide glues are rated by this resilience in their gel state).  Back before aliphatics were in wide use, books on gluing wood used to advise retightening the clamps on a hide glued joint after about an hour, because the joint that was tight when the glue was liquid would become less so after it had gelled.  This was the standard practice in many furniture shops.

Now, in the next millennium, we have people actually saying that a joint glued with HHG can be unclamped as soon as the glue has gelled, because of the magical property, unique to hide glue, of clamping itself.  Hogwash!  If the joint is not under a lot of stress, it may work, but it is far from optimal.  And Titebond will also shrink and close the joint--some--as it dries, and make as good a rub joint as hide.

As for Paul's question, below, the answer is because you want to create a permanent bond, and your strategy is to get it right the first time.

Hide glue has certain advantages such as wicking well when thin, and being reversable in joints that are intended not to be permanent.  It does not have the magical properties currently being ascribed to it many places on the net.