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I wasn't careful about the humidity in my shop and the guitar I'm building just developed a crack in the top.  It's unfinished except for several coats of shellac on the top.  Anything I can do to rescue it?  Can I force glue in?  Is so, Titebond or hide?  Is it best to do it while still dry and spread?  Any suggestions will be appreciated.

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After another day in 45 percent humidity the crack is gone.  I wonder if there's any sense in trying to force glue into it now (or where it used to be) of just leave ot properly humidified until I finish it with nitro.  It appeared to be a surface crack that didn't go all the way through.

Jack,

you need to glue it, Wood never forgets and Nitro will "find" this crack and take up the hairline appearance if the crack is not stabilized and secured. Titebond Original has less creep than Titebond 2 of 3 so it is the preferred glue for luthiery in the Titebond series.

Don't get caught wishing away problems - this one is serious and in a noticeable position and requires a fix.

Regards, Rusty.

Thanks Rusty.  It's been suggested that I use Hot hide glue rather than Titebond.  What do you think?

Jack,

There are HHG specialists reading this who can help you.  We don't use HHG and can only comment on other glues as our experience dictates. 

I use Titebond in this application as it has a useful working time and the capilliary action and ability to ease it/massage it into the finer cracks to a good depth and then subsequently clamp it and manipulate it is an attractive set of reasons to use it. 

R.

I've been assuming that you know but since it hasn't come up I though I'd remind you that you will need to place some cross grain patches along the crack on the inside to help it hold up. Welcome to the exciting world of "through the sound hole repair". 

I use an infrared lamp to keep the top warm as I work. The hide glue is mixed watery thin, that will help it's capillary abilities. I  liberally apply the hide glue along the entire length of the crack, pile it on. The extra volume of hide glue helps it stay hot longer. Work the crack from inside, gently pushing upward, letting it open slightly. I pretty direct about this but you have time as long as the infrared light stays on. Wipe the excess off of the top with a damp rag and repeat 2 or 3 times, you want it to really soak in. It's helpful to have mirrors inside, you can see when the hide glue makes it way through the crack and it will help keep any glue drips from creating extra work on the interior. Wipe off excess glue again with a damp cloth but don't worry about getting all of it. You can do some final clean up with a hot, damp rag after it's dried. You will also need to do some light sanding afterwards as well.

White paper or tin foil will protect the instrument where you don't want heat. I applied the glue with the pipette in the glue pot.

You can see here how I have applied the glue. You can also wiggle the top halves gently from the outside where needed to get the glue in to the crack. The edges of the crack will swell slightly but they will return to normal after it's clamped and dry.

Inside shot with mirror. See the glue soaking through?

Obviously, I have enough time to stop and take a picture but you want to keep things moving along.

A well aligned crack lick yours should behave with a plexiglass caul with very light clamping pressure. Here I have just clamped using the back, did I say light pressure?. Magnets can do this job too if you need some pressure inside the instrument.

Leave it alone over night. A few hours is probably enough but why rush.

Hide glue has a few advantages over Titebond; Invisible to almost invisible repair with a clean joint. When hide glue dries, it actually pulls the joint tighter. Ease of clean up, hot water. It is resistant to heat and will not "glue creep". A crack repaired this way that returns can be re-done with hide without fully cleaning the joint of glue, it will re-activate. A Titebond crack that reappears would likely need to be splinted.

Cleats would be extra insurance but not absolutely necessary unless the crack returns.

Hope this helps. It doesn't seem like a big deal to me but I have been playing with hide glue for some time. The safety net though is hide glues ability to re-activate glue in the joint, if things don't go according to plan.

Good luck!

Great help Paul.  Thanks so much.

Your welcome Jack, hope this helps. Please let us know how you fair.

Paul

Thank you all for your help. I decided to go with the HHG.  After much scraping and sanding, it's pretty much invisible.

That's great, Jack.

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