gluing crack in soundboard

[Tom Derrick]

Hello,

    I need some advice about fixing a crack in my 1960's Goya G-10. Having successfully glued the extension of this crack from the bridge to near the rosette--I don't remember what adhesive I used there --, I am now overcoming several  failed attempts to fix the same crack from the lower end to the bridge (see photo).

    My second unsuccessful strategy was to delicately scrape the opened seam with a Beaver knife/ scalpel, and apply hot hide glue. I  worked the seam up and down to distribute the glue and applied light downward clamping pressure with a Klemsia clamp. No adhesion after it dried.

    So, what glues have people used to make this kind repair? How about a viscous "Superglue" like Stew-Mac thick?  Or should I mix up a bigger and more viscous  batch of hide glue (LMI ground hide glue)?

    As for  clamping, I am considering getting a pair of those disk magnets and pulling the crack into alignment that way.  My heavy duty 2 x 4 clamps would span the lower bout, however, I'm loathe to balance that beam above the instrument or risk crushing the sides. 

     I will appreciate the thoughts of experienced luthiers about making this  repair.

[Ned Knepp]

Well, I'm not an experienced luthier but I'll give my two cents anyway.

You didn't say how the cracks formed but unless it's from an impact, it probably formed from shrinkage of the wood. You also didn't mention whether or not you attempted to rehydrate the guitar before attempting a repair it or how long it's been cracked. 

Judging from the picture and record of attempted repairs, I'm guessing that the crack either needs to be clamped shut across the lower bout Or filled with a spline. If it were mine, I would consider filling the crack with a spline at this point but that could easily change if I could actually see the guitar. The glue that exist in the picture makes it hard to tell what the crack actually looks like.  IF the guitar isn't too dried out and the crack is gaping even just a bit, a spline will knit the top while relieving the tension that caused the crack in the first place BUT I would only do that after I was sure the guitar was properly hydrated.  

BTW,  hot hide glue should hold it just fine IF it fits together but it's not a good idea to try to use glue as a filler in a case like this. The crack should be tight for the glue to work properly, what ever glue you decide to use.

[Tom Derrick]

Thank you, Ned.

   If I install a spline, what tool would be best to cut a V-shaped channel?  I'm thinking a carving chisel might have about the right contour.  Stuart-Macdonald's "Power knife" (item #5359) is too expensive an option, especially when you add the Foredom tool.

    Repair people must do this kind of repair routinely. What are the usual hand-tool  techniques?

   It's 102 degrees in Terre Haute, and my Goya hangs in a seldom air-conditioned space, so, yes, the instrument is probably extremely dry. Putting a hydrator inside might reduce the crack but I doubt it will close it.

What is a reasonable method of restoring moisture inside?

Playability is not an issue but the "gaping" crack is an aesthetic concern, even on this inexpensive guitar, which I've played for as many years as Theodore Bikel or Burl Ives.

[Tim Mace]

I think based on the number of attempts maybe that crack wants to be there .You could put a patch inside to hopefully stop it from spreading and forget about it if it doesn't interfere w/playability plus it's not by most standards an exspensive "unit".How important is it? Maybe just cosmetic?Knowin' me I'd have given up after trial 2!Looks like a weather crack that took the grain w/it........and they usually play well from that ancient time period when Theo Bikel played a Goya!!!

 

[William F.Eden]

Check out some of the old threads. It is all explained in them how to fix your crack...Bill............

[Paul Verticchio]

Tom,

Ditto to what Bill said.  This has been discussed to death & beyond in the archives. We're not a bunch of snobs nor are we lazy.  To go over the process yet again would be superfluous when there is so much identical information available through a little self motivated research..

Also Frank Fords FRETS.COM has several excellent pictorials.

Any way you look at it, you're going to have to undo what you already did and take all mating surfaces back to bare wood for proper glue adhesion.

In all cases, the very first thing you MUST do is get the guitar to a normalized hydration level.  If the guitar isn't properly humidified, any work you do will be undone WHEN it is finally properly humidified. Tops can buckle too.

Given the age of the instrument, it's maker & the condition of the top, I wouldn't hold out for a great looking repair.  If the instrument is in otherwise, good playing condition, my gut reaction is: fill it with epoxy & level it out. Actually, looking at the grain pattern on the top, that crack was destine to develop.  It may actually be simply a bad piece of top wood.

It will not affect the (any) $$ value the instrument may hold. These were cheap utility/campfire instruments at best. TheG-10 was their bottom of the line (entry level) nylon string guitar. In excellent condition, these currently sell for between $35 & $50  (on a good day).

Best of luck (-:

[Ned Knepp]

Tom, when I want to humidify a guitar, I use a ziplock baggy with a fews holes in the UP side and a fairly damp kitchen sponge. If I have a case available, I'll lay case and the guitar down in an out of the way place with the sponge laying inside the sound hole, making sure the holes on the bag are up, close up the case and leave it for a few weeks. I only open the case to check on the sponge and to gauge the progress. In your case, check the crack to see if it's closing. It can take weeks to rehydrate a guitar if it's very dry. 

If the guitar doesn't have a case, I will usually do pretty much the same but I will plug the sound hole to keep the moisture inside. Balloons work very well for this. There are also a slew of devices on the market to hydrate your instrument, most or all of which use the sponge inside of the guitar routine in one way or another. Most are usually easier to use then my approach but they cost money. I actually have a couple of different models but the both seem to require a lot more attention then my sponge in a bag approach.

If you can't close the crack enough that way to just glue it, you can use a SMALL "V" tool to clean up the crack and get some slope. I have done this but I felt that the resulting slot was unnecessarily wide at the top. I have some small triangular wood files that do a good job and keep the slopped sides at a steeper angle so the spline isn't so wide at the top.  I can  pull it through the crack rather than push it which, to me, is the less risky way to approach it. The files are actually a set of micro or jewelers files. I've got a lot of different sets of these from course rasps to very fine (useless on wood) curved files. The set that works best for this are labeled as "Swiss Pattern Files" and have several different shapes that are suitable for this purpose. My favorite is shaped like a knife blade but with a fine pattern of teeth on the "blade". 

I uses a very sharp knife and scrapers to shape the splines.