Repair And Restoration
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Need advice on my first repair job
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Need advice on my first repair job
I would really appreciate some advice on this repair that I need to do. I’ve built a number of (classical) guitars so far, but this is my first repair job. I have already set the expectations with the customer that I can probably fix it structurally but the repair will be visible. The guitar is modestly priced and of no historical significance so it seems like an ideal project to take on as a first one. The guitar suffered a blow on the lower bout. I’ve been able to pull out what i could and assessed the following :
– I have inspected the bracing and there are no signs of damage. The side has a slight crack which appears to be only the poly finish. There are no signs of the crack from the inside. Purfling and lining seems to be salvageable.
– The top split from the side for a length of about 21 cm, the majority of the split is between the purfling and lining.
– A part of the top got completely crushed (now cleaned out in the picture attached). One Peone got completely detached
– Red line is where the top has detached from the Peones
– Green line is where the peones are still attached to the top but got detached from the sides.Judging by the overspill of glued parts, the guitar was originally assembled using regular white glue.
Unless I break the top further, which I would like to avoid, I am not able to clean the areas from existing glue. I am aware that most glues don’t bond to areas where white glue was previously used. I am also aware that i’m not necessarily going to be able to put much pressure where the peones got detached from the sides, although I should be able to apply some pressure on the area where they got detached from the top.I am wondering what’s the best glue strategy :
Hide Glue – Will give me a better joint with less pressure applied – particularly due to the ‘pulling’ effect hide glue has when it cures. I have to work fast though and I’m not sure whether i’m able to work it well into the joint enough before it gels up. If I go down this route, i will use an infrared lamp to keep things warm as I work. (This is what I normally do on my builds)
Titebond – Will give me decent open time, but i’m not sure it’s the best approach, particularly if I still have gaps and since there is old white glue present (although I’m not sure whether hide glue is actually better in this respect)
A good cyanoacrylate such as gluboost thin – I haven’t used thin so far, only ultra thin which will probably go straight through and bond nothing. I wonder if this is a viable option.
I think I should rule out epoxy but if anybody knows better, please do tell
Plan is to first deal with the part where the Peones detached from the side (green line), then reattach the top (red line), then once everything is structurally ok, deal with the insert.
Lastly, the finish is poly. Any recommendations on the best way to get this done? I only do French polish and I’m not kitted out for spraying. I’m thinking of using shellac as a sealer then Gluboost fill’n’finish. At that point i’ll decide on whether i’m able to buff it out as is or if it requires a lacquer flash coat. (I saw various posts on the gluboost flash coat but it doesn’t seem to have made it into Europe yet 🙁
The missing peone will get glued in from the inside at the end.
I also have no idea how much to charge for such a repair!
Any feedback or suggestions would be most welcome!
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13 Replies
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This one might be good to talk about on a zoom call. Would you be willing to do that and we can record it and attach it to this post as well ?
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That would be amazing, Ian! Let me know what we need to do to organize that
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email me at ian.davlin@gmail.com
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Thanks so much for this, Ian.
As discussed, the epoxy I could source relatively easily is the StewMac from Madinter.
StewMac Stewart-MacDonald Epoxy, Slow setting, clear
I checked our local Amazon, but it seems to be pretty much an extension of what you would typically find at a hardware store.
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Here is a long overdue update on the repair! It took long as I was loothing in my mentor’s workshop back in Spain for a few weeks. I also wanted to get some feedback from the owner a few weeks after handing over the repaired guitar.
The epoxy worked wonders. In the end, I worked with a combination of West System G-Flex and 105/206. I used G-Flex wherever I could, but the 105/206 worked better in some tight spots as it flowed better through the cracks. With the use of 105 I avoided the need to remove a section of the binding/purfling.
With a camera on the inside, I kept injecting epoxy until I could see it oozing out from the bottom of the kerfing blocks which were still attached. The inside got a bit messy but I guess this is unavoidable.
Once that cured, I added some further epoxy from the inside with a syringe to further stabilize the joints, and also to glue the blocks which had gotten completely detached.
The new piece of cedar was glued using titebond. Here is where I in hindsight I should have paid more attention on matching the cedar. All seemed pretty close before I put the piece in, but once it, it really stuck out like a sore thumb.
After some research, I opted for a set of shellac touch up colors from Kremer in Germany. This was not the best choice and in retrospect I should have gone with dyes (Stewmac Colortone or Oldwood dyes which are more readily available in Europe). The Kremer shellac pigments would have been great for localized touchups (cracks etc.. But not to cover a relatively large area)
The structural part was straightforward and all went well. What I grossly underestimated (even after the many references to this in Ian’s video) was the cosmetic part. It was a headache to match anything. I tried to apply it using an airbrush – ok for color but it was completely the wrong texture. Finally I went across the grain with some sandpaper and created some artificial medullary rays. Initially I was trying to build up color, but in the end, it seemed like it worked better backwards where I over applied the color then sanded it down until I more or less matched the rest. I think the finish still leaves much to be desired, but I did warn the customer multiple times that it is NOT going to be unnoticeable.
Next came Gluboost over the new cedar plus some of the old. Gluboost worked really well and I was very happy with the way it blended into the poly finish.
Smoothing was done with 3M Gold up to 800 grit, then with micromesh up to 12,000. Final buffing was done using Menzerna 2500/3500 (I love this polishing compound. Comes from Germany and I consider one of the best of the ones readily available in Europe) and an orbital polisher.
In the end, the client was happy with it. Emphasizing the cosmetic shortcomings from the start, I think, helped a lot in setting the right expectations.
I charged for 4 hours of work (in reality it took me way more but I think 4 hours was a good reflection on how long it should have taken if I had prior experience and did everything right from the start)
Takeaways :
– Prior to talking to Ian, I would not have considered using Epoxy. It was a great learning where, when and how to use Epoxy.
– Great experience with West System Epoxy. I did a lot of tests prior to getting it on the guitar, and none of the other brands I tried so far match the adhesion properties of West System.
– Most of the work was on the cosmetic side. I need to pay way more attention to this in the future and plan it out better from the start.
– Matching the run-out was something I did not give enough attention to. In hindsight, it’s obvious : mismatches are further worsened, not improved, once the finish goes on. I really should have been much more careful with matching the unfinished cedar right from the start.
Thanks again Ian and the Looth Group for your invaluable help!
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Rather than replacing the missing/damaged peones, I would consider gluing in a basswood or spanish cedar fitted block covering the entire area of damage (plus a little more extending out past where the new top material will be joined to the existing), much like is done when making an arm rest. I worry about the sonic integrity of the critical top to side junction using small replacement peones. I would consider removing all that are suspect, shape the block, then fit it and glue it.
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Looks fun!
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So, finishing is my weakness and have been testing away on junk guitars. The terminology is fascinating. Can someone (Ian?) give me the spelling and meaning of (going to use my phonetics from the pronunciation here) “shecoiance”? Cool vid! Thanks!
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Here you go 🙂 Chatoyancy – Wikipedia
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Thank You Claude! The terminology is fascinating! How is the repair coming?
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I’m planning to start it on Friday. Unfortunately the Stewmac epoxy i ordered came from a bad batch and didn’t cure properly on testing, so I had to abandon that one. I did however manage to find West epoxy in Europe from a boating supply store in Hamburg. Explore epoxy resins & hardeners now | TOPLICHT. It should be arriving tomorrow!
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It makes me realize how spoiled we are here in America. I shouldn’t complain as to the time it takes to get stuff and that I can get it at all.
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