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| Help with a crack http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=14957 |
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| Author: | kevinc [ Fri Dec 14, 2007 7:39 am ] |
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I recently glued the top on my first build and now I just noticed the beginnings of a small crack/separtation in the upper bout area bass side on the top. I'm not sure if it was caused by a humidity issue or possibly one of the clamps shifted a bit when I was gluing up the top and caused some undue stress. Either way I'm looking for some help with what to do now to keep it from opening up more and causing some real trouble. I have not sanded the top to the final thickness yet. I was wondering if the repair will show if I wick in some thin CA and then sand it all down. Would this be the best route? It doesn't seem to go all the way through the top. If I put my finger inside the body and press below the crack it doesn't move, but this is also a pretty stiff area of the top. Any help would be great. Thanks, Kevin Here is a link to a picture of the crack and also one of the body next to a couple of it's big brothers. http://i116.photobucket.com/albums/o24/kcaccavaro1/guitarbod y020.jpg http://i116.photobucket.com/albums/o24/kcaccavaro1/guitarbod y025.jpg |
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| Author: | Barry Daniels [ Fri Dec 14, 2007 7:55 am ] |
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Hot hide glue makes for the least visible repair on spruce. After gluing the crack, I would put a small cross grain, spruce cleat on the inside. |
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| Author: | Kent Chasson [ Fri Dec 14, 2007 7:56 am ] |
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More info would be helpful. Do you know what the RH is now and what it was when you braced? Did the RH ever drop more than 15% below that of when you baraced it? If the top was arched, is it still arched? If the crack is open on the top and closed on the bottom (braced) side, that sounds like humidity but I would expect to see some other pretty obvious signs of low humidty too, like an arched top gone flat or convex. If it is humidity related and it was braced between 45 - 50%, you should be able to get the RH back up there and the crack will pretty much close itself. Then work some HHG into it. CA can soak in to the open grain and stain. |
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| Author: | JohnAbercrombie [ Fri Dec 14, 2007 9:36 am ] |
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Kevin- You've gotten some good advice from Kent and Barry. This could even have been a pre-existing crack in your top that's just become obvious now. You might want to blow the sawdust out of the crack as a first step- it'll let the crack close up better if it 'wants to' with humidity change, and it will also make your repair less visible. BTW, if you're not set up for 'ordinary' hide glue, you can use Knox gelatin from the grocery store and standard hide glue prep steps. Do some trials before doing your guitar repair. Cheers John |
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| Author: | kevinc [ Fri Dec 14, 2007 9:51 am ] |
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I've really tried to keep the humidity under control since I began working on the top. The top is still domed and there are no other signs of low humidity. It was braced at 45RH and it really hasn't varied more than about 5-6 degrees ever since. It's possible that the crack developed before I started working on the top since my workshop is in my bedroom and I live in a 200 yr old wind tunnel of a house. I admit I wasn't as vigilant as I should be about the humidity before I started working on the guitar. I was thinking of a dark sunburst for this guitar so the CA staining the top may not be an issue if it is covered by the burst. If HHG is the best choice I will go with that but I've never used it before. I'd have to order some before I could try which could delay things for a week or two. I'm moving from NH to South Carolina at the end of the month and I expect there will be some changes in temp and humidity from here to there! Is there anything else I can do to limit the effects of humidity change on the unfinished body?Would it hurt to put a thin coat of laquer or sanding sealer on the raw wood to seal things up for the move? |
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| Author: | JohnAbercrombie [ Fri Dec 14, 2007 10:00 am ] |
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Kevin- CA can do some nasty staining on spruce (green/yellow); I'd avoid it on your top. If you don't like the Knox option, white glue or titebond are options, but not as good as hide glue. Hide glue is pretty simple to use- you just need a small jar and a saucepan for heating water for a job like this. I wouldn't mess with putting finish on the body until you are ready for it; it won't prevent movement due to humidity changes. If your guitar is in a 40-50% RH environment, just seal it in a plastic bag and pack it up with the rest of your stuff. Cheers John |
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| Author: | kevinc [ Fri Dec 14, 2007 10:02 am ] |
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First, thanks to all for the help. This is exactly why I lurk on this form on a daily basis. There is so much I need to learn. John, I was typing (slowly) and didn't see your response before I posted. I like the Knox gelatin idea. And based on my experiences so far, I will definetly practice on something else first. |
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| Author: | Alexandru Marian [ Fri Dec 14, 2007 1:14 pm ] |
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What about fish glue? It is easier than saying "fish" . Did any of you used for spruce crack repair before? I did not, but I am just looking at some glue squeeze from under the bridge I just clamped and it is pretty much transparent, if not a bit creamy. In any case the same color aged spruce is..or shellac... |
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| Author: | JohnAbercrombie [ Sat Dec 15, 2007 5:13 am ] |
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Alex- I use fish glue and like it a lot. As you say, it seems to dry very clear and hard. Great for bracing, bridges, and I've used it for bindings as well. Very sticky stuff. For a crack repair, I think I still prefer hot hide glue, since it 'gels' up quickly and cleanup of the excess is a bit easier than with fish glue. It's also quicker. But, any of the alternatives (not CA or epoxy) would work here, I think. Cheers John |
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