Scratch Repair with GluBoost - Luthier Tips du Jour Mailbag
In this episode, luthier Robbie O’Brien shows how to fix a scratch in a guitar top using Glu Boost products.
Video Transcription
[on-screen text reads: Luthier Tips du Jour Mailbag]
Mailbag question: I left a fingernail scratch in the top of my guitar when french polishing, how can I fix it?
Robert O'Brien: Today's Tips du Jour Mailbag question comes to us from Utah. "Robert, I was almost done with the final spiriting off session of French polishing my guitar when I left a small scratch with my fingernail in the top. After a few choice words, I asked myself, "What would Robert do?" So what would you do to fix this? Jason in Utah."
Jason, this happens a lot more often than I like to admit. In fact, it happened to me recently on a nice commissioned seven string classical with a cedar top that I'm building. I was almost done with the finish when I left a small scratch up in the cutaway section. So I've got to fix it. The first thing to do is keep calm. There is a way to fix it. Let me show you how.
How to fix scratches in your guitar top
So Jason, there's a couple of very small scratches right here, they go into the wood. Cedar is pretty soft. It's probably not even showing up on the video here, but believe me, I know they're there. And when you put the finish on it, everybody knows they're there. So I've got to fix them.
Apply thin viscosity GluBoost
The way I'm going to fix this problem is by using the GluBoost products that I got from LMI. I'm going to use the thin viscosity, the ultra-thin viscosity, it's like water. CA glue. And I'm then going to use the GluBoost accelerator. So I'm going to start just by putting a small amount into the top of a yogurt cup, and then I'm going to take one of my wife's sewing needles here and use the very tip of it just to grab just a little dab there and put it right into that spot, in the low area. It's very tough to see even under the light here, so you want to use just a very small amount on the tip of that needle, and it's going to take several applications, but it will settle in there and level that low area.
Apply GluBoost accelerator
So now that I have the low areas there where my fingernail grabbed and left marks, I'm going to go ahead and accelerate it. Now, depending on how long it takes you to apply the CA glue, you may not need to accelerate it at all. If you're in a hurry, hit it with a little bit of the GluBoost accelerator, and it should be fine.
Now, one of the good things about the GluBoost accelerator is it doesn't leave white bubbles in the CA glue. A lot of CA glues out there will do that, but the GluBoost accelerator will not do that.
Scrap and level
The next thing I do is take a razor blade that I've wrapped some cellophane tape around and I left an open part into the middle. That way I can come across the top of it and scrape this right down level with my surface.
Sanding
Next, I'm going to hit it with a hard sanding block and some 320 grit paper. There we go. Everything's leveled. Now I can go right back to finishing and those marks will disappear under that CA glue.
By the way, this is also a great little tip for those fingernail marks you get from playing. Put a little dab in each one of those, level it the way I showed you, and then refinish over the top of it and those will disappear.
So Jason in Utah, I hope you found this information useful. Now, there are a couple of things you can do to help avoid this issue in the first place. One is to cut the fingernails off the French polish hand. If you're right-handed, cut them off. If you're left-handed, cut them off. However, if you're a player and you use fingernails, that creates a problem, so it's not always feasible to cut them off the right hand. In that case, use a glove. That will help keep this mistake from happening. Hopefully it won't happen to you again, and happy finishing.
[on-screen text reads: More Luthier Tips and online courses available at www.obrienguitars.com. Private and small group guitar building and finishing instruction available.]
