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| Author: | Wes McMillian [ Fri Jan 23, 2009 9:39 pm ] |
| Post subject: | Burned finish repair (pics) |
So any of you repair gurus (gurii?) have a fix for this? While removing the bridge on a 70's Alvarez dread, the finish got burned at the leading edge of the bridge. Made me even madder once I got the bridge off and saw the copious amounts of glue used from factory  right over the finish, too. Probably could've knocked it off cold with less damage - no wonder the bridge was lifting.Here's what I'm working with:  
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| Author: | Cal Maier [ Fri Jan 23, 2009 10:27 pm ] |
| Post subject: | Re: Burned finish repair (pics) |
Bummer Wes, I feel for you. It looks like the finish may be some kind of poly urethane, as it looks pretty thick for nitro. If poly you could use CA glue to drop fill and touch up after blisters are removed. If nitro I would try drop filling with nitro. Either way you may still see the heat discoloration around the blister, unfortunately. What did you use to heat the bridge? I usually use some asbestos sheeting around the bridge before applying heat, it protects the finish and directs most of the heat to the bridge area only. Cal |
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| Author: | Joe Sabin [ Fri Jan 23, 2009 10:35 pm ] |
| Post subject: | Re: Burned finish repair (pics) |
This might be VERY wrong for an instrument, but petroleum jelly will pull the burn out of a finish. If others think it's an ok idea, then you put the petroleum jelly on the burn (lots of it to soak up the burn from the finish), let it sit for several hours. Carefully wipe it off then clean the residue with mineral spirits. If not all cleaned up, use another dose. I've taken cigarette burns out of a finish with this technique. Fortunately you didn't lose any wood, that's the hardest to replace. |
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| Author: | David Collins [ Fri Jan 23, 2009 11:25 pm ] |
| Post subject: | Re: Burned finish repair (pics) |
I hate to say it, but you're pretty much screwed on this one. There is no good fix that is easily or quickly done. You'll obviously have to clean up, scrape, etc., the bubble area, but the ambered and browned finish around it is permanently discolored. You can try to sand that area out and touch it up, but you can tell by the difference in color between the finish under the bridge and outside of it, that clear lacquer will not give you a perfect match. Try to tint the lacquer to match, and aside from that alone being a challenge, trying to feather it in along the area you sand out can be near impossible to pull off cleanly. There's just all sorts of things that can add complications to a seemingly simple touchup here, leading to bigger and bigger area of more and more obvious repair as you go on. There are a few tricks that can help, but none really easy to do. Removing the pickguard and stripping a straight path of finish (scraped, not sanded) from the bridge to the pickguard may seem counterintuitive, but can leave you only to mate new finish with old along grain lines and not across them. Even then you will often need to size the wood before finishing, and matching the color can be a challenge - worth trying on a more worthy instrument, but not on this. Are you doing this for a customer, a friend, or for yourself? If it is for a customer, first thing you have to do is call them before making any decision. Explain the situation, apologize, and propose some solutions, certainly including not charging for the work. Invisible repair is a long shot, and would take a whole lot of work to even attempt. A quick clearing of debris, glue sizing, superglue touchup, sand and buff could be done fairly quickly. If they don't care how it looks, then they get their guitar back with a splotch and an apology, but the bridge reglue is free. If it's dead mint otherwise and they do care about how it looks, then you'll have some other things to figure out. Try the touchup and risk making it worse? Offer a list of other work you can include free of charge to compensate. There's no quick fix or easy way out of this one. I've never heard of the petroleum jelly trick. I can't quite picture the chemistry of what would be happening there, but it could be worth a try I suppose. Just don't get it on the bare wood, as the area that has bubbled is certainly lost for good. |
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| Author: | Wes McMillian [ Fri Jan 23, 2009 11:55 pm ] |
| Post subject: | Re: Burned finish repair (pics) |
Cal, I used a halogen lamp for most of the heating with a heat gun for backup. I think the heat gun is what did the damage. I did have the area masked with cardboard covered in aluminum foil, just looks like I had an escape path when I decided to use the heat gun. David, thanks for chiming in with your experience here. I kinda had in mind removing the damaged area completely and drop filling as best I can but, as you said, the old nitro has yellowed with age and would make for a hard match. I have no experience color matching old, yellowed nitro for repairs, any recipes to share? Would be a good thing to learn, for sure. I've always heard exactly what you're saying about finish repairs - that a small job can quickly turn into a bigger and bigger mess the more you mess with it and you're often best stopping with minimal work and intrusion into the old finish. I did make the new BRW bridge just slightly oversized. Not so much as to make it obvious, but enough to help in the cover-up. The damage still shows, but not as bad. I think I can make the repair reasonably well by, as you say, removing the bubbled area and trying to match the old finish. If anything, I figured I would go slightly darker to blend with the discolored area, which I'm likely stuck with. I figure a little too dark would look better than too light here. BTW, even with the slightly oversized footprint, the new bridge weighs 27 grams opposed to the 42 grams the old bridge had with the hardware. This repair is actually for a friend. I know he wouldn't say anything, but it would always haunt me. I have a hard time leaving something in this kind of shape. |
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| Author: | Michael Dale Payne [ Sat Jan 24, 2009 12:29 am ] |
| Post subject: | Re: Burned finish repair (pics) |
Both the lamp and the gun were the culprit. Neither were the best of heat sources for this task. I suspect the gun caused the blistering and the lamp cause most of the discoloring. A bridge iron or bridge heating blanket would have been better choices. You have to get a 3/8" thick piece of rosewood to 110-140f with out getting the surrounding finish higher than 80-90f so you want the heat to be focused and radiate over a controlled area. If you stop and think about what happened I bet see and understand why and what happened. |
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| Author: | David Collins [ Sat Jan 24, 2009 12:45 am ] |
| Post subject: | Re: Burned finish repair (pics) |
For a quick minor touchup, I would remove the bubbled area and cleanup the edges. Then I would size the area with some diluted hide glue - this can prevent some unwanted darkening of the spruce that fresh lacquer can bring. Then for matching the amber of an old finish, I've yet to find an artificial amber pigment that really does a great job. Some can do okay, but hard to get perfect. Then best tinting tool I've found yet is still good old shellac. Amber, blonde, orange - many will work, and it's very flexible in mixing and is very controllable simply by how it's applied (and can be rubbed off as well if you go too dark). Then let it cure for several days to weeks depending on how thick you lay it. Then lacquer over the top. With a bit of practice, you can even get pretty good at feathering in edges, though making it invisible is still quite a challenge. Side notes - it's probably an acrylic lacquer or something similar. The ambering that we so often associate with nitro is by no means limited to it. It's always been a "problem" of pretty much all clear finishes, though in the last few decades formulas have become much more resistant. Still, nitro will work just fine for a touchup, especially if the area is sealed with shellac. These finishes were certainly a synthetic though. I'm also not a big fan of making bridges oversized to cover damage like this. Even if the area is severely damaged, I typically view an oversized bridge as detracting more from the instrument than the finish damage left visible. As much as it may bother you to have to look at the damage if it happened on your watch, it's part of the history of the instrument at this point, and hiding it is usually pretty evident as being just that. Bring it more than .040"-.050" larger, and then it just starts to look like a double-whammy of damage plus a cover-up attempt. If it were a more historic or valuable instrument I would strongly advise against the oversized bridge. In this particular case I'm not bothered enough by the oversize idea to strongly advise against it - it's probably fine for this guitar. I personally would probably keep the original footprint though. Edit: As to heating technique, I would blame the heat gun and possibly the masking. In spite of all the silicone heaters, heat cartridges, and other heating systems I use for other purposes, the 250w heat lamp is still my favorite tool for heating bridges. I feel I have much better control over where and how much heat I am applying than with the other options. I do mask in to about 1/16" - 1/8" over the bridge itself though, and not just up to the edge. |
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| Author: | jordan aceto [ Sat Jan 24, 2009 10:19 am ] |
| Post subject: | Re: Burned finish repair (pics) |
David collins is painting a very accurate picture of what you are in for here. This happened in a shop where i was working a while ago, on a newish nitro finished guitar, and the customer was MAD. The solution in that case was to professionally refinish the entire top, which included pulling the neck. There may be a handful of people out there with magic touchup skills, for most of us poking at an area like this just makes it bigger and worse, and with a picky customer ANY evidence is not ok. Davids hide glue sizing/shellac/lacquer approach sounds right for this job. |
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| Author: | Ken Franklin [ Sat Jan 24, 2009 10:40 am ] |
| Post subject: | Re: Burned finish repair (pics) |
Here's a tip from Frank Ford for making amber lacquer to match older instruments. http://www.frets.com/FRETSPages/Luthier/Quickies/AmberLac/amberlac.html |
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| Author: | Wes McMillian [ Sat Jan 24, 2009 12:16 pm ] |
| Post subject: | Re: Burned finish repair (pics) |
Thanks for the link, Ken. I knew I had seen something on Frank Ford's site and had hunted all over for it. Sadly, I don't have a year to let my nitro age, but that's a good reminder to set some out. I'm going to continue on with the repair and see how it winds up. The bridge I made is just very slightly long on the front side and only covers up a little bit of the area. I don't think it looks bad, but we'll see once the repair is done. About a minute on the belt sander and I can have it back to original dimensions. And, yes, I had determined (too late) much of the problem could have been alleviated with a smaller mask that overlaps the bridge a little bit. As long as the middle of the bridge gets hot, the thinner wings would most definitely transfer enough heat to soften up. Along the lines of what Michael was talking about. I will definitely never use the heat gun again. Gotta learn to be more patient. Oh, well, live and learn. Thanks for the feedback, guys! I find the repair side of luthierie extremely interesting and love the unique solutions the world class repair guys come up with to tackle unusual jobs. Guys like David Collins, Frank Ford, and Dan Erlewine - who so freely share their years and decades of trial-and-error experience - are life savers for those of us still learning the craft. |
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| Author: | Tai Fu [ Sat Jan 24, 2009 11:18 pm ] |
| Post subject: | Re: Burned finish repair (pics) |
Have you thought of using an oversized bridge to cover up the damage? |
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