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PostPosted: Mon Feb 11, 2019 9:10 am 
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Mahogany
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This is only about the second time that I've attempted this, but I'm having some pretty bad issues.

So, I have a little hole in the top of this polyurethane-finished guitar. This should be easy - Drop in some poly, let it dry, repeat a couple of times, scrape it down with a burred razor blade, then strip sand and polish. Unfortunately it's been nowhere near that easy for me. Right now I've got a lot of sunken-looking areas around the repair, and it's uglier than the hole was originally. How do I save this tar baby before it gets any bigger?

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PostPosted: Mon Feb 11, 2019 10:12 am 
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I have never heard of someone drop filling polyurethane. It does not burn in to itself, and that is probably the root of your problem. CA would do a MUCH BETTER job.



These users thanked the author Barry Daniels for the post (total 2): fumblefinger (Fri Apr 19, 2019 10:54 pm) • Chowlie (Mon Feb 11, 2019 10:14 am)
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PostPosted: Mon Feb 11, 2019 10:14 am 
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Mahogany
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Barry Daniels wrote:
I have never heard of someone drop filling polyurethane. It does not burn in to itself, and that is probably the root of your problem. CA would do a MUCH BETTER job.
I actually did try superglue at first, but then I had a little issue when I was trying to take it off. The razorblade didn't exactly shave it down, but pulled all the glue off in one chunk taking the underlying polyurethane with it. So it basically just made the damaged area much bigger for me to repair. That's when I started layering it with polyurethane instead.

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PostPosted: Mon Feb 11, 2019 10:54 am 
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Mahogany
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I did a little more strip sanding and polishing to get it slightly better. I'm a bit more satisfied but not completely yet. It's still not polishing up the way it should.

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PostPosted: Mon Feb 11, 2019 11:04 am 
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Koa
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I don't think you will ever get poly to work for this. The photo shows that the drop fill does not "wet-out". It just sits in the hole kind of pulling away from the sides. Basically, this is an issue of surface tension.

When using superglue, you might need to scratch the bottom of the depression with an exacto knife so the glue has something to hold onto. When scraping with a razor blade just take small shavings and there will be less chance of pulling the drop-fill out.



These users thanked the author Barry Daniels for the post: Chowlie (Mon Feb 11, 2019 1:16 pm)
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PostPosted: Mon Feb 11, 2019 4:31 pm 
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Tough to tell but it looks in the photo like you may have sanded through the clear coat to the sealer below around the repair. That means it will not buff out so you have likely graduated to Finish Repair 102; how fix the repair you sanded through. Witness marks will be an issue on almost any but airbrushed spot repairs. Padding on several coats of medium CA with a Paper towels would be the next step here.

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These users thanked the author B. Howard for the post: Dave Rickard (Mon Feb 11, 2019 7:10 pm)
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PostPosted: Tue Feb 12, 2019 1:11 am 
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I learned the hard way that when you fill with CA you have to let it completely set up. I usually do small amounts at a time and give it at least 24 hours between fills. Then I'll let it sit for a couple of days after just to be sure before I try to scrape.

The other culprit here may have been the burred blade. I don't burnish mine, just tape off the sides so it doesn't gouge at the outside. The burred edge may have lifted the fill.


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PostPosted: Tue Feb 12, 2019 3:34 am 
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No burr on the edge of the blade. Tape the ends of the blade and scrape very lightly.

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PostPosted: Tue Feb 12, 2019 9:03 am 
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After reading everyone's comments yesterday I went ahead and layered some super glue on with a paper towel. I'm gonna let it set up until at least tomorrow night before I start back on it.

So scraping it down with a razor is still the preferred method for leveling it out? I think one problem I had before with the super glue was the fact that my blades were so thin. I bought them from the paint section at Lowe's, and the edge is so dinky you can really see it moving when you hit anything substantial. I might break one of my boxcutter blades in half and use that instead.

Does this look normal?

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PostPosted: Tue Feb 12, 2019 10:17 am 
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Are you using activator? what brand/type CA?

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PostPosted: Tue Feb 12, 2019 10:21 am 
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B. Howard wrote:
Are you using activator? what brand/type CA?
No activator. Store brand CA from Lowe's.

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PostPosted: Tue Feb 12, 2019 5:48 pm 
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I do not like the way that looks...are you wiping it on or dabbing?

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PostPosted: Wed Feb 13, 2019 8:28 am 
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B. Howard wrote:
I do not like the way that looks...are you wiping it on or dabbing?


I did a couple of wipes first, then started dabbing to apply more at once.

I scraped it down last night and it's looking pretty good. I put a tiny drop right on top of the dent again because it looks like there still may be a tiny void there.

How should I proceed from here? I'm thinking about using acetone on a Q-tip to remove some of the outlying CA so I won't have to sand out as far.

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PostPosted: Wed Feb 13, 2019 11:55 am 
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That looks much better! You are using a medium CA correct? Wiping is the best way, 3 wipes about 5-10 minutes apart in three different directions and then a wipe with activator, wait 5-10 and repeat if needed.

No acetone and something bigger than a 1/2" across should not be scraped with a razor but rather sanded. I wrap sandpaper around a rubber eraser to sand these type repairs.

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These users thanked the author B. Howard for the post: Chowlie (Wed Feb 13, 2019 11:58 am)
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PostPosted: Wed Feb 13, 2019 12:02 pm 
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B. Howard wrote:
That looks much better! You are using a medium CA correct? Wiping is the best way, 3 wipes about 5-10 minutes apart in three different directions and then a wipe with activator, wait 5-10 and repeat if needed.

No acetone and something bigger than a 1/2" across should not be scraped with a razor but rather sanded. I wrap sandpaper around a rubber eraser to sand these type repairs.


This is very thin CA I'm using - mainly just because it's all I had on hand. I have some Gorilla CA gel, but that's obviously not right for this application. Do you have a particular brand/type of medium CA you'd recommend I purchase to have on hand?

Rubber eraser is a good idea - it will conform nicely to the guitar's top. My only worry is with accidentally sanding too deep and taking off the clear coat in an even bigger area than before. The only sticky-backed sandpaper I have is 320 and 600 grit, but I could glue a small piece of 1000+ to an eraser. Would you wet sand that or no?


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PostPosted: Wed Feb 13, 2019 12:37 pm 
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I don’t use poly for this kind of repair.

I use either resin, or acrylic. The acrylic makes really easy repairs. It buffs out super glossy. But it’s not as hard as poly. Works great on chips, but not as good on areas where wear happens.


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PostPosted: Wed Feb 13, 2019 12:42 pm 
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Oh. Here’s some acrylic repairs:

ImageImage

ImageImage


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PostPosted: Wed Feb 13, 2019 12:55 pm 
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Wow, those look really good!



These users thanked the author Chowlie for the post: Photoweborama (Wed Feb 13, 2019 1:34 pm)
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PostPosted: Wed Feb 13, 2019 1:24 pm 
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I'm not sure I understand the wiping technique with a paper towel. To you drop CA on the repair and then try and wipe it level? Do you dip the paper towel in CA and try to pad it on like French Polish?

I've always just dropped in CA in sessions till it's jsut above level then use the taped razor blade technique followed by wet sanding and polishing. But I'm curious to better understand the paper towel technique.


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PostPosted: Wed Feb 13, 2019 3:46 pm 
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I use Bob Smith CA. Have tried others and they are not all the same. I keep coming back to old Bob Smith....

I'm not sure I understand the wiping technique with a paper towel. To you drop CA on the repair and then try and wipe it level? Do you dip the paper towel in CA and try to pad it on like French Polish?

Fold a small piece of paper towel up into a square pad about 6 layers thick and and inch or so square. Drop a bit of medium CA onto the pad and wipe it on. Once and done or you'll glue the pad to the surface.

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These users thanked the author B. Howard for the post: jfmckenna (Thu Feb 14, 2019 11:34 am)
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PostPosted: Wed Feb 13, 2019 3:47 pm 
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Photoweborama wrote:
I don’t use poly for this kind of repair.

I use either resin, or acrylic. The acrylic makes really easy repairs. It buffs out super glossy. But it’s not as hard as poly. Works great on chips, but not as good on areas where wear happens.


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What brand & type acrylic? I typically do any Gibson repairs in nitro as that is the original and customer preferred material.

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PostPosted: Wed Feb 13, 2019 3:57 pm 
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B. Howard wrote:
Photoweborama wrote:
I don’t use poly for this kind of repair.

I use either resin, or acrylic. The acrylic makes really easy repairs. It buffs out super glossy. But it’s not as hard as poly. Works great on chips, but not as good on areas where wear happens.


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What brand & type acrylic? I typically do any Gibson repairs in nitro as that is the original and customer preferred material.

I just use Rust Olium from Walmart. I use it on Gibson’s also. I can’t afford the time if the nitro does not cure quickly. I can’t wait 15 years for the tacky ness to go away! [FACE WITH TEARS OF JOY]

I just tape it off, spray layers and dry between coats with a fan. When it’s higher than the chip, I sand level and buff. I use Mguires ultimate polishing compound. Comes out looking like glass.

Oh, here’s another acrylic repair I did on a 1961 Gibson Les Paul / SG Standard...ImageImage


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PostPosted: Wed Feb 13, 2019 4:59 pm 
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"Rust Olium"? Holy Cow that does look good!

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PostPosted: Thu Feb 14, 2019 11:22 am 
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Is this the product?

https://www.amazon.com/Rust-Oleum-Automotive-253366-11-Ounce-Acrylic/dp/B006ZLQKQG/ref=sr_1_5?keywords=rustoleum+acrylic&qid=1550161050&s=gateway&sr=8-5


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PostPosted: Thu Feb 14, 2019 11:44 am 
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Rustoleum paint? Hmmm, well it's hard to argue with those results. Typically if I use a paint to match color I will clear coat it with Nitro, that way it can be buffed and polished. For small spots I just wait a week and polish out.


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