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Building up finish to 1/16"


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Hello,

     I need help building up finish on a guitar neck that I have sanded through too many times. The stain wasn't matching so I tried many different combinations and have created a big divot in the back of the guitar neck about 2" long by 1/2" tall. I have tried adding coat after coat of finish (water based poly and now oil based poly) but it barely seems to make a difference. does anyone have any other recommendations to build up 1/16" to level out this neck? I thought about gluing more wood down but don't want it to look unmatched and even have "edges" created by difference in wood being glued on. 

Should I try epoxy? It needs to be as hard as the maple neck.


Thanks. I can give a photo if needed.

 

Glen

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Hi and welcome!

4 hours ago, GlensGuitars said:

a big divot in the back of the guitar neck about 2" long by 1/2" tall

Huh? Considering that a neck is less than 1" thick my first thought was that you have sanded half of the thickness away! After giving it a second thought I then figured out that you may as well mean a spot covering an area of those measurents, the depth being "only" 1/16". After a quick check it changed to 1.6 mm which is quite a lot! That said, on a FarEast guitar they can put clearcoat on that thickly... A photo might help better understanding the situation.

Gluing more wood down to an irregular divot would require removing even more material for a level gluing surface - making a piece perfectly matching with the bottom of the divot is a mission impossible.

If the existing finish is very thick, one good option is to scrape it all off. After that you may find the divot being much shallower, maybe shallow enough to sand the entire neck that much thinner. If the divot is at either end you can even just try to blend it in by taking more off at the divoted end. After that you can then apply the finish you want, either similar to the original or something like TruOil or Crimson Guitar Finishing Oil (basically the same stuff). The "oils" add a protective layer but leave a "wooden" feel which actually makes a neck faster to play! Lacquer finish tends to grab on slightly sweaty palms which is also why some players sand the neck matte with some 1000 grit paper.

For just filling the divot epoxy/epoxy glue is an option but it will most likely not look similar to the rest of the neck. But it will most likely be solid and make the neck feel right.

 

 

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Thank you for the very thorough answer. Your'e right, the area is "2 by 1/2" and the depth is at 1/16". 

I learned the hard way that sanding sealer is like rubber. It does not harden when you put on 20-30 coats.  I actually am going to try epoxy, and maybe it will fill in the gap. Is it ok to apply a water based poly or oil based poly over lacquer?

A final thought was using turquoise powder or another colored powder. Since it's on the back of the neck it would rarely be seen, but would give the guitar a unique accent. Ever seen turned bowls with turquoise?

download.jpg

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Poly over epoxy should work just fine, just make sure that the epoxy has fully cured to prevent bubbling caused by evaporation. Sanding the epoxy matte up to some 1000 grit may help gripping.

Accenting the gap with coloured powder is a good idea as it will change the mistake to a feature. If you choose that path, may I suggest you do some more carving on the back of the neck. A coloured splotch is still a splotch but if you carve some vines and leaves that might end up a happy mistake. Something like these lines should be easy enough to carve free hand with a dremel tool and filled with the coloured stuff:

image.thumb.png.de091e14157e143dde036f26edacd887.png

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That's an interesting idea I had not thought of. I found when I was mixing and applying a lot of bubbles were in the epoxy. Do you know how to get rid of the bubbles  when mixing? It is a short setting (5 minutes) epoxy.

I think I'll just let it be epoxy this time. But you can see the oval area that is where I sanded down too far. I'll let you know how it turns out. 

20220717_135643.jpg

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11 hours ago, GlensGuitars said:

Do you know how to get rid of the bubbles  when mixing?

I've never used epoxy myself but I've seen it used and there's several ways to deal with bubbles. I suppose this video covers quite a many of the tricks:

 

From that angle the oval area doesn't look too deep, only of different colour most likely because it's bare wood instead of finished. Have you measured the actual depth? If you ask how, one method is to put a straightedge across the gap and then slide pieces of paper underneath. One sheet of regular paper like Post-It notes is about 0.1 mm or 4 thou. Coincidentally that seems to be a goal for an ideal finish as well! That said, especially the FarEast guitars may have a finish ten times that thick!

For what I've noticed filling a gap can be tricky. If the gap has straight edges like when a chip of lacquer pops off of a ding, the filling material tends to either creep up on the sides and leave the center too low, or it won't stick to the sides at all, just creating a ball in the middle. On gaps like yours where the edges blend into the surrounding you'll find out that the edges become higher as you apply the filler. It also may happen that when you start to worry about the raising edges the center still remains too low! So apply rather too thickly than not. It's easier to sand the excess off than to apply a second coat. Some thick tape (electrician's or similar) as a mold might help.

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Outstanding tips. I did lather on the epoxy so thick it left drips. I should have masked it off but it was so thick I thought it would not drip. The tricky part is after sanding down, I sanded the finish/stain off surrounding areas and I'm trying to match the stain color which never looks the same. It could be too late and it will have to do. If you had to fix small areas where stain and finish wore off, would you sand down the entire neck again and start over? It has crossed my mind but I don't want to make the neck any thinner. 

I finished this neck by hand wiping water based polyurethane from Stew Mac. I was afraid of fumes so I didn't want to spray or use lacquer. The result - if you're not careful, you can easily sand through and it's best to put like 20 coats. I'm not kidding, this stuff is so thin. I don't know if all water based lacquers are so thin. 

Learned many lessons from this neck. 

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13 hours ago, GlensGuitars said:

If you had to fix small areas where stain and finish wore off, would you sand down the entire neck again and start over? It has crossed my mind but I don't want to make the neck any thinner. 

Fixing small areas of stained wood is difficult. It can be done but it's dark art. You can start staining with a very weak solution of dye to sneak up to the desired hue but the dye may seep under the existing finish and make the original even darker at the edge of the damaged area. Thus sanding the entire neck down is often the easiest choice for a flawless finish. Remember that you should only be sanding the finish off, not much of the wood! But even if you sand the original dye off you'd only be taking a fraction of a millimetre away. That is, if you do it right... A scraper is a gentle tool and easy to control. When you get past the finish you can change to some relatively smooth sandpaper to get rid of any stain, starting maybe at 180 and going up to 400. Not higher to leave something for the new finish to grip. And of course moistening the wood to raise the grain between changing to smoother papers.

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