Acoustic guitar Finishing advice

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Jonathan Cressman
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Acoustic guitar Finishing advice

Post by Jonathan Cressman »

Hello everyone!

I am new to guitar building, am just nearing the end of my first build (a steel string acoustic), and am trying to decide how to finish it.
I've done a fair bit of research, but have found many things quite confusing, and so am hoping for some guidance. I should preface that I am looking for a finish that doesn't require spraying equipment, as I don't have it.

So, after much research, I have come up with two options, Brite tone top coat by crystal lac, and Royal-lac super blonde. Just wondering if anybody has any feedback about if either of these is more forgiving to work with (I have very little experience finishing), or any general advice about the products?

And I also have a couple specific questions. Both of these products have a complimentary sealer product that the respective companies make (CrystaLac sanding sealer to accompany the Brite Tone, and Seal lac to accompany the royal lac). My understanding is that I need to get the sealer for whichever product I choose, and apply a couple coats of it to properly prepare my guitar for the top coat products. However, I have also heard a lot about pore fillers, and am somewhat confused, as some people make it sound like a sealer product (like either of the two I mentioned) will act as a pore filler as well, but some people make it seem like you need to have a separate pore filler, making it a three step process, with a pore filler, sealer, and top coat. just wondering if anyone can clear this confusion up for me? Do I need a separate pore filler, or is just the sealer good enough? My guitar has a cedar top, and cherry back and sides, so not very porous woods.

Thanks, any advice is greatly appreciated!!

- Jonathan

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Barry Daniels
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Re: Acoustic guitar Finishing advice

Post by Barry Daniels »

You do not need pore filler because cedar and cherry are "closed pore" species.

I am not familiar with either of your two finish selections so I can't help you there. But I would recommend that you consider Tru-Oil which is a wipe-on varnish like product that is VERY user friendly. There are tons of discussions on the forum about Tru-Oil which you can search for and read up on.
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Barry Daniels
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Re: Acoustic guitar Finishing advice

Post by Barry Daniels »

What kind of wood did you use for the neck?
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Jonathan Cressman
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Re: Acoustic guitar Finishing advice

Post by Jonathan Cressman »

Hi Barry, thanks for the help!

Tru-oil hadn't been on my radar, I just looked it up, and it seems promising. One question about it - Someone I know had, a while back, given me the advice that whatever finish I decide on, I should stay away from any oil, because he said it it kind of "clogs" wood, making it less resonant, and negatively effecting sound quality. I guess that perhaps this person was wrong about that, as it sounds like Tru-Oil is pretty accepted as an acoustic guitar finish?

And my neck is made out of mahogany, with a rosewood fretboard

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Barry Daniels
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Re: Acoustic guitar Finishing advice

Post by Barry Daniels »

Actually, your friend is correct about the negative effects of an "oil" finish. But Tru-Oil is a polymerized linseed oil, which means it cures and will actually build a film on top of the wood if you apply enough coats.

Also, your mahogany neck is open pored and will need a pore filler. Aqua Coat is an easy one.
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Alan Carruth
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Re: Acoustic guitar Finishing advice

Post by Alan Carruth »

Oils don't really 'clog' the wood, but they do have high damping, which tends to 'eat' the high frequencies. Straight 'boiled' linseed oil never really stops hardening, and shrinks as it does, which can cause problems, Nor does it form a water proof film. The low molecular weight components of most drying oils can penetrate very deeply into wood, which adds mass as well as damping. I don't know about Tru-OIl; the polymerization process should mean that it's all large molecules that stay near the surface.

Natural resins are often used as finishes. Typically they are low in damping, and form a good film on the surface, but they can be brittle and chippy. They are applied by dissolving them in a solvent, such as alcohol, and painting or padding them on. They tend to be chemically stable, but remain soluble in whatever solvent. The most familiar one is shellac, which is a resin that has been modified through ingestion by the lac bug. It is tougher than many resins, and cross links over time to become insoluble. There are a lot of others, though. Shellac is not as hard as many of the 'modern' finishes; about 1/3 less hard than nitrocellulose lacquer. It also is soluble in alkaline water solutions, and some people have sweat that seems to eat it right up. Used as 'French polish' it is the traditional finish for classical guitars. The materials for FP are all edible (within reason), and it's said to be the only finish that can be applied in a sand storm. It takes a bit of skill to do, though. Shellac, and most resins, are easy to touch up as the new coats 'burn into' the existing surface.

Some of us use brushed oil-resin varnishes. Oil and resin are cooked together to form a co-polymer, which has some of the advantages of both. The oil confers a measure of toughness and flexibility to the film, as well as making it resistant to most solvents. The resin stabilizes the oil chemically and confers hardness. Because of the oil content varnishes can be among the most beautiful of finishes, with a 'depth' that is hard to match with anything else. 'Varnish' is actually a name for a class of things, like 'wood', and there is as much difference between a good short oil floor varnish and a long oil spar varnish as there is between ebony and pine. Because varnishes harden by a chemical reaction involving the drying oil used in making them woods that have non-drying oils can interfere with hardening. This varies, of course, with some varnishes being largely unaffected by woods that can be problematic with others.

A friend of mine says that whenever there are a lot of ways of doing something it's a sign that either everything works, or nothing does. There is no 'perfect' finish. All you can do is choose one that has features you need or want, and drawbacks you can live with.

Jonathan Cressman
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Re: Acoustic guitar Finishing advice

Post by Jonathan Cressman »

Thanks guys, both of those posts help clear things up a lot!

I've been looking around, and Tru-Oil looks like a really good option, I think that's what I'll go for! I've looked around at how people apply it, and just have a couple questions I was still confused about.

Firstly, to what grit should I sand the raw wood in preparation for the Tru-Oil?

And secondly, my understanding is that Tru-Oil is quite forgiving about how you apply it, that you just wipe it on with a cloth in fairly thin layers. However, I was getting mixed messages about whether or not to wipe it off or not. I saw stuff that said to just wipe it on and leave it to dry, but other stuff about wiping it on, waiting for a couple minutes, and then wiping it off. This is confusing to me, as wiping off or not seems like a fairly large difference, but maybe it isn't? Any advice on which one to do?

And then my other questions is around the different coats. My impression is that you can apply a coat every couple hours, up to about 4 coats a day, and that you are supposed to scuff the surface with something between each coat. My question is just what should I use for this? Sandpaper, and if so, what grit? Or something else?

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Barry Daniels
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Re: Acoustic guitar Finishing advice

Post by Barry Daniels »

Sanding to 220 grit should be sufficient for wood to be finished. I like to apply Tru-Oil in very thin coats and do not wipe off. This will allow it to build up a film. Wiping it off leaves more of a penetrating oil type of appearance, which is probably not what you want. Scuffing the surface with 320 or 400 grit sandpaper will be good between coats and it will help to "level" the finish as you build it up.
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Jonathan Cressman
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Re: Acoustic guitar Finishing advice

Post by Jonathan Cressman »

Great, thanks Barry, this has helped a lot!

Carl Dickinson
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Re: Acoustic guitar Finishing advice

Post by Carl Dickinson »

I use it for necks. I like the feel it leaves. I usually go to 320 on the surface prep and use a finishing synthetic steel wool pad after each 3 coats, applying 12 to 20 coats in all. Stop when it feels good to you.

Alan Carruth
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Re: Acoustic guitar Finishing advice

Post by Alan Carruth »

From what I've read going finer than 220 doesn't improve the wood surface; the sanding scratches are about the same size as the wood cells at that point. My experience bears that out. Finer paper has more of a tendency to clog on wood, which produces a worse surface. I like to dry sand between coats with #400; it takes off the nib without removing much finish.

Finishing is ultimately about surface prep; you can't have a better finish than the surface it's on. After all, how much can you hide under .002"-.004" inch of clear finish? Using a sanding block really helps. Try to not round off corners too much; you'll just be more likely to sand through there.

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Barry Daniels
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Re: Acoustic guitar Finishing advice

Post by Barry Daniels »

I agree with the 220 on most wood surfaces to be finished. However, 220 grit scratches in plastic binding and curly maple can still show up under finish so I take those up to 320. Wood surfaces that are not finished like the fretboard and bridge (especially if made from ebony) benefit from sanding up to 600 grit and then buffing/honing with plain paper.
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Bob Orr
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Re: Acoustic guitar Finishing advice

Post by Bob Orr »

Barry Daniels wrote:
Mon Dec 14, 2020 12:21 pm
You do not need pore filler because cedar and cherry are "closed pore" species.

I am not familiar with either of your two finish selections so I can't help you there. But I would recommend that you consider Tru-Oil which is a wipe-on varnish like product that is VERY user friendly. There are tons of discussions on the forum about Tru-Oil which you can search for and read up on.

+1 for Tru oil. If you are not geared up properly for spraying I have found Tru Oil to be very easy to use. Done four guitars and six ukes so far and no issues at all.

Bob Orr
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Re: Acoustic guitar Finishing advice

Post by Bob Orr »

I apply Tru Oil with a rubber like french polishing. A cotton rag filled with a ball of cotton waste. Leaves a nice thin even film.

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Peter Wilcox
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Re: Acoustic guitar Finishing advice

Post by Peter Wilcox »

I just use Tru Oil on necks. I apply it with my bare fingers - leaves a smooth coat and leaves it on the wood, not soaked into the applicator.
Maybe I can't fix it, but I can fix it so no one can fix it

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Karl Wicklund
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Re: Acoustic guitar Finishing advice

Post by Karl Wicklund »

+1 forTru-oil. I love the feel of it.
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Jonathan Cressman
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Re: Acoustic guitar Finishing advice

Post by Jonathan Cressman »

Thanks everybody for all the advice!

As Barry said, my neck is mahogany, and so needs to have grain filled somehow. Now, when I've looked around, I've found a number of people who seem to think that tru oil does a decent job of filling grain itself, and they don't seem to use a separate grain filler.

Any thoughts on using tru-oil by itself vs using a grain filler underneath it for a mahogony neck?

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Barry Daniels
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Re: Acoustic guitar Finishing advice

Post by Barry Daniels »

I have not done this but read a description as follows: Apply the first few coats with a piece of sandpaper. As you move the sandpaper around a sawdust slurry is created which gets forced into the pores. After the pores are filled, start applying coats of Tru-Oil normally to build up a clear finish. You should definitely practice this on a scrap of Mahogany before you commit to the real thing.

I believe that I read this on Birchwood Casey's website, who is the manufacturer of Tru-Oil. However, I can't find it now.
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Alan Carruth
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Re: Acoustic guitar Finishing advice

Post by Alan Carruth »

Sanding in an oil finish does work pretty well as a filler. Use something like #400 wet or dry paper. There will be a fair amount of shrinkage, and it will take some time: oils harden by oxidation and polymerization, and that goes a lot more slowly than solvent evaporation, particularly in thicker layers.

Carl Dickinson
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Re: Acoustic guitar Finishing advice

Post by Carl Dickinson »

As I recall now that's what I did with the 320 paper, sand the first coats into the wood.

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