How to refinish mahogany body?

[casey73]

I picked up a used mahogany aftermarket strat body that I want to build a DIY guitar out of. It's old and has some wear and tear on what I assume is a nitro finish, but does not appear to be stained. I'd like to put a new finish on it.

I've done some simple furniture refinishing in the past and it has turned out well. I've always used polyeurethane for this. But I've never done a guitar refinish and wonder if there is anything I need to consider so I don't screw it up. I don't have any fancy equipment so I'll be using stuff from a spray can, such as Minwax gloss poly.

Also, I looking for an aftermarket neck. If I can't find a used one I like I may get one of the unfinished blanks that are available from many sources. I like gloss finish on my necks, but again, I'd like to know what type of finish will work. I know tung oil is popular with some, but I'm not sure I'd like the feel of it.

Any tips or advice are welcome since I don't have lots of experience with guitar finishes.

[Earl Norton]

Try out a few finishes...see what you like. BTW, tung oil does not dry oily, it is very much like varnish but without the build up.

[David Schwab]

Mahogany has open pores, so if after stripping the body you see open pores (which would mean what ever they use as pore filler came off with the finish, which is likely) you'll need to fill the pores before you finish the body, if you want a smooth flat surface.

Some people like the natural wood look though.

Finishing can be tricky, so I'd suggest picking up a book on it.

http://www.stewmac.com/shop/Books,_p...Finishing.html

[casey73]

Thanks - I did an oil finish on an table long ago, just wasn't sure how it would work with guitar, but apprently is popular with some. I have some scrap mahogany in my garage that I'll do with a test run.

[casey73]

Thanks for the tip. I'll look around for some info at the local library. It is hit and miss on the web.

[Rob Mercure]

Actually pure tung oil can be quite "oily" for some time after application - most of the products sold as "tung oil" have chemical driers and other additives in addition to the tung oil. Probably isn't that important unless you're going to chew on the neck (pure tung oil is suitable for a food surfaces finish while modified tung isn't as the "driers" are metal salts for the largest part).

You might try french polishing the neck with shellac. While shellac isn't as impact resistant as poly and will cloud if wet by water you can easily clean up small nicks and clouds with alcohol. The finish will be dry and ready to use in minutes and is about as smooth and "friendly" as you could want. If you've never "repaired" a shellac finish it's almost a "miracle" as a pad wetted down with alcohol and a few swipes restores a finish in minutes - can be done on the road between sets!

But make sure to make up your own shellac solution of buy one with a date on the can no longer than three months old. Dry shellac will last forever but once mixed is only good for a few months. Beware of any type that claims an infinite time as it will not dry as hard and glassy as you want.

Rob

[Paul P]

Won't shellac get sort of soft and gummy in hot weather ? I don't think
it's the greatest water barrier either, wet glasses will leave rings, which
might be a problem with sweaty hands.

A finish that I've used for years on just about everything I make is a
mixture of 1/3 pure tung oil (from a place like LeeValley), 1/3 paint thinner,
and 1/3 satin polyurethane. With a flannel cloth just wipe it on really wet
and rub it in, wait an bit, then wipe it all off. Rub and polish it until it feels
dry to the touch then let it dry. Repeat the next day. There shouldn't be
much of a layer at all, like there was nothing there really, but so smooth
and fairly waterproof. You could apply more coats if you wanted a thicker
coating but I don't. This doesn' t fill the pores but I like it like that. I think
I got the recipe from an old Tage Frid woodworking book.

I've tried pure tung oil but that keeps seeping out for months and will grow
white hairs if you leave the item in a damp environment like a basement or
garage.

Paul P

[Rob Mercure]

Not at all! After all shellac was the finish of choice for a long time and really expensive guitars - especially classical - come with "French polished" finish. Shellac is much like nitrocellulose lacquer and suffers from being a little bit brittle (which can easily be fixec by remelting the finish. As can any water clouding which doesn't happen from sweaty hands but from stranding water. No instrument - 'cept possibly an Ovation - will survive covered with standing water.

Pure tung oil will produce a "gummy" finish until if fully polymerizes (actually I like pure tung but it provides less protection than shellac and takes far too long to dry). And polyurethane will produce a softer finish and under some conditions - exposure to environmental chemicals from air pollution, solvents used in case manufacturs, etc., - will melt. I refinished a guitar neck that was poly which had, during a 4 months warm weather storage, melted into the carpet like material lining the case. T'was a real pain to remove the finish. I guess this is another reason that I like shellac cuz if it did for some reason melt into cloth the mess can be easily removed by alcohol. Now if the player is a heavy drinker of straight vodka or grain alcohol I'd probably recommend nitrocellulose (must be sprayed though) or poly but otherwise shellac is about the "friendliest" and most environmentally benign finish you can find (unless sacrificing millions of lac beetles to make it is unconscionable to you and if so get rid of your boots and leather strap and become a Jain with a cloth across your mouth [and I wonder how Jains justify the loss of millions of bacteria when they take a poop]).

Rob

[David Schwab]

If you want to do an oil finish, get a oil varnish blend, like Watco Danish oil, or something similar. They dry nice and hard.. well hard for oil. But they do dry. You can build them up to a nice sheen.

I did a korina and pau ferro fretless bass with Watco, and after 12 years it still looks good. Needs a new coat every now and then.

I also used watco under the lacquer on some of my basses. I gave them a wipe coat to make the wood pop, and let them dry a week, and then sanded and sprayed catalyzed nitro.

A lot of luthiers swear by Tru-Oil, which is a polymerizing linseed oil originally made for gun stocks.

[jack briggs]

Won't shellac get sort of soft and gummy in hot weather ? I don't think
it's the greatest water barrier either, wet glasses will leave rings, which
might be a problem with sweaty hands.

A finish that I've used for years on just about everything I make is a
mixture of 1/3 pure tung oil (from a place like LeeValley), 1/3 paint thinner,
and 1/3 satin polyurethane. With a flannel cloth just wipe it on really wet
and rub it in, wait an bit, then wipe it all off. Rub and polish it until it feels
dry to the touch then let it dry. Repeat the next day. There shouldn't be
much of a layer at all, like there was nothing there really, but so smooth
and fairly waterproof. You could apply more coats if you wanted a thicker
coating but I don't. This doesn' t fill the pores but I like it like that. I think
I got the recipe from an old Tage Frid woodworking book.

I've tried pure tung oil but that keeps seeping out for months and will grow
white hairs if you leave the item in a damp environment like a basement or
garage.

Paul P

Pure tung oil won't polymerize on its own. You usually would thin it with mineral spirits or turpentine, which helps to polymerize.

French polish shellac really takes years to fully cure, so it certainly can get gummy from even the heat of your hand until such time. Owners of very high end classical guitars sometimes will not even handle them for many months from new until the finish hardens enough to prevent printing the finish.

Nitro hardens a little quicker, but still takes months and years for all the solvents to fully evaporate from the film.

My suggestion would be a tung oil finish cut with mineral spirits, if you want one that feels really organic and natural and don't want to wait a long time for curing. 1 part tung oil to 1 part mineral spirits wiped liberally on the wood to flood the surface, let sit for a few minutes then wiped off, repeated about 3 times several hours apart, then let dry for 3 days. At this time you'd hand buff with a clean rag and you're good to go.

[Rob Mercure]

Mr. Briggs,

It's obvious that youve not worked with fresh shellac - and I mean fresh in both that the insect exoskeletons have been harvested fast and that the shellac cut has been freshly made. Shellac isn't a polymerizing finish but a solvent release one as just as soon as the alcohol evaporates - and you have to use anhydrous alcohol - the finish hardens about as much as it can. Perhaps if one were to spray shellac in a humid atmosphere it might need some time but I've built up layers on a neck and played on the finish with a "conservative" 1/2 hour drying time in the summer. Nitrocellulose is also solvent release and only gets soft and gummy when there is some other solvent present - certain localities have enough industrial emmissions to cause troubles but if your air if clean the finish dries right off. Where do you live?

There is once confounding factor that might be confusing thing and that is that there are some French Polishing "recipes" that recommend adding materials other than shellac and alcohol - I'd almost forgotten these and they are from the days before finishes were well understood and and might have started a rumor that FP finished need time before handling or have led some luthier to mix up such a recipe. How sad. I've French Polished table tops - that I expected to have abuse from alcohol - and used them in 20 minutes and they were so hard that I could lean on them open handed and not leave a print.

All I can suggest is to buy a few ounces of good shellac - Belhem used to sell a high quality orange (the "clear" has been chemically bleached and is weaker) and mix it up yourself with freshly opened anhydrous denatured ethanol on a day of less than 30% relative humidity and coat a sample "neck" or two - shellac is the only quick finish for a hard non porous wood.

Rob

[jack briggs]

Mr. Briggs,

It's obvious that youve not worked with fresh shellac - and I mean fresh in both that the insect exoskeletons have been harvested fast and that the shellac cut has been freshly made. Shellac isn't a polymerizing finish but a solvent release one as just as soon as the alcohol evaporates - and you have to use anhydrous alcohol - the finish hardens about as much as it can. Perhaps if one were to spray shellac in a humid atmosphere it might need some time but I've built up layers on a neck and played on the finish with a "conservative" 1/2 hour drying time in the summer. Nitrocellulose is also solvent release and only gets soft and gummy when there is some other solvent present - certain localities have enough industrial emmissions to cause troubles but if your air if clean the finish dries right off. Where do you live?

There is once confounding factor that might be confusing thing and that is that there are some French Polishing "recipes" that recommend adding materials other than shellac and alcohol - I'd almost forgotten these and they are from the days before finishes were well understood and and might have started a rumor that FP finished need time before handling or have led some luthier to mix up such a recipe. How sad. I've French Polished table tops - that I expected to have abuse from alcohol - and used them in 20 minutes and they were so hard that I could lean on them open handed and not leave a print.

All I can suggest is to buy a few ounces of good shellac - Belhem used to sell a high quality orange (the "clear" has been chemically bleached and is weaker) and mix it up yourself with freshly opened anhydrous denatured ethanol on a day of less than 30% relative humidity and coat a sample "neck" or two - shellac is the only quick finish for a hard non porous wood.

Rob

Mr. Mercure,


I have worked with fresh shellac for years. I wonder how much you have. Behlen's (not Behlem) is far from the best flake shellac out there. In fact I have most of a pound of their "Blonde" that I'd sell to you cheap. It's not as good as others. Currently the best I've used is from Hock. I used to buy from Star Finishing in Mendocino, CA who offered about a dozen different shades of flaked shellac, but they seem to have gone belly up.

Frech polish is not only a technique, but a recipe that has oil added to the shellac. It is not the same as straight shellac. French Polish finishes do polymerize due to the added oil and the heat from the rubbing action. There's a whole library of info on this subject that I won't go into. As for French Polish finishes not hardening quickly, you're probably used to a recipe that's more for furniture. And most people don't wear a table under their arm for any amount of time - not a good analogy.

Ask anyone who owns a classical with a Frenched finish - they print easily for the first couple of years. It's a fact. Many classical players will let their instruments harden for months before even putting them into use.

If you'll go back to my post which I assume you're referring to, I made mention that tung oil finishes don't polymerize on their own. How did you get shellac from that? I know shellac isn't a polymerizing finish - that is until it has the addition of an oil making it into a French polish finish.

Remember - Google is your friend. All kinds of info on this subject.

[David Schwab]

A good source for finishing info is the Musical Instrument Makers Forum

http://www.mimf.com

They have a vast library of info.

[Rob Mercure]

To Jack Briggs (don't want the "Mr." to be off putting - seems to have hit a bad note last time):

Sorry to take so long to respond - computer signal (WiFi) has been flakey and I wanted to do some research. So, as to French Polishing we're both right but you're more right <grin>. What I mean is that the most common method used oil and I concede that. But the method I learned from Fine Woodworking magazine didn't involve alcohol - but is primarly used for touch up and I adapted it to new finishing (part of my research was to dig up one of the compendium of Fine Woodworking articles that had been put together called "Finishing" and reread the article - I've had the book since it was published in the early 1980s). Over the years I had forgotten most of the technique as I'd never worked with oils myself. So, believe it or don't, you can build up a French Polish without oil but it is more difficult and I'm sure that I've not built up the thickness that you've been able to achieve with the more common method - I have used this on necks and it does dry very quickly. So I apologize for any misunderstnding.

Rob

[jack briggs]

Rob,

No problem, man. I realize also that there are differing uses and techniques. I was just referring to the normal use as applies to lutherie and guitars specifically.

I,in fact use shellac on almost every guitar top that I finish, but just straight (~2lb. cut) as you've described. Although I "French" it on with a pad I don't really refer to it as French Polish under lacquer, as I tend to think of French Polish as not only the procedure, but the recipe with added oil.

All is good.



Cheers,