a couple questions of wood and humidity

I am about to start building a tenor uke for a friend of mine who lives in south Florida and I'm a little worried about the heat and humidity down there.
Is there anything I can do, preemtively, to keep the uke from coming apart years down the road?
I'm going with through holes into the soundbox for the strings, so I'm not worried about the bridge, but should I be worried about the rest?
Does anyone put finish on the insides of their instruments to seal the wood?

Also, I'm thinking of using some beautiful Curly Mango that I found online from Hawaiian Hardwoods.
Can anyone tell me if this is a terribly difficult wood to work with as far as bending and such?

~Fred

Hi, I live in Tampa, it gets hot here but no hotter then anywhere else, we just spend more time in the 90's... i guess we are hotter then Boston and the north east...

Do not finish the inside of the instrument!... my understanding is it will kill the sound. Someone else please conform this.
As far as humidity, it is my understanding that it is much harder to go from high humidity to low, then low to high... If I understand the theory, you want the instrument to take on a little moisture once it has been built. Luther's always say to build instruments with wood at around 6% mc. I am here to tell you that wood in Florida will basically never drop below 8% and rarely below 10% unless kept in a well climate controlled area. To be honest I think the mc is not as important as many make it out to be, within reason. Instruments travel all over the world through all different weather conditions and do not fall apart. This may simply be naivety on my part.

You can take wood that has been kiln dried to 6% and it will go right back to 8-10% in short order... I have a stack of red oak that was kiln dried to 6% and then storred outside covered and it sits at a very comfortable 9-10% pretty much year round .

What glue are you planning to use? My first build I used liquid hide glue (i know not the same as HHG) and it was not a good idea. I would think that HHG would work here, but i have not tried it, and i would definitely not feel good about bringing my instrument out and taking it with me in the car in the summer when it is 130* in my car for a few minutes and will stay in the 90s in the car for quite a while, and that is with the ac blasting... I have been know to use my car as a kiln in the summer...

There are several issues at stake when discussing wood in this context. One, tonewood needs to be dried to a constant MC. That MC will vary on the climate in which it is dried but the target seems to be 8-10%. If that isn't done then the instrument will most likely crack as it dries. So dry it before building. Second, instruments do go all over the world and will not crack or split unless exposed to some pretty extreme humidity and/or temperature changes but this can often be resolved with the use of humidifiers. Structural issues aside, if the MC can't be maintained then the instrument will shrink or swell and the intonation and/or action may make it unplayable.

Mango is nice to work with and unless really curly should be pretty easy to bend with a blanket bender. I have had good luck with the mango I got from Steve at HH. And it sounds great when done!

Grammar

I agree with mrhandy.

Don't finish the inside of a conventional acoustic ukulele. If this was a workable idea, every builder would be doing it. (I did work with a brilliant guitar luthier who was toying with the idea of oiling the inside of his instruments)

mrhandy is also correct saying that the wood must be properly prepared before your build. He's very realistic about humidity, telling you it will be nearly impossible to attain your ultimate humidity goal unless you invest in rather prohibitive measures in your Florida shop. As always, you can only do your best. Perhaps you will have opportunity to build when the wood and the shop conditions are at their most cooperative. Timing may help, but Mother Nature will have her say.

Yes, instruments travel all over the world through all different weather conditions. But, they do eventually come undone.

Your question seemed more about the wood than glue joints, though. I think this is the right question. The humidity problems almost always effect the wood before the glue joints. On old instruments you'll usually see cracks in the wood before the joints start breaking down (barring poor glue joints). The reason you prep the wood is that if it contains too much moisture at build time, the extracellular moisture will dry out when as it is sufficiently exposed drier conditions and the wood will shrink. Sometimes you will see a top or back come loose in one area or another. But, this is caused at least in part by the largest boards shrinking so much that they pull the glue joints apart. How much will your material shrink and how quickly? Way too many factors to discuss here. But, remember that master luthiers have been building ukuleles in Hawaii for more than a hundred years. Perhaps, if you are building instruments that will be leaving the tropics, you would want to limit features that you think might be problematic. If you build ukuleles with through holes, see if the wood starts to crack around these holes in sixty or eighty years. This probably won't happen, though. The through holes will be relatively well reinforced by your bridge and bracing material. But if it is a problem, maybe you'll want to do something different.

mrhandy also mentions he wasn't happy with liquid hide glue. I've never heard anything good about the stuff. It is in no way a substitute for hot hide glue, which is excellent old-world wood glue. But, keep in mind that hot hide glue requires a great deal of experience. You have to continually, throughout your gluing processes, monitor the glue consistency, and you must work fast for most uses. I worked with hot hide glue for twenty five years and I was beginning to get pretty good with it. If you have questions about glues I would recommend reading up on the modern wood glues. Most wood glue, tite-bond, carpenter's glues will do everything you need, and do it very well. Easy to use and should last a lifetime.

Historic note I find interesting: Bluthner Piano manufacturers in Leipzig used to (may still) offer all their models built for "normal" conditions, for semi-tropical, or tropical conditions. The semi-tropical and tropical ones utilized many more screws to secure the soundboards. The tropical instruments used no felt between the strings and the plate, to slow the rusting process.

Maybe it's a Hawaiian thing but almost everyone I know here applies at least some finish to the interior.
I have found non figured mango a dream to bend. I had some extremely curly mango that I couldn't bend at all. The grain was so wild it crumbled like potato chips.
Just make sure your customer is aware of the climate/humidity needs of the instrument. Florida and Hawaii share a similar environment although we don't have the wide swings Florida does. You'll probably be OK. But lack of humidity may be real problem. Having lived in Florida for a short time, I know that every home is air conditioned which can suck a lot of moisture out of the house. And unless he is in south FL, the winters can get awfully cold and dry as well.

I think it was one of the Oz guys who said recently that he finishes his interiors, with shellac, if I recall. This does make some sense. In my boat building days, we wouldn't even consider finishing just one side of a piece of wood because setting up a situation where moisture absorption is unequal is the straight road to a warped board. It's hazardous to draw parallels between boats and ukulele just because both are made out of wood but this may be one case where there is a similarity.

saltytri said:

I think it was one of the Oz guys who said recently that he finishes his interiors, with shellac, if I recall. This does make some sense. In my boat building days, we wouldn't even consider finishing just one side of a piece of wood because setting up a situation where moisture absorption is unequal is the straight road to a warped board. It's hazardous to draw parallels between boats and ukulele just because both are made out of wood but this may be one case where there is a similarity.

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In my mind you are absolutely right. Take a thin board and apply a finish to one side only, then set it outdoors for a while and see what happens.

Thank you, everyone. This is all great information; exactly what I was looking for.
I live in Wisconsin, so my shop this time of year is pretty dry. The guy who is buying the uke lives just south of Tampa, so I was wondering about the humidity difference. But as someone said above, people have been making and shipping ukes for a long time, so I wont worry too much about it.
Perhaps I will try a thin layer of shellac on the inside. Maybe applied with a rag?
The guy who is buying it is a professional musician and a fantastic ukulele player, so I'm hoping he knows how to care for it.

Thanks also for the advice on the mango wood. I've only bent mahogany so far, so I'm a bit nervous to try some curly wood.
I assume you shouldn't soak curly wood, only keep it damp during bending. Does that sound right?

I do not believe finishing the inside of an instrument with a thin coat of shellac will harm the sound in any way.

should I thin the shellac with something, or will that compromise the glue joints?

I subscribe to the notion of what you do to one side of a board, you also do to the other.

All my instruments get shellac on the inside. It does not affect the sound in any way that anyone I've met could hear. What it does do is buffer the instrument from quick and drastic swings in relative humidity. Short of getting caught in a bar fight with your uke, that is the most hazardous thing for them.

Also since I use hide glue to construct my instruments, using shellac to seal the inside also protects the glue joints from prolonged high humidity. I've never seen it happen, but have heard from another luthier that hide glue joints can show signs of fungus growing on them in high humidity (presumably from poor glue clean up) and shellac stops this.

You can make the shellac as thin, or thick as you like. It will not compromise any glue joint. Solvent is alcohol. Same as is used to make it. I tend to make my shellac up fairly thin but apply 2 or 3 coats.

Once again the Hide Glue myths are out. Hot Hide Glue is not difficult to use. It requires the user to be informed on how to use it. There is lots of info out there on its use. The grand total of equipment needed runs to: a baby bottle warmer and an empty baby food jar.

If you think HHG is complicated, try building a uke.

There may be reasons not to use HHG but the reason shound never be "because it's too hard"

Thanks again guys. I will definately try a light coat of shellac. Right now I'm using Titebond red cap, so I assume that's all compatible.

Hopefully, my mango will survive the bending process and I will have something nice to show you all!

Boy there is lots of interesting information in this thread. I may have to give the shellac on the inside a go as well... I have been told, by someone that I now cannot remember, to never finish the inside of the instrument... I agree that it makes a lot of sense to do so as far as moisture absorption goes.

Another thing to remember about wood movement, is that the majority of the way quarter sawn wood shrinks and expands in in thickness, where as flat sawn wood shrinks and expands in width. This is a major reason we use Quarter sawn wood in instruments instead of flat.

mrhandy said:

Boy there is lots of interesting information in this thread. I may have to give the shellac on the inside a go as well... I have been told, by someone that I now cannot remember, to never finish the inside of the instrument... I agree that it makes a lot of sense to do so as far as moisture absorption goes.

Another thing to remember about wood movement, is that the majority of the way quarter sawn wood shrinks and expands in in thickness, where as flat sawn wood shrinks and expands in width. This is a major reason we use Quarter sawn wood in instruments instead of flat.

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Never heard about quartered wood changing dimension in thickness before. All wood tends to change more across the grain (width) than along the grain (length). Standard advice is to stabilize your wood around 40% humidity. More humidity after the build seems OK, though I often think I can hear the "water" in an instrument when humidity gets really high. It's up to the owner to protect an instrument from really dry situations. Drastic changes in humidity may change the action a bit, but ukes are so small that its hard to imagine a top crack forming. (I've seen it, but the conditions must have been extreme) Another good reason for radiused tops, though, even if a 25' radius hardly adds up to much in a soprano.

jcalkin said:

Never heard about quartered wood changing dimension in thickness before. All wood tends to change more across the grain (width) than along the grain (length). .

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Basically as I understand it from a furniture standpoint, wood shrinks the most in line with the grain. This would mean that in a flat sawn board it will move more in width then in thickness (it does move in both directions)... in a QS board the prodomant movement is in thickness, however because of the dimentions of a board it may seem to shrink more in width, however the percentage of movement will be greater in thickenss. I hope that makes sense. The basic statement is that because the greater percentage of movement is reduced by moveing it to the thinner dimention of the board, it makes the board more stable... wood is also generally stiffer in a QS board thus making it more suited to thin applications.

Interesting discussion. Of all the string instruments that I have repaired over the years, I can only remember one classical guitar that had shellac finish on the inside. The back and sides were rosewood that had multiple cracks, some so wide you could slip and envelope through. The guitar was made in the south, maybe Mexico. The inside finish didn't help it one iota. If the wood isn't properly cured to 6-7% moisture content before it is used, it is going to shrink. The wood used in this guitar wasn't Indian, but more like Cocobola or something similar. Figured rosewoods are notorious for shrinking anyway.

I would suggest those of you who live in humid, warm climates, build a separate small room to store your wood in and dehumidify until the wood is at 6%. I would never build a uke or guitar or violin for that matter with the wood at 10% moisture. Trouble for sure. And since I brought up violins, these are put together with HHG exclusively and I have never seen one that had finish applied to the inside. Maybe some builders do apply a thin shellac to the inside, but I have never seen it done.

Concerning the Shellac on the inside, a lot of great steel string guitar builders do this......Ervin Somogyi, Ray Kraut, Michi Matsuda, and Jason Kostal just to name a few. I think they use shellac with laquer thinner 50/50. Its basically just a wash coat. The Shellac wont seal the moisture out, but it will slow the absorption and protect the instrument from drastic changes in humidity. It could also make the top stiffer without adding any measurable mass to the plate ......Why haven't I tried this yet? LOL