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Hi, I am a beginner to guitar building. I have successfully completed 2 solid body electrics and now have bought my first acoustic kit. Since I do not have a lot of time to build my guitar it may take me several years to complete. My work shop is in the basement and I have read that I should not build an acoustic if the humidity fluctuates more than 10%. say 35 to 45%. Although I have a dehumidifier and the basement does not get above 55% in the summer or below 35% in the winter should I be concerned? I understand that the wood expands and contracts at different moisture levels but will this variation really affect my building?

Jim

Your situation is not perfect, but if you take steps to hold/control the
shape of the parts, you should be alright, IMHO. IE, keep the sides in a
mold with inside cauls to hold the shape, Join the back and top on as
soon as you can after gluing the braces. If that's not possible, at least
keep the top and back in radius dishes in a go-bar deck, or held down
with weights to hold their shape after bracing. I'd try not to attach the
top and back during your highest RH periods. Wait for a couple of weeks
after the humidity settles back into the recommended zone before
gluing the top and back on.

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Gene

Politicians and diapers must be changed often, and for the same reason- Mark Twain

If you have a dehumidifier, is there a reason you expect/allow large swings in RH? Is the dehumidifier not large enough to keep up in the summer months? Humidifiers are relatively cheap, so you can increase RH cheaply when needed. You will find building is much easier in a controlled environment. That said, there is no reason that you can't build even if you do experience swing in RH of 10% or more. You just have to be very aware of RH when you build. Folks have been building guitars or similar instruments without dehumidifiers for a very long time. As mentioned in the previous post, brace when you RH is low (35% is usually what I shoot for). Set aside a full weekend to brace the top and back and immediately glue them to the sides. I try very hard to maintain steady RH, but I have been the victim of warping after bracing due to increased RH. Not fun. It doesn't take long or much of a shift in RH to cause problems, and it takes a lot longer for the wood to lose the excess moisture that it took to gain it.

Aaron

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Aaron Craig

Thanks you both for your input on this topic. I will be purchasing a RH meter to more closely monitor the work area and will take the assembly advice you both recommended. I furthermore will move the dehumidifier into my work shop veruss the general bacement area to keep better control.

I am new to the forum and were excited about the timely response.

Jim

Really? Brace at a relative humidity of 35%? Seems low according to my research. I thought between 40 and 60% is ideal. Neither too humid or too dry.

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"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

Nickton,

Yep, 35% is what I shoot for, but anything between 35-40% will do. If you do some searching on the forum, I don't believe I'm alone in this practice. I personally will not brace in an environment above 45% RH. Here in the Midwest, we see large swings in RH. In summer it can be 90% easily, and in the winter it can easily fall below 30%. There is no real drawback to bracing and closing the box in a low humidity environment. The same cannot be said of bracing and closing the box in a high humidity environment.

I build with a radius on both top and back, so there is room for the wood to rise if expansion occurs in more humid weather (though you might need to re-adjust string action; some make a summer and winter saddle for this purpose). If you brace at say 50% RH using a 25' radius and the guitar, after assembly, is subjected to a lower RH environment, the 25' radius will quickly disappear. After your radius disappears, the only way for the wood to contract further is by cracking.

So, know your present RH. Know the seasonal trends for RH in your geographical region. Know the seasonal trends for the RH in any other region you believe your guitars might spend any significant amount of time. Then, brace and close the box when RH is at the low range of any relevant seasonal trend.

Aaron

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Aaron Craig

I keep my humidifier in my instrument room (which includes guitars, other string instruments, and percussion instruments) at 45% on advice of people who've worked in boutique guitar shops. Knock on wood, but it's suited me well so far with no tuning issues or problems with binding or top bellying for about a year straight.

Here's a slightly different perspective.

I accept the target humidity level of 35% - 45% for building, but I've found it impossible to keep my shop to that target year - round. It will stay that dry in winter, when the challenge is keeping the humidity UP. Summtime, my shop tends to go closer to 60%, even with A/C running.

So, the way I've dealt with my situation is to tackle certain jobs ONLY when humidity is close to that range (35 - 45% RH). There are a lot of tasks one can do in different humidty conditions, such as thickness tops, backs and sides, laminate necks, join backs, join tops, fabricate bridges, necks, saddles, nuts, do setup, build jigs, etc., etc. And finishing work takes longer, but I haven't had trouble spraying finish in higher humidity (I know that nitro doesn't like it, but knock on wood, no troubles with water - based finishes to date).

I am very careful to 1) glue braces to tops, and 2) close the box only when the humidity is right. Otherwise you end up with potato chips and sunken tops. If I have to do these things in summer, I'll run two dehumidifiers in the shop for at least a week to try to acclimate the wood. And make sure to close the box very soon after gluing braces on back and/or top.

Takes me a long time to build a guitar, so this seems to work for me.

Make sense? Am I playing with fire here? Seems to work so far.

That's a great way to handle the issue if your build schedule allows it. Guitars and other stringed instruments were made for centuries before we had handy little dehumidifiers, and there are plenty of stories of master luthiers of yore watching the weather to complete certain tasks only when conditions were ideal.

One thing you probably do but didn't specifically mention in your post, is try to close your box as soon after bracing the top and back as possible. Try to set aside a full weekend to brace, voice your top and back, and close the box. Humidity swings do weird things to braced plates quickly. Also, if you think your humidity might change after bracing, it is wise to keep them in their hollow forms in your go-bar deck (or just put weights on them in the hollow forms if you need to use the deck for something else.

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Aaron Craig

Excellent point - I learned that one the hard way, too. Potato chips aren't much good for building. That seems to be the most sensitive step in the process, in terms of humidity.