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PostPosted: Tue Jul 03, 2018 9:11 am 
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Koa
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I'm in the process of building my first acoustic. My situation is such that it is not possible to purchase a dehumidifier. In the past, on restorations I have done, when replacing a top/back, I have always done this in winter, after my furnace has kicked in a while, and humidity has dropped and remained in mid thirties/forties RH.
If I do this for this build, it will be early summer 2019 before it gets a finish.
My thinking is to build basically a "guitar humidor", a sealed box deep enough, wide enough and long enough to store the top and back wood, or alternatively, an entire guitar. I would use desiccants to bring the RH within this box to a proper humidity level and keep it there.
The question is, is it the humidity in the environment where you are bracing, or the level of humidity/moisture within the wood itself? In other words, if I keep the wood stored at around 40% RH, but remove it from that environment long enough to brace it (RH in that environment would be 57-63 RH, generally), will this work?
I know that a lot of times I see advice that if you have no way to control humidity it is possible to build anyway, as long as the instrument remains in the same environment. But I'm in Virginia, and the difference between winter and summer here IMO precludes that idea.

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PostPosted: Tue Jul 03, 2018 9:44 am 
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Seen people using a box with a light bulb inside connected to a humidistat, but taking the wood out into a different environment will result in the wood moving very quickly.

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PostPosted: Tue Jul 03, 2018 10:58 am 
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Mike--

A few thoughts for you:

1. I am in West Virginia (i.e., the former poor part of Virginia), and I know the hard way that the summer to winter humidity swings are intense where you and I live. You really need to do something to keep the moisture content of the guitar wood down at this time of year. If you put the box together with the relative humidity what it is right now, top cracks in the winter are not just possible, they are probable. Again, I know this the hard way.

2. There is a Robbie O'Brien video on YouTube about the idea of having a smaller part of your shop that has a controlled RH level, and leaving the rest of the shop to fluctuate with the seasons. You should watch that. People do it, including the whole drying cabinet idea. Here is a product you might want to look into, if you want to build a drying cabinet:

http://www.leevalley.com/us/Garden/page ... 60&p=69378

3. Personally, I feel I need to control the whole shop. But, that's just me.

4. You need to get accurate RH measurements, which is not something I would assume is happening right now unless you are far ahead of the curve. This is a sneakier problem than you probably think it is. Common hygrometers can be way off.

Good luck!


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PostPosted: Tue Jul 03, 2018 11:08 am 
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Thanks, gentlemen. I have some "figuring" to do.
Don, my shop is 10' x 10'. If I could afford a dehumidifier it would not be difficult to keep it where I need it.
Unfortunately, my budget is not there. "Shoestring" does not begin to describe it.
I will look around at local flea markets and try to find a used a/c unit. If I run one of those on low, it might be enough to do the job.
I tried the desiccants. 4 large ones could not drop the humidity past 48 %, nor keep it there for any appreciable time.
And you are correct; I'm not even certain that reading is correct, because I'm using a $30 digital "weather station" for those readings.
Last resort I will just do everything else I can, and wait for the onset of winter. not ideal, but it will work.
The thing is, I am not building to sell; I'm a beginner at acoustic building. But I don't want humidity problems in the winter with my personal guitars any more than the next player. And should I choose to "gift" anything in the future, I don't want my friends pulling their hair out for the same reasons.
I would love to know how the old timers did this before the age of electricity, humidifiers/dehumidifiers, etc.

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PostPosted: Tue Jul 03, 2018 11:16 am 
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Mike,
You should have a look here for a Box idea.
https://classicalguitardelcamp.com/view ... a420404b59

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These users thanked the author Jim Watts for the post (total 2): DennisK (Tue Jul 03, 2018 12:42 pm) • Mike Baker (Tue Jul 03, 2018 11:25 am)
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PostPosted: Tue Jul 03, 2018 12:42 pm 
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Mike Baker wrote:
The question is, is it the humidity in the environment where you are bracing, or the level of humidity/moisture within the wood itself? In other words, if I keep the wood stored at around 40% RH, but remove it from that environment long enough to brace it (RH in that environment would be 57-63 RH, generally), will this work?

What matters is the moisture in the wood itself. However, thin guitar woods respond to the environment very quickly (most of the movement is done within an hour if both sides are exposed to the air).

If your brace gluing strategy is to do it in multiple stages, you should make the hot box big enough for the soundboard to fit inside with clamps on. Even if you glue all the braces at once, the soundboard may expand before the glue is dry. It's possible that if you use hot hide glue and glue all braces at once, that the glue will grab tight enough in the first couple minutes to resist the soundboard expansion, even when it's not entirely dry.

Assuming you're using a typical target humidity somewhere in the 40-50% range, then dry the wood 10-20% below the target, and acclimate up. If you acclimate from high humidity down to the target, the wood will actually have a fair bit more moisture in it than if you dry it out and acclimate up to the same RH%. This torments a lot of new builders. Brace at 45%, then it gets cold outside, heat comes on, humidity tanks, and the plate turns inside out. Then they get the humidity back up, and it's still inside out. Usually they end up chiseling off the braces and redoing it.

The problem is that it was actually braced at much higher moisture content than they thought. If they'd acclimated up in the first place, then it would return to normal. I've personally verified this. The effect is called hysteresis. I'd estimate that acclimating down to 35% is equivalent to acclimating up to 45%. So you could acclimate down if you use 35% as your bracing level.



These users thanked the author DennisK for the post (total 2): CraigSz (Sat Jul 07, 2018 10:27 pm) • Mike Baker (Tue Jul 03, 2018 12:48 pm)
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PostPosted: Tue Jul 03, 2018 1:53 pm 
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You might consider baking the top too. 200 deg F for one hour and serve with a nice side of hot hide glue.



These users thanked the author jfmckenna for the post (total 2): Mike Baker (Wed Jul 04, 2018 7:04 am) • Ken McKay (Tue Jul 03, 2018 4:06 pm)
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PostPosted: Tue Jul 03, 2018 2:06 pm 
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I've used a hot box before and it works fairly well. It only takes a few minutes outside the box to glue on braces if you have everything ready to go. I made mine out of a large wall cabinet with a couple of light bulbs. I monitored things with an inexpensive hygrometer and didn't try to hold it to a specific percentage, but tried to keep it in the range of 35% to 55% R.H..
I've upgraded things to a humidifier in a closet - a slightly larger space, and it actually dries the air rather than raising the temperature to lower the R.H.. But I still have to keeps parts in the closet and only have them out for a short duration while I glue braces and such.
When you figure out what needs to be done under humidity controlled conditions, and what can be done in ambient conditions you find the majority of the work doesn't require perfect R.H. control.You don't have to run the hot box 24/7. As a hobbyist I'll deal with the limitations for the cost savings. If I was a pro shop I would want at least a room sized enclosure humidity controlled.


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PostPosted: Tue Jul 03, 2018 2:12 pm 
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FWIW, I've been building for about 20 years now, and I've spent 40$ on dehumidifier so far.

The first one was free, and the second was 40$ at a flea market, as you've already self suggested. My RH room is 10x12 and it's easy to keep controlled during high humidity swings.

So I'd take an intent look at what you can find out there, you can probably get what you need...


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PostPosted: Tue Jul 03, 2018 7:04 pm 
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+1 I try to find a used one. Generally speaking, the cleaner it looks, the least use it has probably had. Look for a clean bucket and clean filter. We have pawn shops around here they give you a 30 day guarantee which is handy because you can't tell if it works until you have it on for a while.


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PostPosted: Wed Jul 04, 2018 6:14 am 
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I have considered a used one if I can find it. What has thrown me off of that is remembering seeing threads about dehumidifier recalls and fire. I live in a trailer. The word fire carries extra emphasis.

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PostPosted: Wed Jul 04, 2018 6:59 am 
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Some of the small dehumidifiers have a short lifespan. If you buy "used" make sure it is working. I bought a new Maytag - it worked for about a year - not a great investment. Apparently, the moisture makes things fail (rust and corrosion)
The next one I bought from an estate sale for a few bucks - so far so good, but I only run it when I am doing things that require humidity control.



These users thanked the author Clay S. for the post: Pmaj7 (Wed Jul 04, 2018 9:07 am)
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PostPosted: Wed Jul 04, 2018 7:03 am 
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Koa
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Clay S. wrote:
Some of the small dehumidifiers have a short lifespan. If you buy "used" make sure it is working. I bought a new Maytag - it worked for about a year - not a great investment. Apparently, the moisture makes things fail (rust and corrosion)


Ain't that a hoot! Looking at prices at my local Lowes, that right there... idunno

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