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Hey guys. I'm starting my first guitar build with a neighbour. Actually building 3 so we have a guitar to make mistakes on. We're total rookies, learning from the Kinkade book, and the internet. It's been about a year and a half of researching and building jigs etc, but we finally started with our rosettes on the holidays, and have now braced and voiced the backs with the appropriate arch in a go-bar press very successfully, and are about to brace the tops. Unfortunately I am limited to a VERY small shop (<100sq ft), which is manageable, but the kicker is that it's the only usable room I have for a shop, and it contains my sump hole.

I know its not ideal (far from it), but its all I have. I run a dehumidifier non stop, have sealed the hole somewhat, (will be improving the seal as best I can b4 i glue the top bracing) but I can NOT get the RH below about 48%. The rest of my house is between 60-70%

Am I understanding this correctly, that it's the RH at the time of build or glueing that matters, and that increasing the RH after is not as critical as lowering the RH later? The backs seem to be quite stable (Indian Rosewood and Zircote). I live in southern ontario, and it's always pretty humid here, I'm just concerned that I'm screwed if I can't get the RH down to 30-40% for glueing, or I'm screwed anyway, cause there's NO WAY I can keep it at that % after I glue it anyway.

I have a second dehumidifier I can plug in temporarily to hopefully bring it a little lower just prior to glue up.

Dave

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Dee Tee

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Everything I've read says 40 to 50% so I'd say you're fine.

Kevin Looker

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I'm just a guy who builds guitars in his basement.
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You're good - I keep mine between 45 and 50.

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You are absolutely fine. What is a sump hole? It sounds creepy.

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OK, so say you lived in the Amazon where humidity is probably in the 80-90% ALL THE TIME. And you have a guitar there that was built at 50% RH, guess what would happen to it. It would swell a bunch and the top would rise and cause higher action.

My point really is, you want to build your guitar in the average RH that it will live it's life in. So, if your average RH outside of your shop is 60%, why wouldn't you build your guitar in that range?

If you live in the Desert where the RH is 30-40% on average, you'd want to build your guitar down at 30% RH so it remained stable in it's long term living environment.

40-50% RH is a basic guideline to follow, not a set in stone rule. It's all about where the guitar is going to live after it's finished that matters. That's what you want to think of when building. Professional builders never know where they're instruments are going to end up, so it's much better to err on the dry side of building 35-45% as most environments are more humid than this and a bit of swell is much easier to handle than shrinking wood.

All this to say I think you'll be fine, but I wanted to educate you as well.

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In Taiwan the RH is always around 80-90%, but I do all assembly in a dry room kept at around 40% because I am assuming that the guitar could travel to a drier climate, or even played in an indoor environment (such as a heated room) with lower humidity.

Going to a higher RH than its build environment isn't bad, the worst you would get is higher action and maybe (subjective) worse sound, but going to a lower RH than its build environment is worse, caved top, soundboard/back cracks, etc. is the likely result.

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Beautiful. That's kinda what I figured, I'd just perused quite a few threads here, and heard some pretty awful stories, and so wanted to make sure I was giving RH the respect it deserves. I'll keep the dehumidifier running and the RH at around 50%. If I shut it off, it goes up to 60 in about a day, and 70 in about 3, so I'll try to avoid that.


Thanks fellas!! I feel a lot better now.

btw, A Sump hole is a small hole in the floor of a basement about a foot and a half wide and 2-3 deep, with a sump pump in it to pump away rising ground water from under and around a house, also to pump away any basement spills or leaks. My pump runs a few seconds or so every day. Not overly creepy I'm afraid.

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Dee Tee

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"If something is worth doing, it's worth doing right."

Does your dehumidifier have a humidistat? I would avoid any dehumidifier without one because I've seen one with only a timer and that's it. The way I set up my dry room is I have the dehumidifier mounted on the wall (right now its just held up by a chair and a stack of bricks... I just need to get around to making a mount for it) and I would stick a drain hose in the machine and instead of filling up a bucket and having to empty that every few hours (believe me, in Taiwan you'd have to empty them every hour) the water would run out the hose which goes through a defunct window into the next room which isn't being used, and into a floor drain. That way I just dial in the humidity I want (I monitor this with a calibrated hydrometer) and leave it running in the background. So even though it's 90%+ outside, the dry room is always kept at 40-45% RH and I set my go-bar deck inside that room as well as storing any tonewood inside. I leave the wood to be braced inside for at least a day before I start bracing it.

I also use the room to keep any pieces I just sprayed with lacquer so that it would cure faster.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

My humidity fluctuates a lot,
and I don't have the option of a controled environment,
so, what I do is glue braces at 42% on the top and back,
glue the top and back on when rh is 42%.
Also, having a dome or an arc helps, so when it expands,
it has somewhere to go.
I learned the hard way building a couple of dead flat-tops
at high rh,
and whoa!

Something doesn’t sound right here. You reported that the RH for the rest of your house is between 60-70%, which seems way high, unless you are humidifying the air by some artificial means. Simply heating your house on a cold winter day will lower the RH significantly.

E.G., Weather for Cayuga, ON, Canada today:
34°F
Light Showers Snow
Wind: SW at 23 mph
Humidity: 93%

For example, the weather today in your area says it’s 34°F and 93% RH. Plugging these values into a standard psychrometric chart (or the following web applet) you can see that the RH inside your house would likely be much lower than your reported RH, hovering around 30% in this example, depending on certain variables.


Check out the applet here:

http://itg1.meteor.wisc.edu/wxwise/relhum/rh.html

It may be that your RH meter needs calibrating and if so, your shop RH may not be what you think it is.


Joe

I'm assuming this is in a basement and your floor is poured Concrete. If there is no vapor barrier between the Concrete and the soil (where the water is) the floor acts like a big wick and emits a constant stream of water vapor. If you can seal the concrete you will push the water into the outer foundation walls and then to the outside and lower your humidity. Laying down a heavy duty poly sheet on the floor and exposed soil in the space will help.

I think building a guitar for RH climate is a sound advice.

I had always thought that a guitar build at a lower RH going to a higher RH should not be a problem and the reverse: guitar build at higher RH going into a lower RH spells troubles (cracking top risk)
But recently I have seen a guitar build at lower RH going into higher RH environment having crack issues too.
It cracked right at the top's grain line where the bridge ends sit right on the grain line.
The only reason we can deduce is a too abrupt changes in RH causing the stress on the top.
(The owner discussed with the luthier and they think its likely the possible cause of it).

According to the owner, he does have a habit of switching on the air conditioner at nite, RH about 50% and the average surrounding (w/o aircon) RH is about 65%-85% in my country.
This could be the reason for the crack I supposed.
From what I believed, the guitar was built in a 45% RH environment in Germany.

Not sure if others have the similar experience?

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Sen CL Goh
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