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Hi all,

I've been reading about humidity in archives of this forum. My situation is a basement shop with out humidity control in Vancouver, BC (actually Maple Ridge), Canada. The humidity is shooting up right now, approx. 65%, but this is a short term rise.

I found this searching the forum, (From Post subject: go bar decks are so great Posted: 10 Feb 2009 01:55)



If this is a short term humidity spike is it safe to build in this temporary high humidity? I'm assuming the moisture level of the wood is not going to change appreciably over the next few days.

Also are any of you in the Pacific North West, and are not working in a humidity controlled shop? If so have you encountered any humidity issues in your building?

I'd like to get started on doing some neck laminations (maple/bubinga) and gluing ebony, rosewood, and ziricote fingerboards on. But will wait if doing so now is a set up for disaster.

Thanks for any advice,

Stefan Schmitt

An article on the subject in one of the last Catgut Journals indicated that wood can absorb or lose moisture fairly quickly: a matter of hours, iirc. It might take it a while to reach equilibrium, especially for larger, thicker pieces. We're working with thin stock, and the changes should be fairly fast.

My experinece is that basement shops are pretty much a lost cause unless the building was carefully made to exclude water vapor from the beginning. Concrete is more or less 'transparent' to water vapor, and waterproofing coatings are best applied to the outside, since it has low tensile strength. Some makers who are forced to work in basement shops find it worthwile to build a 'tent'; a light wood enclosure that is enveloped in plastic sheet. This can be dehumidified successfully. It only needs to be large enough to enclose your main bench and go-bar deck: you can go 'outside' to make a few cuts on the saw or drill press wihout running into too much trouble.

I have such a basement shop, and only perform the critical joinery aspects of building when I am sure that the humidity is in an acceptable range. Needless to say, since I live in the humid Midwest, I don't assemble the box in the summertime or glue braces on anything for example. I can do a lot of the other work without fear, and wait for cooler weather, when the heat comes on to do assembly. I do have a dehumidifier which runs a lot in the summer, but I wonder if I am only making the humidity swings greater and more frequent that way.

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"Building guitars looks hard, but it's actually much harder than it looks." Tom Buck

Stefan,

I live in Terrace on the North Coast of BC. The humidity ranges from 30% in winter to 65% or so in summer. I have a guitar under construction on my bench (been a couple of years now ) that moves quite a bit when I don't turn on the humidity controlling appliances. So much so that when I took this acoustic to a talk I did earlier this spring (it was very dry then) I noticed that the back had pulled away from the linings in the area of the cutaway (the guitar has a venetian cutaway). The back was noticably "off" from the sides. By the time I got around to fixing it the humidity was back to about 45% and I hard time locating the issue as the crack had closed up. So it was acutally the fluctuation in the moisture in the braces that is adding to the stress on the back (I have the binding channels cut but the bindings aren't installed so the area is weak at the moment).

Anyway, the short version, yes you need to be concerned about RH and no you should not build in high humidity. Go to Canadian Tire or better yet Value Village and get some appliances. I actually bought a humidifier for $12 at a Value Village, used but working great!

Shane

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Canada

The Pacific Northwest is a pretty friendly place to build. I live in Bellingham, WA and I don't have to dehumidify very often in the summer. But it's been unusual lately. You do need to keep track and dehumidify sometimes and, in spite of the our reputation for wet winters, I have to humidify when we get a cold snap.

As for how fast plates move with humidity changes, try putting a top on your bench with a 100 watt light about 12" above it. You can watch it move in minutes.

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http://www.chassonguitars.com

Stefan: I also work in a basement shop under some awful RH conditions. Started building in the mid 70's and quickly learned that the RH was boss.Here I start to get wood parts ready in Sept. and never get to gluing any braces till into Dec.Sometimes not till Jan. depending on how cold the weather gets.Winter and spring are ok here but summer and fall are out.Thin plates can pick up and lose enough moisture to cause problems in an amazingly short time.Building dry is far less risky then building wet.If you want to build under higher RH conditions you should have some means of control as the other fellows have suggested.

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A person who has never made a mistake has never made anything!!!

I have a basement shop in New Hampshire and I can't build for most of the summer. I have burned out three dehumidifiers trying to keep up. My sump pump has been running regularly this summer and I still get a wet floor.

Because of this problem, I have developed a sense for what you can and can't do when the humidity is high.

Can do:

• make heel and tail blocks.
• Thin and bend the sides.
• profile sides.
• Glue sides to heel and tail blocks
• Glue in linings.
• Thin, bookmatch and glue top and back
• Scarf and glue up neck.
• If the top and back are already glued on, you can cut binding channels and glue in binding and purfling.

Can't do:

• Glue braces to top or back.
• Attach top or back to sides.
• Glue in tail wedge.
• Attach fretboard to neck. Many ebonies have much larger expansion coefficients and you will feel a ridge when things dry out.
• Attach head plate (actually you might be able to do this when the humidity is high but it depends on the difference in expansion between the plate and the neck wood.
• Install the frets. If you do this when it is humid, you will get awful fret ends sticking out when it is dry.
• Any finishing work.

Mike: that is an excellent list (which mirrors my own intuition about these things). Thanks!!

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"Building guitars looks hard, but it's actually much harder than it looks." Tom Buck

I won't glue stuff together over 45%. I'm not working in a basement, but ocassionally the humidity gets high in my shop. I've got a small de humidifier, but it doesn't do much. To de humidify I have a small (1500 watt) space heater. I run it, along with my AC and it brings the RH down quickly.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Hi Stefan,

I'm going to dissagree with most of the posts. I'm just down in Stanwood, WA and right now th RH in my shop is 59-62% where it's been for a few weeks now (summer). I have no problems glueing up, never had, never will. In the winter I do work to keep the RH up between 45 and 55%. Honestly, has anyone ever had one of their guitars bust apart, crack, shrink or swell because they might have been glued up when the RH was at 60%? Now if your shop is in a basement and you know your RH conditions are way out of optimum, then you don't build or your get appliances that can change RH. Just my .02, but I think to many builders in our league go overboard with this.

Dave

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God, Family, Carreer

Dave,
I think most are just saying to build in the dry rather in the wet. Like I said, mine did come apart because the braces did move with humidity. I would hazard an opinion that that may not have happened if the bindings were on the guitar, adding much more strength in that area, but still it did give me the lesson about much and how quickly this can happen with humidity changes. I have been watching this particular box move quite alot over the past 3 years or so with humidity changes and am always impressed at the amount of movement that does actually occur on a well aged box that was made from well seasoned woods. But like everything else, you can take your chances and everything may be OK.

Shane

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Canada

To me its clear that wood, especially in thin plate form, expands or shrinks like crazy when subjected to a change of RH. Take a spruce top from your cool 45% shop out in the sun at 30% and it will noticeably bend within minutes. FLip it and it gets straight and so on. I don't think it takes long until you can get very measurable width differences.

In the end you can make the guitar at 70% if you want, but I think all parts should be glued near that point, and it should be well protected from low humidity. I personally do not glue anything outside 40-50%, and when it comes to bracing or important assembly, only if the ~45% was kept reasonably constant for at least a couple days.

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Build log

I work in a basement shop in Van BC, and it is certainly not a lost cause. I have a 10x12 enclosed work area with lots of air gap around the door. Still,a very small dehumidifier keeps everything rocksteady at 42% all summer, and a very small humidifier for winter does the same. I bought one at a garage sale for 30$ and the other at London Drugs for 40$. Even running loosy goosy things stay steady. Heck, in BC (grow show capital of the world) it can't be too hard to find a used dehumiditier on the cheap! Ha ha! But I wouldn't do any bracing or body assembly unless the RH is right, it's a sure-fire recipe for future angst. You can literally see pieces change sometimes in minutes, so why risk it?

Building at high Humidity is a good way to ensure that tops and backs WILL split if the guitar ever sees a really low humidity situation. Also leads to sinking tops, and backs losing their radius if they end up in a slightly drier environment than they are built.

The critical operation is Glueing on top and back braces. Because the braces shrink much less along their length than the plates do across their width. So the plates shrink, the braces try to restrain thar shrinkage-- crack.

BUT the critical factor is the wood humidity rather than the environmental RH.
I have glued top and back braces in an garage when it is raining, by heating the plates with a blow heater for a few minutes to dry them before bracing. (and again if the process is not finished in one stage)

I'll decloak myself for this one...

My basement shop is just shy of 400 square feet and it was purpose built last fall for guitar building. I had bought a basement with a house on top so that I could build this shop...

My shop has framed in walls, except for one 16' expanse of concrete foundation that I just painted. The house is built in blow sand and the drainage is phenomenal with the sump pump never once turning on in the over one year that I have lived here.

The walls are 2 X 4's, drywalled on both sides and even though the other half of the basement is heated I still used R-13 in all of my perimeter walls. I also stapled a vapor barrier all around the perimeter.

The floor of the main shop and saw room is exposed concrete and the wood storage and break room/office is carpeted.

Last winter with a medium sized humidifier I was able to easily maintain 43-47% humidity at all times. This summer with a small dehumidifier never running at a setting above 3 I am able to maintain the same range at all times. My shop is the most comfortable room in the house - as it should be...

I should note that the stinkin house that I had to buy along with my basement is also humidified in the winter which is necessary here in beautiful Michigan.

Maintaining a stable RH in an acceptable range for wooden instrument building is a must IMHO. On this forum alone I can't begin to tell you how many posts we have seen through the years where something untoward (I love the word untoward so forgive me please for using it) had happened to a builders guitar because they ignored the RH...

A couple of years ago I decided to do the 220 grit sanding on the bracing of a top that I had just completed outside. It was a very nice summer day and the RH was only 55% (I checked it with a calibrated hygrometer). To my horror in less than 20 minutes my 25' radiused top began to flatten right before my eyes. Returning it to the 45% RH shop and weighting it in the 25' radius dish reversed this. Anyway it was a lesson learned for me that RH DOES matter.

Mike's list is great and an excellent guide for builders who may be RH challenged for now. It's worth noting too and we have talked about this in the past but what did Luthiers do 100 years ago pre GE dehumidifier days? They did exactly what Mike has indicated on his list. They knew that depending on their specific climates certain times of the year provided opportunities to perform certain tasks and this probably led to some batch processing.

Lastly hygrometers are important and most of them are crap... There is a lot in the archives about this but it's worth mentioning to me since the question is how do you really, really, really know if your hygrometer is even accurate? Learn to do a wet bulb test and/or get an Abbeon and send it to California to have it calibrated at least twice a year.

I control humidity with home-made plastic bags, and large dessicant bags. Take it out to work, put it back, and let acclimate at least a week before gluing. Its a pain, but I keep everything within 8% range.

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Here is what a Parlor Guitar is for!
http://www.youtube.com/watch?v=oEa8PkjO6_I

Dave E asked:
"Honestly, has anyone ever had one of their guitars bust apart, crack, shrink or swell because they might have been glued up when the RH was at 60%? "

YES!

I'm in New England, which is Guitar Hell. I know one Texas maker who simply refuses to send guitars to New England any more. The R.H. right now is close enough to 95% outside that it doesn't matter, and in the winter it can go below 20%. Usually moving a guitar to higher humidity than the building conditions doesn't matter, but it can. I built a guitar one cold January that went down to the Ashville area, and promptly picked up enough moisture from the air that it became unplayable, and stayed that way for a while. The more usual thing is to see cracks in mid-winter as the tops shrink. After you've repaired a few of those in customer's guitars you get the idea that a dehumidifier is your friend.

Of course, if you're not shipping guitars to other parts of the country, and you know that the humidity in your area tends to be stable, it might not be a worry for you. We don't have that luxury here.

Does anyone know how Martin controlled humidity in the summer back in the day?

No, but i do know that almost any old martin (or any old guitar) that has lived a productive life outside of a climate controlled closet will have a multitude of repaired cracks!

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Jordan Aceto
Ithaca, NY

I would have to agree with how quickly thin guitar woods can absorb moisture, last night I took a bubinga set upstairs to show my dad, the windows were open in the kitchen and it was hot, within 5 minutes the sides were warped and buckled.

There's a great line in Understanding Wood:



Above all else relative humidity must be respected. If you do not respect it now, you will be forced to respect it later.

I had a top crack during a build when the RH dropped - fortunately it was under where the fretboard went. The humidity gets very low in the cold winters here in N. Illinois.

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"Building guitars looks hard, but it's actually much harder than it looks." Tom Buck

Hi All,

Shane, I'll concede after reading some more posts. Guess we in the NW are blessed after reading about NE! Was thinking about getting a de-humidifier for the summer months though.

Dave

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God, Family, Carreer

im worried about permanent high humidity

I live close to Galveston,, TX, super high humidity all summer, I make sure all joints to be glued are tight and clamped well and thats it. When others see my guitars they pick them up and play them. Look 'em over sort of good and play more. I have not noticed that the humidity has bothered them yet but I've only been building ten years now.
Still plenty to learn!