Wood drying

[bluegrassplayer]

I'm thinking of making a mandolin from scratch next year so if I buy wood from a supplier do I have to let it sit and dry? I was wondering because I want to know when to order some.

Any help would be great,
Micah

[John Bertotti]

Depends on how wet the wood is you buy. I bought mine from spruce most was cut in the late 90's but one piece was cut the previous year. I have had all of it in my house for two years, now I'm using it. Probably you won't need to go to that length but like I said it all depends on how wet the wood is to start. I'm sure someone will post some drying tricks to speed things up if you need them. Planning on building next year, to me means buying the wood now and letting equilibrate to your environment. John

[bluegrassplayer]

Wow,
Mr. Hamlett sure is smart. I hope to be that smart someday.

[sunburst]

Sorry for the rambling, guess I got a little carried away.

To see if your wood still needs to dry, you can weigh it on a accurate scale, and if it's still loosing weight, it's still drying. If the weight is stable it's dry.

[oldwave maker]

If you're looking for engelmann spruce, don musser has some dry stuff near me, bitteted in the late 90's. we just had some nice rain around here jan 29 2005 so it should be drier than a roadkill alice springs kangaroo!

[John Bertotti]

Oh heck. I missed something. John I always learn something from your rambles keep it up you to Bill!

[PaulD]

Sorry for the rambling, guess I got a little carried away.

To see if your wood still needs to dry, you can weigh it on a accurate scale, and if it's still loosing weight, it's still drying. If the weight is stable it's dry.
I'm bummed I missed the ramble too... http://www.mandolincafe.net/iB_html/non-cgi/emoticons/sleepy.gif ya snooze, ya loose, right? http://www.mandolincafe.net/iB_html/non-cgi/emoticons/laugh.gif

pd

[rhetoric]

So do you leave the bark on when drying?

[thistle3585]

I was once told 6 months of drying time per inch of thickness. What I wasn't told was what the starting point is, but I'd think that if you bought a a top or back from a respectable dealer then a couple months, at most, of acclamation at your shop would work.
I've often wondered about people's drying techniques because it seems to be laden in a lot of myths. Can anyone honestly tell the difference between a piece of maple that has been drying for 1 year vs. 5 years? Is there a change in cell structure as a result of oxidation or such? Also, anyone want to define seasoned wood? Just curious, and I too enjoy your ramblings John.

Andrew

[violin2233]

As a Tonewood Supplier, Spruce that is cut into a wedge and then has a saw centered so that you can eventfully pull it apart before you join it will take about 2 years to air dry to be ready to use by a pro. Some makers like to have older spruce but if you do a moisture test you will see that it is less then 7%. Maple will take in moisture too. If your Spruce has been shipped through a humid area you may want to wait and let that spruce stabilize in your climate for a few weeks before use. Maple takes longer to dry. 3-4 years before use and again let it get used to your climate and etc.
You can tell the difference between 1 year wood and 5 year wood due to weight verses volume but even that can be tricky because density levels of wood vary. You develop a "feel" for wood and sink your nails into it and cut off a piece and smell it, feel it, break it and then cut into it.

[sunburst]

Wood dries faster than most people think. Bruce Hoadly says 4/4 (1 inch thick) Spruce will air dry from a green condition in 30-120 days, and 4/4 Maple in 50-200 days. Just leaving it in the shop for a while will work, but the amount of time needed cannot be predicted with accuracy unless you measure moisture in some way.
A good moisture meter will tell you when it's dry, but, as I posted before, weighing the wood every day or so on an accurate ballance or scale will tell you if it's dry, or at least at equilibrium with the air in your shop. If your relative humidity is properly controled, you can be assured of dry wood when the weight is stable, meaning the wood is no longer loosing weight.

Once the wood is dry, it will not stay dry if it is not kept in an environment of correct relative humidity. Wood is hygroscopic, and will take on moisture from air that is too humid. If that happens, it needs to be dried again.

There is some arguement about seasoning of wood. Some believe that wood that has been kept as lumber for some time changes in some way, and there probably are some chemical and physical changes, beyond drying, that go on as wood ages, but it doesn't continue to dry beyond equilibrium with it's environment, and the scientific evidence that I know of doesn't support the notion that wood becomes more stable with seasoning, or with repeated moisture cycling. It's possible that internal stresses in the wood could equalize to some extent over time, but 1 year old dry wood isn't measurably different from 5 year old dry wood, or 50 year old dry wood, unless there is degrade from poor storage.

If you read and understand Understanding Wood, by R. Bruce Hoadley, (the source of most of this drivel) you will be just as smart about drying wood as I am.

[Bill Halsey]

Perhaps. But it's a lot neater when a respected maker presents it...
Thanks, John.

[Dennis Russell]

Send your wood here to Yuma Arizona, so hot here and dry I seen two trees chasing a dog.. 110 yesterday only 12% humidity been that way for about a week. we had a chill the other day dropped to 103 I had to look for my overcoat and long jhons. Yes wood will dry out quickly here, only takes a few days for any woods to dry out, using a moisture meter for wood that lumber yards check thier stock all the time, bad news on hardwoods left out side for any length of time. Dennis In Yuma Arizona

[rlw]

" Send your wood here to Yuma Arizona, so hot here and dry I seen two trees chasing a dog. "

Now that is DRY with a capital D.

Let me interject a quick question here.

I had about a 6"x12"x6' slab of walnut out in my shed it's been there about 4 years now. I would love to throw it on the band and make some neck blanks and sides out of it.

Any ideals how long it will taken to dry out up here in Michigan. No problems with tree chasing dogs up here.

[sunburst]

A piece of wood that size, I would band saw into oversized rough blanks for necks, or whatever the intended use, and let it dry a while longer, if it isn't 8% moisture or less. If it's been in an unheated shed, it's probably still higher than that.
It could easilly have internal stress even if it's dry, and the smaller pieces might warp and move. If they are oversized, you can wait until they stabilize and then mill them further. It's not a bad idea to mill neck blanks in several stages so that they can equalize/stabilize/de-stress several times and stand a better chance of making stable necks.

[Michael Lewis]

6 X 12 billet should take 6 years or so so dry. It depends on the tree and the environment. I have had some walnut that took more than twice the suggested " 1 year per inch" and some other that dried in much less time. Always remove the bark, as this is where the bugs and bug eggs are hiding.

If you can wait a couple more years til the wood is dry to cut the 6 X 12 walnut you should have less waste than if you cut it green. Green wood can deform and warp a bit as it loses moisture, so as John H. suggested, you can cut it on the large side and trim the warping away after it dries. If the billet is not completely dry when you cut it open it can develop damage due to the uneven dispersion of moisture. The outside is dry and the inside is wet, then when you cut it some surface of each piece is dry and some is wet which will set up stress in the wood as the wet side quickly dries. To avoid such situations I prefer to mill the wet wood into 2 or 3 inch planks and sticker them to dry for about 5 years or more. Otherwise any large billets have to wait years til they are dry before further milling.

[Mario Proulx]

Nobody's mentioned "seasoned" yet, so I will.

There's a big difference between dry wood and seasoned wood. Wood can be dry to the point of being dimensionally stable in little time, as Hoadly suggests, and for most woodworking, that is all that counts.

But we aren't woodworkers, and our items are not simple, static objects.

I have cut up a couple handfuls of spruce logs into tonewood, most of it cut as guitar tops. Cut at roughly .200" slices, the green wood is "dry" and ready to work in a couple months. But it isn't ready to become an instrument yet. While techically dry and stable, this wood still has little stiffness, and has high damping properties, meaning it responds to a tap with a dull thud. Left stickered to further season a few years, this same wood stiffens up considerably, and begins to respond to a tap with a lively ring and clearly defined note.

Keep the above in mind

[Michael Lewis]

Mario is correct. It seems that engelmann is especially like this, and needs time to season. Get your wood as early as you can and let it age as long as you can. There is good reason the violin world loves old wood. Sure, you can use new wood, just like some factories, but you will get better results and have far fewer waranty repair headaches if you use older seasoned wood.

[sunburst]

Mario, Michael, or anyone, can you point me toward any papers, articles, or recorded measurements to support wood getting stiffer as it ages? I haven't seen any before.

[Michael Lewis]

John, I don't know of any papers or books, but I have had personal experience with engelmann getting stiffer after a few years. We aren't the only ones to experience this either, as other makers have mentioned this. I would be interested in the reason(s) if you find an explanation.

[violin2233]

What happens to wood when it gets wet? it can bend and become flexible. What happens to wood when it is dry? it gets stiffer. Wood can shrink up to 10% due to the water leaving/drying. A green piece of wood can weight almost twice as much as a dry piece due to water soaked into wood/cells. Once the water leaves the wood shrinks and becomes slighty denser causing it to be slightly stiffer. Dehydrate almost anything and what happens? It gets stiffer. So why CAN'T this happen to wood to some degree? Tree Rosin/sap does the same. When it is fresh it will be sticky and like syrup. Store it and dry it.. what happens?.. It gets tough or hard. Spruce is full of sap and why can't this help make the wood stiffer? Flexibility can be more noticable on softwoods and the effects that drying and seasoning have. If you have Guitar Tops cut up, lots of folks flex them to find the stiffer top. I have heard many folks talk about wood stiffening after it has seasoned.

[sunburst]

Wood does get stiffer as it dries, but a guitar top can be dry in a week. After that, it's in equilibrium with the air around it. It will take on and give off moisture as the relative humidity goes up and down.
A simple "deflection" test of the same batch of guitar tops when freshly cut, when dry, and when "seasoned" for various lengths of time would support whether or not the anecdotal evidence of spruce getting stiffer with age is measurable. I'm just wondering if anyone has done that.

I know Bob Taylor has done some tests with guitar woods, and claims to have found very little difference between new and old wood, but I don't know what specific tests he has done.

[violin2233]

But Sap does not dry in weeks. As the Sap dries or leaves couldn't the spruce get stiffer? Sap does harden when it dries and it does not take only weeks. I wouldn't dare sell any spruce guitar tops to a single maker with a drying time of a few weeks because it would be too unstable. Although i would LOVE to import tonewood that has a drying time like that because then I would be able to get an unlimited supply of ready to use wood. It is getting harder to import dry wood these days.

[sunburst]

Sap does dry in weeks or less in guitar-top thick spruce. As soon as it stops loosing weight (moisture), it's dry.
That's not to say that the sap doesn't harder after staying dry for a while. Perhaps it does, I'm not sure, and if it does, perhaps it does stiffen the wood.
I'd like to test some pieces for stiffness green, dry, then "seasoned", but I'd like to hear from anyone who has already done that, because I don't know if or when I'll be cutting any more spruce tops from the log.

[Chris Baird]

Both Taylor and Collings cook their spruce. The idea, I believe, is to rapidly accelerate the crystalization of the resins in the spruce. I'm not sure how long it takes for the resins to crystalize under normal circumstances but it happens much faster at 200 degrees. Or so I've read on the internet. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/wink.gif

[kww]

Elevating temperature to accelerate crystalization sounds bizarre. Higher temperatures tend to slow solidification, not accelerate it.

Higher temperatures do tend to improve the quality of crystalization. Freezing things very rapidly can interfere with the molecules ability to form the regular pattern involved in a crystal.

That said, someone has to show me a sap crystal before I think they exist, much less have anything to do with seasoning wood.

[Chris Baird]

I don't really know, I'm just spreading rumors. But, here is a link to a Disscusion (http://luthiersforum.3element.com/forum/forum_posts.asp?TID=1008). I've heard a number of terms used to describe what happens when one "cooks" spruce. I don't think crystalization is a proper term but it has been used.
I've not cooked any spruce but I have cooked resins down and they get harder and more brittle as a result.

[james the bass]

http://www.youtube.com/watch?v=-pKKRNDdV7M&feature=related
Nagyvary wet seasoned wood

[Fretbear]

I have had occasion to have to undertake building projects with wood that was green or greener than I would have liked. I once spacer-stacked all the local blue cedar (a pretty hard softwood) planks and 2X4s that I was using and let an oscillating fan play over the stacks 24 hours a day for two weeks non-stop. Everyday the place smelled strongly like someone had been milling green trees in there, and afterwards the wood was completely stable after the door and cabinet construction was finished. I estimate that the wood would have taken a good deal more than twice that long to season the same amount without the fans ventilating. This was softwood, but there was no cracking either.

[GTG]

I guess this is an old thread, but it is on something that I have some experience with, even though I'm not a builder and am a poor woodworker at best. I have done about 5 years of research on pine resin (not sap - sap is water-based, resin is terpene-based), and the resins of other conifers are fairly similar in chemical composition. The context for me was forest ecology - interactions between fire injury and bark beetle attacks, but the papers I've read on resin chemistry were general in nature.

Resin is a mixture of resin acids (rosin) dissolved in monoterpenes (turpentine). Turpentine, just like the commercially available chemical, is volatile, and evaporates when exposed to air, leaving solidified rosin behind. Resin can remain liquid (ie still contain turpentine) for some time (years, likely dependent on species) after tree death or cutting. So it makes good sense that cooking, or perhaps letting wood season for several years, would decrease the turpentine content of the resin and produce a more solid assemblage of wood and rosin. The resin canals and ducts are separate from the xylem tracheids, so water would naturally escape much more easily than turpentine when exposed to air.

I don't know if this is the reason that people say boards feel stiffer or sound better after years of seasoning, regardless of moisture content, but it does make some sense from the resin chemistry perspective.

Because of the differences between resin structures in wood of different species, if this is the correct mechanism, it should be an issue with pines, spruces, larch, and douglas-fir; not so much with cedar, true firs, and other conifers. I don't know about hardwoods, but I would suspect it's quite different.

[sunburst]

What do "terpentine" molecules look like, in other words, how big are they and how volatile? Do common turpentines evaporate faster or slower than water, and is there any covalent bonding? Surely nothing like the hydrogen bonding in water(?). Why do the resins still contain turpentine after years of storage?
What I'm getting at here is this; it just seems to me that turpentine would evaporate out of the wood faster than water unless the molecules are considerably bigger.
I know that the heat of kiln drying will "set the resins" in pine and spruce, and that sounds like a logical explanation, heat driving most of the remaining turpentine out.

[GTG]

Turpentine is the common term for a mixture of (mostly) monoterpenes - C10H16 molecules. Yes, definitely, monoterpenes are much more volatile than water, but are not distributed evenly throughout the wood, and not nearly as 'diffusable'. Water moves through conifer wood through the elongated tracheid cells, diffusing very freely through the pits (openings across the surface of the tracheids). It's a very efficient system for moving water, allowing the tension created by transpiration at the leaves to raise water quickly and readily from the roots throughout an entire tree. In contrast, resin is produced and stored (in pines, spruces, larches, and douglas-fir) in resin canals - a sort of plumbing system throughout the wood composed of parenchyma (living cells); most of the functional tracheids are dead, essentially just acting as piping. There is no diffusion from the resin canals to the tracheids, and therefore the resin is only exposed to air when and where the canals are severed. Low viscosity (especially when cold) ensures that it flows slowly, and I'm suggesting (but don't know for sure) that all this contributes to much greater persistence in dead wood.

Picture how quickly a sponge dries out in the air compared, say, to a piece of very thin rubber tubing - because there's so much less air exposure, the tubing will still contain moisture long after the sponge is dry. Now think of a piece of tubing of microscopic diameter - only a few cells, and microns wide, and a much more viscous liquid. This is the kind of structure we're dealing with.

Like I said, I don't know anything about how this affects tone or the stiffness of a piece of wood. Seasoning may well cause other changes in wood structure (or maybe not). But it does seem plausible that driving out the liquid fraction of the resin would take much longer than driving out the water, and heating would help volatize the monoterpenes, increase the pressure and decrease the viscosity of the resin, speeding up the whole process.

[GTG]

Actually, having written all that, it's not the same for douglas-fir. IIRC, D-F has a slightly different resin system, with resin 'pockets' rather than canals. I suspect the effect in terms of seasoning (if this idea that it's affected by resin is correct) is similar to the other species mentioned.

[Graham McDonald]

The idea of cooking guitar soundboards at around 180-200F has been around for a few years. As someone mentioned Taylor and other do it routinely. I have been doing it regularly with flat soundboards, but have not had the courage to try with a mandolin carved top blank. The last couple of guitar tops I used were weighed before and after cooking in a standard domestic electric fan forced oven at around 180F for an hour. An englemann top lost 5-6% and a lutz spruce top 6-7% in weight and both seemed a little more 'zingy' in the tap tone. What I didn't do is weigh them again a week or so later when they would have re-equalized to the workshop environment. Both tops had been cut and dried for several years and it doesn't take long in our summers (not quite as radical as AZ or NM) to get to an equilibrium moisture point, so that extra 5-6% loss from the oven had to come from somewhere and the feel of the wood is different after cooking. An area where there is lots of speculation but little actual scientific data

cheers

graham

[sunburst]

Well, C10H16 is a bit bigger molecule than H2O.
We seal the end grain of wood for drying (normally) so the water molecules must diffuse through the cells and make their way to the outside or the wood more or less laterally. It is the bound water, not free water, that is leaving the wood as it dries beyond fiber saturation point, it isn't localized in any particular structure, is it? Is the C10H16 too big for that, or at least too big to do it as fast as water, or are the resin canals more impervious to the monoterpenes than the cell structure is to water?

Maybe I should just ask if you know where I can read up on this so I'll stop asking so many questions! :)

[Schlegel]

Well, I know that water can evaporate out of an oak barrel of Scotch or Brandy, leaving the remainder lower in volume and higher in alcohol content. The effect is so pronounced that the barrels develop a partial vacuum and you can hear the air rush in when you remove the bung. The increase in alcohol content has been measured countless times by those in the industry. My point for all that is that alcohol is smaller than turpenes, etc., so if alcohol can be trapped but water still evaporates out, the same must be true of other volatiles. I'll bet, though, that they weigh a lot less than the water left even in dry wood.

[sunburst]

The barrel story points to molecular size alright, since alcohol is more volatile than water (ignoring the whole azeotrope thing). Easy enough to assume the oak is filtering the larger ethanol molecules so more water makes it to the surface of the barrel to evaporate. Seems reasonable to assume something similar with the monoterpenes. Hmmm...

[GTG]

Well, John, those are great questions! I certainly can't answer all of them, but I've attached a technical review article which briefly talks about resin production and bark beetles to show that I'm not making this stuff up! The real questions you're probably interested are in, the wood properties stuff, are more the domain of wood anatomy rather than forest ecophysiology, so maybe there are others with more specific experience who can chime in (although maybe not - we're getting pretty specialized here).

Here's what I understand (or think I do) about resin canals in pines and spruces. The canals are made up of epithelial parenchyma cells that form a tube-like structure. The epithelial cells are located amongst xylem tracheids in vertical and radial orientations, and are interconnected so as to form a type of plumbing that can extend for several meters (in pines; not sure how long in spruces). Surrounding the epithelial cells are another layer of dead parenchyman cells that become filled with air. These sheath cells support the epithelial cells and shield them from the tracheids. The epithelial cells, via various biochemical pathways, produce resin in their leucoplasts and exude them into the intercellular space between cells, forming the 'void' of the canal. The resin is stored under considerable pressure (during my experiments, we measured over 200 psi in some living trees), and it's important that it remains shielded from the tracheids, because those are under extreme tension from the water being drawn by the action of evapo-transpiration at the leaves. So this is why I am saying that the resin transport system is quite separate from the water transport system, and therefore more impervious to diffusion through the cell walls, at least in living trees. If it were not, the resin canals would quickly collapse from the sap tension in the tracheids surrounding them.

As I mentioned before, water transport in tracheids flows very freely in vertical, radial and tangential directions, while resin only flows through the canals, and therefore only in very strict locations in the wood. There are far more vertical than radial resin canals in the pine species I've read about, but I don't know specifically if that's the case for sitka (or any other) spruce. Resin plays a role that is to some extent, like blood for us: it flushes wounds, and then scabs over (monoterpenes evaporate, leaving rosin) to protect a wound from fungi or other pathogens.

Now, all this is in living trees. In dead trees, or pieces of dead trees, things are probably different to some extent, although all of these structures I'm talking about contain cellulose, lignin, and other complex carbohydrate molecules that give them stiffness and make them hard for insects and bacteria to break down. Tracheids, for one, are already dead in living trees, so they probably don't change much. The high pressure in the resin canals is inevitably reduced as resin is squeezed out from wounds; this is why, when a spruce is cut down, the stump (and the wood, sometimes) exudes resin. It doesn't take much resin loss to reduce the pressure to ambient levels. I've definitely seen dimensional spruce lumber with still-wet gobs of resin in some places, but no, I haven't seen any studies done on the loss rate of monoterpenes in dead wood samples over time.

I do know that ponderosa pine resin in open test tubes begins to crystallize very quickly, especially if it's warm out, but can remain somewhat liquid for months. I had a couple of open samples sitting around in my lab at the U of Washington (they smelled nice) that were still goopy and viscous in late fall after being collected in the summer.

There you have it. I don't know if any of this actually is relevant to the 'wood seasoning' you luthiers are interested in, but it might be.

[sunburst]

That's quite a bit more than I knew about conifer anatomy, though I was a Biology major in college well back into the past century so some of the terms have a vague familiarity. :) Thanks for the overview!

[GTG]

Yeah, I kind of got carried away there. "What, someone's actually interested in resin??". Heh, good fun.

[sunburst]

If I understood even less of all this it still makes me realize that there is something going on with resins in spruce after drying. Whether or not that has much to do with building a mandolin is another subject. So much to learn...

[tree]

. . . So much to learn...

Isn't it a grand journey, though? I started to jump in when I saw parenchyma and tracheids and cellulose and lignin being tossed around, but I'm glad I kept my mouth shut - I would've been in over my head, and I'm a registered forester and a certified arborist. I'm really impressed with John's interest and tenacity in understanding this stuff, which (on the surface, anyway) seems to be outside of the luthiery realm. I think there are probably lots of connections between tree biology and instrument building that can help builders push the envelope of understanding why some things work and some don't.

[Dave Cohen]

A word of caution about the monoterpenes. There's terpenes, and then there's terpenes. They share an isoprene structure, but within that limit can still be very different. Some, like menthol and eucalyptus oil, have substituted 6-membered rings, while others are non-cyclic. Some are plain ol' hydrocarbons, and some have a hydroxyl group or an aldehyde group or a keto group. What's the significance of all that? the oxygen containing terpenes will be somewhat more polar than the plain ol' hydrocarbons, and will undergo some hydrogen bonding to water and/or to hydroxyl groups or to the ether linkages on cellulose and hemicellulose. That means that they will be "stickier", i.e., the attractive forces between molecules will be stronger. The idea was tossed around in some posts that the terpenes wold be much more volatile than water. For the plain ol' hydrocarbon terpenes, probably yes, since they only have Van der Waals forces to overcome. But for those monoterpenes containing oxygen, maybe not too much more volatile than water. The "volatility" is related to more than one physical property. It decreases with increasing molecular weight (the terpenes are higher MW than water), but also increases with the enthalpy of vaporization. The enthalpy of vaporization is related to the types of intermolecular forces. The hydrogen bonding and polar interactions in the oxygen containing terpenes are much stronger than the Van der Waals interactions in the plain ol' hydrocarbons. Hence the enthalpies of vaporization for the oxygen containing compounds will be higher, and so those might not be much more volatile at all.

Remember that water is the abnormal one. Despite a MW of only 18, it has an abnormally high boiling point of 100 deg C, principally due to hydrogen bonding. In that perspective, the monoterpenes (even the plain ol' hydrocarbons) are not really so highly volatile.

http://www.Cohenmando.com