understanding moisture content

[thistle3585]

Okay, as I venture more into instrument building, I'm trying to understand the drying issue and how it translates to building. As a woodworker, I normally buy material kiln dried between 6-8% MC. My questions are 1)What is a preferred moisture content at time of construction, 2)what is a preferred method of drying? Is there a process I should be cautious of? I have gotten the imprerssion that kiln dried material may be too brittle.

[sunburst]

6-8% is good. It doesnt matter, structurally, how it gets there. There is no evidenced that I know of of a difference in strength or stiffness between air dried and kiln dried wood as long as it is dried correctly.

Some woods, like walnut, keep a more natural color when air dried because it is not steamed as in kiln drying.

Spruce can have more little spots of sap showing up on the surface if it's air dried. The heat of the kiln seems to bake the sap into place in the wood so that it stays put.

[Spruce]

" I have gotten the imprerssion that kiln dried material may be too brittle. "

Improperly kiln dried wood tends to be brittle...
If the kiln schedule is adhered to correctly, wood with a nice workable texture is the result...

"6-8% is good. It doesnt matter, structurally, how it gets there."

If you rush the drying process, brittle wood will result...
Texture in wood (especially maple and the hardwoods) is determined by how quickly the wood is dried...

[labraid]

Resins and oils evaporate to varying degrees at kiln drying temperatures which can, for certain woods, be rather low (110F starting, oak) or rather high (230F starting, pine). Pollution from kiln drying wood (VOCs) is a problem for the environment, which I say just to show that this evaporation really does happen. These oils help keep the wood supple and pliable. Being a bowyer, I have read (and because of stubbornness, found out through experience) that kiln dried woods crack (shatter!) easier than air dried wood in wooden bows. Sooooooooooo, as for wood in musical instruments... oils and resins make up part of the wonderful spruce, walnut, maple, and ebony, among others, that we love to use. Taking out some of these oils (evaporating some of them or a lot of them) changes the properties, both strength and therefore tonally as well. But just to prove another point, go and smell your favorite air-dried spruce specimen. Smells good eh? That's resin evaporating this very minute, at room temperatures even. So you can't escape it, though you can minimize it (get air-dried). If yer gonna make an instrument and you want it to be the best possible, get the best possible, it's worth the effort in tracking down the good stuff. And air-dried wood doesn't cost that much more. You'll sleep better at night (and enjoy your playing better in the day!)

[Big Joe]

We have specially designed vacuum kilns that our wood is processed through. It evenly removes the moisture so the moisture content is the same throughout that piece of wood allowing it to become very stable. We use this process on all our woods whether kiln or air dried. Until they reach a stabilization point it is not used in any or our instruments whether guitar, mandolin, banjo, or dobro. I do not know much about the process but I have gone through the wood plant and viewed the process. It was quite interesting. The woods we use are very stable and that helps with making instruments that are very consistent.

[cutbait2]

in my part of the country air drying is insufficient to remove enough moisture to leave the wood stable enough for cabinet (or instrument making) my understanding is that the additional energy (heat) provided by the kiln is necessary to remove cellular moisture. once the cellular moisture is removed (in accordance with the proper schedule) then the wood may regain some extracellular moisture in storage but this is easily removed. it may be a regional bias but i would not use anything that was simply air dryed in cabinet or instrument making, ( and contrary to others nor would i (or most of the local cabinet makers i know) use anything that moved when i cut it or moved as it laid it my shop, but that's just me ). i'm in north Florida.

[labraid]

Joe, yer right, I should've mentioned vacuum kilning... A low temperature process which is very good for retaining the natural oils in the wood. (water boils under sufficient vacuum at room temperature, while oil will tend to much less cause it's a bigger, heavier molecule) This is a superior method even to air-drying because there is all control over the drying process and it occurs at lower temps. Last time I heard (long time ago) this method was being developed (Sweden?) but was too expensive at the time for normal large scale use (construction). Instrument building woods are every bit worth the expense though. It'd pretty hard to find the guy down the street with a vacuum kiln for his personal luthierie setup though.
Cutbait, you're right it's a regional thing and obviously too humid for it there. I wouldn't be surprised if mold were to start growing on an attempted air-drying pile in just the first few days in Florida. Not good. However, when done properly, air dried wood does not move any more than properly kiln dried wood. Ends must be waxed. The water in the cells should evaporate slowly enough that there is no skew in the balance from the outside to the inside, as far as moisture content goes. A skew such as this, as you know but I mention it for interested others, is what causes internal stress and movement upon cutting. This can be accomplished through fans and louvers in the ceiling to regulate air circulation and humidity in the room.

[John Bertotti]

Is it then inappropriate to dry you wood in a room with good circulation and a dehumidifier? I figured it would take longer but the changes could in moisture could be brought about much slower. I don't know if that is good or bad but have used and the wood seems stable. I haven't used the wood in an instrument yet. John

[Luthier]

If the wood is seasoned properly, and if you build in a controlled environment and make it a practice to use a hygrometer to measure the humidity, you should be fine. #Again. The main problem will occur if the finished instrument is subjected to extreme heat, cold, or a vastly different change in climate. #The wood can take on moisture better than it can release it.

Don

[Spruce]

Around here the primary reason for the use of kilns is the prevention of fungus in the maples and spruces (sans Sitka), and not as a tool to get the wood to 6-8% MC...

I shoot for 20% MC and then AD it from there...

[John Bertotti]

I have been able to take my wood down to about 22% with the dehumidified room. Then I let the wood sit for a couple years in the environment I'm working in. I guess it may never get to 5-6 % which I think is bad if the instrument will be moved to drier climates. I will have to reevaluate the final drying steps apparently. Thanks John

[Spruce]

" I will have to reevaluate the final drying steps apparently. "

I've posted this several times, but it's a cool way to get that "final cure" on wood you're getting ready to use...

An excellent way to artificially season wood is to use a black garbage bag.
This is especially useful for larger pieces of wood...say, a cello neck...
Put the wood inside of the bag and stick it in the sun. #Important! Seal the bag...
Let it sit for a few hours, then turn it inside out to evacuate the moisture. #The small volume of the bag will insure that the wood will not dry too quickly and crack, or case harden...

This method is great for a "final cure" on pieces of wood that you're not sure of how much moisture is still in them...

[cutbait2]

all my reading indicates wood should be dried to 5-6% for cabinet making, my reading also indicates some form of added heat is neccessary to remove cellular moisture to this level of dryness. therefore my experience does not include using air dried wood for building things that might go into conditioned spaces. until recently we were fortunate to have a custom kiln operator in town where i had dried many a bd ft of red oak, heart pine, cherry, hickory, pecan etc that we use down here for cabinet work, trim, flooring etc. part of the drying process is carefully following the appropriate schedule, the other part is measuring the final moisture content. to me building with wood air dryed to 12-15-20% moisture is not worth the risk, nor is uncontrolled drying. finding a good commercial kiln that will run a custom schedule may be difficult but there are a number of plans available for solar kilns, small electric kilns. the only alternative for me is to purchased kiln dried wood. perhaps spruce has properties that make air drying in the right climate practical, i do not know.