Is air dried wood really better than kiln dried?

[Frederick Skelly]

Hi folks,
I'm reading "A Cabinetmaker's Notebook", by James Krenov. He advocates using air-dried wood. He feels that kiln drying wood "changes and dulls the color of the wood, and the fibers are affected so that wood which has been kiln-dried feels different to me. It's got a different ring, a different texture; it isn't clear and fine." He goes on to say "Besides, kiln-dried wood is brittle." (Page 12)

I guess I can think my way through to that, though I've never actually experienced it. I don't mean to question a guru like Mr. Krenov. I just wondered if any of you have a similar view, based on your experience? (Seemed like an interesting thing to 'talk' about, on a long winter night, anyway!)

Fred

[Mike Henderson]

I've used both and didn't see a lot of difference. Maybe it was just the type of wood I was working with, or maybe I'm just not as sensitive to wood as Mr. Krenov.

Mike

[Charles Wiggins]

Previous threads on the topic:
http://www.sawmillcreek.org/showthread.php?9931-Air-Dried-vs-Kiln-Dried&p=77116

http://www.sawmillcreek.org/showthread.php?37370-Kiln-Dried-vs-Air-Dried

I would add that everything I read on steam-bending said not to use kiln dried wood, but I don't recall the reasoning right off the top of my head.

[Justin Ludwig]

Only air dried wood I've ever used is bois d'arc to hand make some bows and staffs. Its not fair to compare it to anything I use in cabinetry. Even hickory doesn't hold a candle to bois d'arc's "meanness. I still have a quarter of a 14" trunk that's 72" long I fell in Oct '05.

[Mel Fulks]

Mike and Charles are doing pretty well here. Guru is IMO good description of Krenov. Saying kiln dried is brittle is like
saying home made cakes are over baked. SOME of them are. Kiln dried wood moves less than air dried.

[Frederick Skelly]

Previous threads on the topic:
http://www.sawmillcreek.org/showthread.php?9931-Air-Dried-vs-Kiln-Dried&p=77116

http://www.sawmillcreek.org/showthread.php?37370-Kiln-Dried-vs-Air-Dried
.

Good catch Charles. Thanks for the links. I never thought to check the archives. Was just sittin here reading Krenov and had the question come to mind.:(

[Robert LaPlaca]

I bought 300 bf of air dried Walnut, it had a color and ease of workability that I never experienced with other purchases of Kiln dried Walnut.. Not so sure the experience with the air dried Walnut would make me only want to buy air dried lumber, but I now know that I wouldn't shy away from air dried lumber..

[Kevin Jenness]

It depends. Kiln dried wood subjected to an overly aggressive schedule can be full of all kinds of defects including surface checking, honeycomb, "brittleness", etc. Air dried wood is typically subjected to less moisture gradient and potential drying stress, but can be more prone to mold or sticker stain. You can screw up drying wood quite well with either process without any great difficulty.

I would take exception to the assertion that kiln dried wood "moves less" than air dried . Wood dried to a given moisture content will exhibit the same movement in service no matter how you get it there. Kiln drying does not change the hygroscopic quality of lumber.

[Peter Quinn]

I haven't worked enough air dried wood to offer a board based or deeply founded opinion. But from the little I have I can sense that Mr. Krenov may have had a point though he was perhaps verging on the dramatic. I made a set of cabinet doors from air dried butternut I was given to do the job, I've worked KD butternut, this wood was IMO more stable than most of the KD butternut Ive worked, and it had a "glow" or shimmer that the KD varieties seem to lack. Thats in the raw...once the finish is applied, really hard to say there was much difference. Ive also worked air dried walnut, and there the color was considerably better raw than the KD variety. Part of that may be most commercially available black walnut is steamed prior to drying to "equalize" the color....which I translate into the sayers attempt to pull a ruse an make the sap look like the heart wood in the rough, because the first shot through the planer and all the color variation comes right back out, but its all a little bit grey and flat. I have never heard an explanation of the steaming of black walnut that actually makes sense to me. The air dried stuff was very stable, much easier to read sap, and perhaps just a bit friendly on hand tools? Brighter color too, even after finishing. But the KD stuff is decent. I'm not a wood snob, I'll work pretty much anything thats dry however its dried, my being able to afford it is of primary concern.

[Mel Fulks]

I've got ANOTHER cake analogy ...air dried is batter ,baked is cake. There are plenty of sources that explain the difference
and those differences are the reason that the most widely used architectural specs always say must be "kiln dried".

[Prashun Patel]

the ir dried wood i have used has been in general easier to work than kiln dried.

[Sean Hughto]

There are exceptions to every generalization, but generally, given the choice, I would rather work air dried.

[Kevin Jenness]

The reason that kd lumber is spec'd is that it is expected that it will have been dried to an appropriate MC for its service conditions. This is true if subsequent to kiln drying the material has been kept in or re-acclimated to an appropriate RH. "Kiln dried" lumber is often stored in unheated sheds that allow it to regain significant moisture subsequent to its sojourn in the kiln. "Air dried" often refers to lumber that has been dried outside to upwards of 10-12% MC. Lumber that is processed at that level,even if it is kiln dried lumber that has reabsorbed moisture from unfavorable storage conditions, and put into service in an environment with an average RH of 30-50%, is going to exhibit some undesirable movement. Kiln drying is not a magical process that imparts stability to lumber irrespective of its environment. Air dried lumber that has been acclimated to its intended service conditions is every bit as suitable as KD material for interior woodwork. Wood behaves like a sponge regardless of how it is initially dried.

[Mel Fulks]

Frederick, this has been covered many times and I have twice posted the test results of wetting and drying air dried and
kiln dried samples TAKEN FROM THE SAME BOARD, and in the tests of other scientists you will see the differences between
removing water from between the cells and from the cells. To your original question , if you know the difference between
the two types you will decide what's best ,based on the type of project with, no hesitency or doubt.

[John TenEyck]

I air dry most of the wood I now use. Where I live it stops drying at about 12 - 14% MC, then I put it in a dehumidification kiln that runs at 110F. Walnut dried this way has a lot more color and clarity than commercial KD walnut. Other than that, however, I see no difference with any of the other woods I've dried vs. purchased as KD. As others have said, dry is dry regardless of how you get there, and both processes can make junk if done poorly.

John

[Bradley Gray]

I use the same method: air dry/ dehumidification kiln. Sometimes the air dry part lasts long enough to not need the kiln. Kiln or no everything I store rebounds to around 10%. Commercially KD'd walnut is steamed which turns the sapwood dark (turns into FAS) thus the difference in the color of air dried.

[Larry Edgerton]

.you will see the differences between
removing water from between the cells and from the cells. .

Right there. That is an important detail.

Another reason that I prefer Kiln dried is beetle kill. I don't want to import powder post beetle to my wood room or someone else's home. I do use some air dried but not often.

[Kevin Jenness]

So-called "free water" is held between the wood cells while "bound water" is in the cell walls. When wood is dried below the fiber saturation point, about 28% MC, the free water is gone and the bound water starts coming out of the cells. This happens whether under a high moisture gradient in a kiln or a low gradient in the open air. There was a discussion on this subject on Woodweb a while back: http://www.woodweb.com/knowledge_base/Moisture_and_Wood_Movement_In_KilnDried.html

It is true that there is some decrease in reabsorption of moisture once lumber has been dried to a low MC, known as hysteresis; see http://www.cabinetmakerfdm.com/88415.html. (http://www.cabinetmakerfdm.com/88415.html.So)So perhaps it is fair to say that properly kiln dried lumber will initially move slightly less as it moves from 5 to 8% MC than air dried as it moves from 11 to 8%. And it does appear that high temperature kilning can cause changes to the wood cells that inhibit moisture caused movement to some degree, but it is also true that such high temps can cause the 'brittleness" that some associate with KD material.

Fundamentally, the important thing is to work with lumber that is in equilibrium with its expected service conditions, whether it gets to that point through air or kiln drying.

[Dennis Aspö]

We use kiln-dried pine in our company where I work (I work in the office though), we make wooden hot tubs and saunas. The kiln dried pine swells and shrinks less and behaves better, more like very old and dry wood. It is also darker in color, almost as if it had been treated with oil. Though it goes grey with sunlight exposure however and needs to be oiled yearly.

[David Weaver]

For hand work, especially with woods like fruit woods, I'd rather use air dried. I've always heard KD moves less than air dried though, and most of the wood I use is kiln dried.

A lumber guy dropped off wood for me at one point when I was making a dresser, and I showed him some KD wood that I had that was not very good (KD cherry) and his opinion was that it wasn't dried properly. I've had other KD cherry that was very nice, and didn't exhibit the sort of powdery latewood that the stuff I'm referring to exhibited (and each piece I get from the local lumber place is like that, it all comes from the same mill).

I wonder if some of the perceived differences are due to wood that just wasn't dried very well.

Also, I never really noticed anything until I started working wood by hand. A push through a TS, router and through some courses of sanding probably wouldn't have given me the same opinion as hand planing, scraping, hand sawing and rasping dooes.

[Curt Harms]

It seems like an advantage to kiln dried for commercial operators is uniformity. There is not likely to be a wet board or two in a batch of kiln dried like there might be in air dried. And no bugs like Larry mentions. I've checked air dried lumber stored in the basement with a moisture meter. This time of year when the heat's been on for a while it'll read 6%, just like out of a kiln. In the summer if we don't have a dehumidifier running it'll read 10%-12%. Just like kiln dried lumber stored on the same rack.

[Cody Colston]

"Kiln dried" is a pretty broad term. The type of kiln used and the method/skill of the operator are important aspects of kiln-drying lumber.

If the kiln is operated at 160f or higher the wood will probably be more brittle when machining, especially if the humidity in the kiln was very low. Perhaps that is how Krenov's lumber was kiln dried. However, a kiln can be operated to avoid this effect.

There are a lot of good reasons to kiln dry lumber vs air drying. It's faster, the color is brighter, there's less degrade, there's more control over the drying process, the heat will sterilize the wood (if heated to 133f at the wood core - not all commercial kilns heat the wood that high) the sap will be set, and KD will dry flatter than AD lumber of the same MC if the stacking procedures are good.

I think one has to weigh the advantages of kiln drying against the chance of slightly less workability and decide if air dried is best. However, even air dried must be placed in an environment (not outdoors) where the MC can be brought to 7% - 8% before working it. That makes it essentially the same as properly kiln-dried lumber...emphasis on "properly."

Of course, if you use kiln dried lumber, you can't say (in a superior tone of voice) "I only use air-dried lumber."