Kiln Dried vs Air Dried

[Jim Fox]

Is there any difference in working with kiln dried compared to air dried? I've only done my limited projects with kiln dried.

[Jim Becker]

No difference. What you want is "correctly" dried lumber...the method doesn't matter, frankly. Most of the lumber I use is air dried.

Some species, such as walnut, are better looking to many of us when air-dried as they typically get steamed when kiln dried to get higher yields and that removes a lot of the wonderful color variations.

[Neal Clayton]

that and some species prone to split will do so to a greater extent when force dried, rather than naturally dried. i primarily mess with old growth longleaf pine and it's one such species. lots more surface splits if you force dry it, not so much if you let it air dry.

[Chris Padilla]

We humans are an impatient lot! Mother nature likes to take her time to do things. However, we humans are a crafty lot as well! :) Usually slow and steady wins the race....

I think most have HEARD that air-dried walnut is superior in terms of color compared to kiln-dried walnut but I wonder how true it is. I don't think I've ever seen an "official" study one way or the other....

[Frank Drew]

I really like the quality and working properties of the native lumbers I've air-dried myself, but because of the realities of the marketplace I've used much more kiln-dried than air-dried and the work hasn't suffered for it.

[Jim Becker]

I think most have HEARD that air-dried walnut is superior in terms of color compared to kiln-dried walnut but I wonder how true it is. I don't think I've ever seen an "official" study one way or the other....

Easy to test...buy a piece of kiln dried/steamed walnut and a piece of air-dried walnut. Night and day when it comes to color and interest, at least to my eyes! The steaming makes both the sap and the heart the same "brown" color where the air-dried walnut has a tremendous variety of hues throughout from golden through deep purples and hints of green, depending on the particular tree and the conditions from which it grew.

[Cliff Rohrabacher]

If you are steam bending the wood, Air Dried is way better.
Otherwise it's just a question of moisture when you mill it.

[Chris Padilla]

Easy to test...buy a piece of kiln dried/steamed walnut and a piece of air-dried walnut. Night and day when it comes to color and interest, at least to my eyes! The steaming makes both the sap and the heart the same "brown" color where the air-dried walnut has a tremendous variety of hues throughout from golden through deep purples and hints of green, depending on the particular tree and the conditions from which it grew.


I guess I never know if the walnut I'm looking at is a.d. or k.d. My own personal stash is a.d. and does contain those wonderful purples and greens but not all a.d. gets this way.

[Chris Padilla]

If you are steam bending the wood, Air Dried is way better.

Why is that?

[Dave Lehnert]

If antiques are still around that were made before kiln drying. Air dry has to be a very good option.

[Jason Beam]

Why is that?

When kiln drying, the lignin between the celulose fibers tend to get more brittle. I'm not sure if it's a function of forced drying or overdrying or what. The steam (and other methods) of bending all do markedly better with air dried stock.

I think what happens is that with air drying, the moisture is free to find its own path out where a kiln makes for a lot of steam pressure inside the cells and this just rips those all-important connective tissues to shreds.

[Jim Becker]

Why is that?

Chris, kiln drying "modifies" the lignum (sp?) in the wood fibers because of the heat, which reduces it's ability to bend well when using moisture/steam to do so.

[Charlie Plesums]

Easy to test...buy a piece of kiln dried/steamed walnut and a piece of air-dried walnut. Night and day when it comes to color and interest, at least to my eyes! The steaming makes both the sap and the heart the same "brown" color where the air-dried walnut has a tremendous variety of hues throughout from golden through deep purples and hints of green, depending on the particular tree and the conditions from which it grew.

I believe you, but I wish I could get steamed walnut here in Texas. The stuff at the lumber yard has so much sapwood it is sometimes hard to identify as walnut. That is why I buy my walnut when we visit friends and family in Iowa/Minnesota. Not fun to bring 1000 pounds of lumber (the load limit my mechanic suggests for a 1000 mile trip) south each year

[Larry Fox]

Charlie, if you ever make it up to SE PA definitely take an empty truck to Hearne Hardwoods. Walk inside the big door and turn right, the 4/4,8/4 walnut in the bins there look like big wide slabs of dark chocolate. :) Tough to get mesquite up here though - gotta use hickory or apple in our smokers.

[Ben Davis]

Krenov's Art of Fine Cabinet Making goes into a small rant about kiln drying. At the time the book was published he was not a huge fan due to loss of color and texture in the wood. Just FWIW.

[Jack Briggs]

Kiln dried lumber's cell walls collapse after the evacuation of bound water, leaving a more stable structure; air dried lumbers have their cell walls more open and hence are more susceptible to moisture uptake. The age of the lumber has nothing to do with this exchange of moisture.

Every piece of air dried lumber I have in house will measure anywhere from 8-14% EMC with my Lignomat meter, vs. kiln dried measuring a constant 6-8% all year long. The variance with air dried lumbers is dependent upon the ambient humidity.


Cheers,

[Jim Becker]

Very true, Jack. That's why it's important that we all build furniture, etc., using techniques that accommodate wood movement. Changes in moisture seasonally are less of an issue at that point. And there are certainly some applications where stability might be more critical...perhaps in your particular business...that are best served by kiln dried material.

[Cody Colston]

Krenov's Art of Fine Cabinet Making goes into a small rant about kiln drying. At the time the book was published he was not a huge fan due to loss of color and texture in the wood. Just FWIW.

Krenov also discussed air drying vs kiln drying in "A Cabinetmaker's Notebook." He was of the opinion that kiln dried wood was "dead" and also stated that his lumber was never completely dry, even though some of the planks had stood in his shop for seven years or more before being worked.

Since Krenov hand planed his stock, he was more concerned with the workability of it and could easily tell the difference between air dried and kiln dried just by feel...no moisture meter required.

For electron burners, more concerned with stability than workability, kiln dried is probably superior. For those few who are really intimate with the wood and how it works with hand tools, then air dried is likely preferable.

[Prashun Patel]

Thought I read something about kiln dried wood kills all fungus that could spalt/rot wood. Air drying doesn't necessarily. I'm not saying that's a high risk, though.

[Chris Padilla]

Great stuff...never knew such differences existed betweed kd and ad wood!

[Jim Becker]

Thought I read something about kiln dried wood kills all fungus that could spalt/rot wood. Air drying doesn't necessarily. I'm not saying that's a high risk, though.

Air drying gets the wood below the moisture level that will support fungal growth, too. Most air dried material is in the 8-12% MC (in general), depending on geography. Around here, it's 10-12% for my stock. That's well below what you need to support rot and fungal growth.

[Paul Greathouse]

One thing I haven't seen mentioned yet is the possibility of wood beatles or some other insects in air dryed wood. Some of the local proponents of kiln drying that I know have warned against using air dried lumber for large projects such has kitchen cabinets for this reason.

I had alot of conversations with the head building inspector for our parish when we were building my son's house last year. He claims that his uncle was a cabinetmaker and had used some air dried red oak to save some money on a job once. Several months after the job had been completed the customer called back wanting to know why sawdust had suddenly appeared on her countertops. Supposedly wood beatles can lay dormant in wood for several years and then decide to come to life and bore out.

I don't know how true this is, I've worked with alot of air dried wood on smaller projects and didn't have any problems but his story was enough for me to have a 1000 bdft of red oak kiln dried for my son's cabinets before I built them. I had built the cabinets in my own house twenty years ago out of air dried cypress. No insect problems but I do have some joint separation.

All of the other proponents of kiln drying that have warned about the fact of insects in air dried wood "had a dog in the fight" (they were kiln operators). The inspector didn't, he had previously been a plumber. He gave me loads of valuable plumbing info while I was plumbing my son's house so I had no reason to doubt the credibilty of the story about his uncles beatle snafu.

Does anyone have any facts about possible insect infestation in air dried wood?
How long can they lay dormant?
How many different varieties are there?
Is the possibility of them being there more prevailent in certain areas of the country?
How much damage do they really do?
Is there some other way of killing them, other than kiln drying?

[Charlie Plesums]

I built a pecan (hickory to yankees) table for a customer, using all lumber-yard kiln dried wood. The 2 inch thick legs (10/4 or 12/4 - don't recall) started creating sawdust a year later. Baking them in the Texas Sun (over 130 degrees) for half a day didn't solve the problem. Go figure. I will be replacing the table legs.