Air dry vs. kiln dry

[Bmac]

Obviously I am not going to change your "opinion". I attempted to educate the difference which is significant and on a cellular level. If you wish not to believe proven science then that is your right. I will not debate you further. You stated in your first post that you believed others may have more information; however your ego fails to let you hear and understand. Keep doing what you do but please do not spread bad information on a topic you obviously to not totally understand. You have proven once again that the forums are full of misinformation.

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Funny thing is you actually could CHANGE my opinion if you showed me the scientific data you say you have.

I did say in my first post that I believed others may have more information and I would love to learn. This exchange has stimulated me to do further research.

So let me say that I did find that your original statement does have some truth to it, under certain circumstances. I'd like to dispel any misinformation.

If you look at kiln drying lumber, you find it is a relatively new process to the centuries of woodworking. It's big commercial advantages are that it reduces weight for shipping, sets pitch in pine, and effectively kills any insects in the lumber. It can effect lumber quality if not done correctly.
There are many ways to kiln dry; solar, steam heat, low temp, high temp, compression, vacuum, dehumidifying, and probably more that I missed.

What I found was that kiln drying at high temps will actually change the cellular makeup and reduce the hydroscopic ability of the wood to take up moisture.
So you are absolutely correct in that instance and I've learned something!

It appears though that the other methods of kiln drying do not affect the hydroscopic nature of the wood like high heat kiln drying does. The key seems to be if you want to reduce the hydroscopic nature of wood than you need to dry at high temps. So in affect we are both correct, depending on the method of kiln drying.

Here are some sources that look into high heat methods of kiln drying;
https://www.fpl.fs.fed.us/documnts/pdf1960/mathe60a.pdf - look in the conclusion, high heat reduces the hydroscopicity differently than other kiln drying methods
https://www.scionresearch.com/__data/assets/pdf_file/0009/58932/NZJFS611976KININMONTH101-107.pdf - In the abstract, there is a progressive reduction of swelling and moisture uptake as drying temperature is increased
http://citeseerx.ist.psu.edu/viewdo...6C9C386?doi=10.1.1.666.8647&rep=rep1&type=pdf -- another showing the relationship of drying temp to hydroscopicity
https://link.springer.com/article/10.1007/s40725-016-0034-z -- overview of kiln drying -- some evidence that high temp drying will close off some cell walls

So lets hope this interaction, in a small way, helps spread correct information on these forums. I've shown research articles, both scientific and summary statements to prove my side of the argument and to prove your side of the argument.
Waross, perhaps you would like to add to this? Would love to see your scientific data also. I understand my info was just gained in a superficial web search and you may have information I was not able to access.

 

[rarefish383]

When I went to the University of MD under a Botany major, many of our courses were based on the studies of Dr. P.P. Perone. There was a new fellow on the block by the name of Dr Alex Shigo. Some of his studies were being taught, or at least looked at, like CODIT. If the studies of Perone were later proved by Shigo to be incomplete, or flat out wrong, does that make my degree invalid. I put in my time at Md, and then 40 more years in the tree care industry. If we treated trees using Perones teachings, and they were proven wrong, why, now, almost 50 years later, are they still standing. One must be careful when presenting scientific fact to the general public, because those facts are often limited to the environment they were tested in, and if they are 99.9 percent accurate, someone will find that .1 percent exception. As soon as I saw the word "Limits" used, I thought, Oh,Oh, here we go, someone is going to find the exception, and they did. I quit thinking, and trying to prove, I was smart when I realized that every bit of knowledge in the universe is already there, we just haven't found it yet, Joe.

 

[Sawyer Rob]

My wife tell me that I have a BS in a lot of subjects and I didn't even have to go to school to get it... lol lol

MY Cabinet making career (I owned/ran my own custom furniture/cabinet shop) tells me, that when I bought kiln dried lumber and built furniture out of it, that AFTER it was built, "IF" the RH went up, the furniture "moved"... Just like the same species did when I "air dried" the lumber that I also used from time to time.

In MY experience, kiln drying lumber does NOT STOP wood movement when the RH changes, I don't care what a book says, it happens, I've seen and dealt with it myself as a professional furniture/cabinet maker...

SR

 

[BigOakAdot]

This doesn't really apply too much to this comparison but relates to humidity I assume.

I made a checkerboard style walnut/cherry cutting board. Got a pure tung oil finish on one side and set it aside for quite come time. (Tends to happen to a lot of my projects lol)

I then pulled it back out and had it laying in my room where my wife decided to stick it on the window sill ‍ Right when I saw that I knew it had gotten at least 4 hours of direct sunlight. The thing mine as well been a curved bar seat when I picked it up.

Was very upset about it and don't you know the next humid day (summer in philly area is super humid) the thing went right back to where it was.

It was air dried so I'm sure it wasn't super low moisture content and played a large roll. Just thought it was an interesting story when it comes to wood
Movement. It's now at my uncles and seems to be holding up just great in his kitchen.

 

[bowtechmadman]

Wow some interesting reading.
A little off topic but I think it applies to the little jousting contest presented by Mr. Academia. Dr. Larry Nassar was once thought of as being the most renowned Osteopathic Dr's in the nation. Now he's in prison for where he belongs for molesting countless athletes. Just because someone say's it's true and right it might not always be the case.

 

[Bmac]

My wife tell me that I have a BS in a lot of subjects and I didn't even have to go to school to get it... lol lol

MY Cabinet making career (I owned/ran my own custom furniture/cabinet shop) tells me, that when I bought kiln dried lumber and built furniture out of it, that AFTER it was built, "IF" the RH went up, the furniture "moved"... Just like the same species did when I "air dried" the lumber that I also used from time to time.

In MY experience, kiln drying lumber does NOT STOP wood movement when the RH changes, I don't care what a book says, it happens, I've seen and dealt with it myself as a professional furniture/cabinet maker...

SR

Words of wisdom from someone who has firsthand experience; ignore wood movement and you'll have unhappy customers or go out of business.

 

[AZWoodworker]

Obviously I am not going to change your "opinion". I attempted to educate the difference which is significant and on a cellular level. If you wish not to believe proven science then that is your right. I will not debate you further. You stated in your first post that you believed others may have more information; however your ego fails to let you hear and understand. Keep doing what you do but please do not spread bad information on a topic you obviously to not totally understand. You have proven once again that the forums are full of misinformation.

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I could understand not arguing with some guy in a bar, but on a forum, it is a place to educate and I for one would like to be able to look at the studies or data and have a definitive statement. I am looking to move My furniture online to sell in more high moisture content states. I have thousands of board feet of rough lumber that have been air-dried in Arizona. I don't have a high-end moister meter to go deep into the wood but when opened I get about 10 percent. If I am building and shipping to high humidity, I can build for expansion, but I still would like some definitive answer for vulnerable procedures on stocks. In looking at data all wood acclimates to the moisture content of the area. I have no other data that refutes this because science or those that have degrees seem to give the answer of "believe proven science". Science is a method. The observation, identification, description, experimental investigation, and theoretical explanation of phenomena. or another more structured definition; A systematic method or body of knowledge in a given area. Armchair quarterbacks trying to understand things. You will be surprised how much this statement is given if you don't believe it... Sounds like it is a trained statement in universities. I went for engineering but never took that class.

I am not trying to be critical, but some studies and experiments would be great. An expert should be able to educate instead of taking his blocks and going home.

 

[Sawdust Man]

Watch out for "education" and "degrees"!!!
There is no classroom substitute for real world experience, and "scientific facts" are only facts if they are in fact true.
If wood moves by being exposed to increased humidity after being kiln dried, then it does, doesn't matter what some guy with letters after his name says.
The cellar structure probably is changed during kiln drying, but change doesn't necessarily mean a real improvement.
I think most true experts are the folks who make a living at a thing, not those who get paid to talk about it.
Personally I'd much rather be taught by doers than talkers.

In my 35 years of sawmill and cabinet shop experience, I have had very poor success with air drying lumber, and therefore I prefer kiln dried wood.
Over the years, we have lost thousands of bf to bugs and mold / stain, trying to air dry lumber in the PNW, in other climates it may be more doable, climate makes a big difference with wood handling.
After 43 years working with lumber in the pnw, I'm now in Missouri, so I have to re learn how it's done here.

My advice is to find folks in your climate who's living depends on the methods they use, and learn from them, they are the true authorities on the subject.

 

[blades]

Generally kiln process is to take it down to 6-8% then stack for awhile and let it stablize, around 12%. Now if shipping wooden products interstate or anywhere else in the world it must be kiln dried or at the minimum heat treated to kill bugs. heat treatment does little to dry the wood. Your air dried product will still have to be heat treated by some co. that is certified in that.

 

[AZWoodworker]

Generally kiln process is to take it down to 6-8% then stack for awhile and let it stablize, around 12%. Now if shipping wooden products interstate or anywhere else in the world it must be kiln dried or at the minimum heat treated to kill bugs. heat treatment does little to dry the wood. Your air dried product will still have to be heat treated by some co. that is certified in that.

Thank you. Any more information on that? Is there an interstate law on that that you are aware of? I have not seen bugs beyond the bark which I remove if I see any, and have milled some Ash that had worms, but separated this from other wood and killed them. Are there other bugs I would be missing in the wood? I made enough with what I have dried into pieces for furniture and other wood items and kept a close eye on anything that might be bugs as I cut. So I have experience with my procedure. This does not mean I would be able to discover eggs that would hatch in a more moist enviroment.

I live in Arizona. I have built many things with air-dried, but only locale and minimum, but lots of personal or friend projects. When I air dry it is off the ground, has metal roofing on top, stickers are 1.5 inches at 18 ins to 2 ft, and the temp gets to 115 or higher in the sun, ( A lot higher sometimes I feel like I landed on Mars) and I check the wood often for any bugs. I do try to remove bark as I can based on what I am milling and how easy it is to do at the time, and I mostly mill into 2 1/2 in slabs but even after a bit I go back and knock off bark where I can. I've checked with UV routinely and found scorpions so I now have Geckos throughout the backyard that eat them. I love milling logs, and moving around heavy 10 or 16 footers and do it mostly with chainsaws. I also have local bandsawyers that I do loads now and then. Where any bugs come in on the logs or are seen in bark I chemical kill. I mill Mesquite, Chinese elm, Rosewood, Russian Olive, Afghan Pine, Mulberry, and ash mostly from urban areas.

I need to check any laws on exporting out of state and maybe need to include a disclaimer that the wood is air-dried, and deal with it in Marketing ensuring customers know. However, if there are laws that prevent transfer even the possibility of bugs, then need to build a kiln. If it needs to be certified then have to find and use a certified kiln or get certified myself, which sounds horrid.

My normal job is being hammered in the fear of Covid and I need to put this production into place or ...

 

[blades]

Yes there various state and federal laws on wood product transportation across state / county lines as well as for international shipping. These all require at the minimum heat treatment protocols. The Ash borer is a classic example of why these protocols are now in place. By the way this extends to firewood as well. A simple disclaimer will not protect you from the wrath of Federal or State regulation agencies.

 

[blades]

Not real difficult to build a kiln but pricy. there are a set of time lengths to maintain various temps in the kiln. certification requires it to be inspected and certified by agency to those parameters.