Will kiln dried lumber return to normal % moisture?

[Andy Pratt]

I was recently watching a woodworking video where an experienced woodworker inferred that kiln dried lumber will never get back to the moisture level of air dried lumber, even after decades of sitting around. He mentioned that it stays in the 6-8% range instead of 12% like air dried wood.

This doesn't seem to make sense. I would think wood at 6% moisture, placed in an area with 12% moisture, would get back up to 12% over the years. Does kiln drying chemically alter the wood and prevent this from happening, or was this individual incorrect?

Along these lines, it was also mentioned that air dried wood "moves more" and is less suitable for furniture in today's modern, humidity controlled homes (inference was that there is a lower moisture content in the air in the house, presumably more toward 6% than 12%). All this sounded a little sketchy to me, more like marketing hype than reality, so I wanted to get some real-world opinions.

Thanks in advance for the replies,
Andy

[Howard Acheson]

Wood, whether initially air dried or kiln dried, will always move to it equilibrium moisture content (EMC) relative to the relative humidity. In other words, wood at 4-6% EMC will move to 8-10% EMC if it is moved to an environment of 50% relative humidity.

He didn't know what he was talking about.

[Chris Padilla]

Andy,

Maybe you heard him incorrectly? I have a hard time believing that an experienced woodworker would say that. All that kiln drying does is speed up the time of getting the wood down to a usuable range for building furniture with. Yes, it has other affects like changing colors (esp. in walnut) but it doesn't alter the wood in a way that it won't absorb moiture agian and therefore stop moving! If it did, it would be a revolution and a boon to woodworking all over the world to know that your solid wood projects no longer move!!

Who said this? What video? :)

[Richard Wolf]

I would believe that once it is Kiln dried the cell walls are no longer as elastic as they are when air dried. They then lack the ability to reabsorb moisture. This is why air dried lumber is much easier to steam bend then kiln dried, the air dried lumber absorbs the steam moisture much better. MHO.

Richard

[Frank Drew]

The fellow mispoke.

I agree with Richard, though, that wood's ability to absorb moisture diminishes over time with the effects of age and cellular collapse. Kiln drying might speed that up, but I think the point was overstated in the video. If you put a piece of kiln-dried lumber in a rain forest it will pick up moisture.

[Jim Becker]

This is why air dried lumber is much easier to steam bend then kiln dried, the air dried lumber absorbs the steam moisture much better.

A lot of this is relative to the lignum in the wood...kiln drying "sets" it and it becomes somewhat inelastic even when steamed. This damage is not present in air-dried or green wood.

[Steve Schoene]

Apparently, hysteresis in moisture content levels is a reality in kiln dried woods, so that in fact they do not absorb moisture to the same degree than air dried wood at the same humidity levels. Apparently the magnitude of the effect depends, among other things, on kiln temperatures during the drying. There is some research that shows this effect based on experiments with spruce.

http://www.skogoglandskap.no/filearchive/gjerdrum_helsinki07.pdf

This does not mean that we can ignore wood movement in construction design, but it is interesting and suggests. that the video mentioned by the o.p. has a kernel of truth in it, though I doubt it is to the same degree as mentioned. Note however that even if the hysteresis is a "temporary" a significant enough lag in the return to Moisture Content that would have been achieved air dried wood, given a fluctuating environment (as seasons fluctuate) could actually prevent the wood from ever really achieving the EMC that it would have achieved without the kiln drying.

In a sense, it is similar to the effects of finishes on furniture. A finish that resists moisture vapor transfer keeps the equilibrium level considerably lower, than bare wood. Hoadley shows this in his chapter 5, figure 2, in my 1980 edition.

I googled hysteresis wood moisture to get this info. I had to look up hysteresis-- here is the most accessible definition I found in a brief search:

Hysteresis is a physics (http://knowledgerush.com/kr/encyclopedia/Physics/) term that means, literally, to be late. It describes systems that do not directly follow the forces applied to them, but react slowly, or don't return completely to their original state: that is, systems whose states depend on their immediate history. For instance if you push on a piece of putty (http://knowledgerush.com/kr/encyclopedia/Putty/) it will assume a new shape, and when you remove your hand it will not return to its original shape, or at least not entirely. Source: knowledgerush.com

[Tony Joyce]

Yes, it has other affects like changing colors (esp. in walnut) but it doesn't alter the wood in a way that it won't absorb moisture again and therefore stop moving! :)

Chris,
What is the source for this information? I've never seen that stated before. Steaming walnut(also sometimes cherry) is a - separate process - that must be done prior to drying. Or so I've been told by the people that do it. If the logs lay too long before processing(sawing and/or steaming), steaming is not as successful. This would seem to be true based on what I've seen.

Unsteamed kiln-dried walnut looks just like air-dried. This I have observed for myself by handling both types of lumber on an almost daily basis.

Tony Joyce

[Tony Bilello]

......."was recently watching a woodworking video where an experienced woodworker inferred that kiln dried lumber will never get back to the moisture level of air dried lumber, even after decades of sitting around. He mentioned that it stays in the 6-8% range instead of 12% like air dried wood. "

There are two layer of water in wood. Think of the cells in wood as a soda straw. Air drying dries out the moisture in the cells or soda straw. This is called "free water". There is also moisture trapped in the cell walls themselves. This is called "bound water". This is the extra moisture that kiln drying will get to and air drying wont. A kiln is not just an oven. It provides regulated air flow and a vacuum of sorts. I dont know if the wood would remain in the 6-8% range because it will absorb a certain amount of water back into the soda straw cells, but I dont think it would get back up to 12% except near the surface exposed areas.

I build high end furniture on commission and I would never use lumber that was not kiln dried. Most antiques will eventually split and dry out when put in a modern heated and air conditioned home but most modern wood furnitue will not be affected by moisture if put in the garage. If there is any hype at all about kiln drying, its by the local sawyers that dont own kilns.

Logic dictates that if kiln drying wasnt necessary, furniture manufacturers wouldnt go for the extra cost.

[Jack Briggs]

I would believe that once it is Kiln dried the cell walls are no longer as elastic as they are when air dried. They then lack the ability to reabsorb moisture. This is why air dried lumber is much easier to steam bend then kiln dried, the air dried lumber absorbs the steam moisture much better. MHO.

Richard


Bingo! This is the correct answer.

Kiln drying causes a collapse of the cell walls, inhibiting the rehydration of the cells at later time. Air dried lumber's cell walls are intact, retaining it's hygroscopic nature.


Cheers,

[Larry Edgerton]

I too will not waste my time or take a chance with my professional reputation by using air dried lumber.

Another point not brought up is that a kiln kills all organisms living in the wood such as powder post beetles, etc.

Kiln drying is a science, each species requiring a slightly different approach. Do some research and it will help you better understand wood.

The man's statement was correct.

[Jim Becker]

Larry, lots of very famous folks have been building masterpieces out of air dried lumber for thousands of years...

That said, kiln dried lumber is great to work with and yes, depending on the method used, it can also help deal with critters.

[Clifford Mescher]

......."was recently watching a woodworking video where an experienced woodworker inferred that kiln dried lumber will never get back to the moisture level of air dried lumber, even after decades of sitting around. He mentioned that it stays in the 6-8% range instead of 12% like air dried wood. "

There are two layer of water in wood. Think of the cells in wood as a soda straw. Air drying dries out the moisture in the cells or soda straw. This is called "free water". There is also moisture trapped in the cell walls themselves. This is called "bound water". This is the extra moisture that kiln drying will get to and air drying wont. A kiln is not just an oven. It provides regulated air flow and a vacuum of sorts. I dont know if the wood would remain in the 6-8% range because it will absorb a certain amount of water back into the soda straw cells, but I dont think it would get back up to 12% except near the surface exposed areas.

I build high end furniture on commission and I would never use lumber that was not kiln dried. Most antiques will eventually split and dry out when put in a modern heated and air conditioned home but most modern wood furnitue will not be affected by moisture if put in the garage. If there is any hype at all about kiln drying, its by the local sawyers that dont own kilns.

Logic dictates that if kiln drying wasnt necessary, furniture manufacturers wouldnt go for the extra cost.
Interesting topic. If memory serves me properly, Tony's explanation sure rings a bell. Clifford.

[Tony Joyce]

.......
Logic dictates that if kiln drying wasn't necessary, furniture manufacturers wouldn't go for the extra cost.

Yes but, economics would make up for the cost of drying. Meaning, sitting on inventory for the time required to air-dry. 30 days versus 1-4 years. Time is money in manufacturing.

Tony Joyce

[Chuck Tringo]

Bingo! This is the correct answer.

Kiln drying causes a collapse of the cell walls, inhibiting the rehydration of the cells at later time. Air dried lumber's cell walls are intact, retaining it's hygroscopic nature.


Cheers,

I'm not sure I agree with this statement 100%...if this were the case then you would assume that everyone who used kiln dried lumber wouldn't have to worry about wood movement when planning/building their projects, but we know that no matter how the drying is done, wood will still move. I do have to say that I like the idea of killing off all of the critters, but not sure I buy the lack of re-hydration...just my 2 cents

[Clifford Mescher]

Yes but, economics would make up for the cost of drying. Meaning, sitting on inventory for the time required to air-dry. 30 days versus 1-4 years. Time is money in manufacturing.

Tony Joyce
That would be a factor for only the first batch...Cycling would eliminate any waiting. Clifford.

[Tony Joyce]

While I do agree cycling would kick in. The problem(for manufacturers) is that demand by species and volume is somewhat consumer driven. Meaning you would be sitting on a large amount of raw materials to hedge all bets. Not being able to know which species or how much would be needed down the road, would translate into usable capital sitting on a lumberyard somewhere. Also extra capital needed for storage facilities.
Of course this concept would really only apply to larger manufacturers. While I respect everyone's opinion, My personal believe is kiln-drying is not detrimental to lumber. Since we are in a need-it-yesterday era kiln-drying would seem to help fulfill this need also.

Tony Joyce

[Richard M. Wolfe]

Kiln drying provides a much greater amount of control over the drying process. Some woods, like maple or holly, need to have the moisture removed as fast as possible, taking into consideration checking. If fresh sawn wet oak is subjected to immediate hot dry conditions it is prone to checking, honeycombing or case hardening. Considering the difference of summer to winter or extended wet or dry conditions, a more uniform product in much less time can be produced by kiln drying. Wood suppliers wouldn't do it if it weren't worth doing, considering the cost of running a kiln, much less the initial capital outlay.

[Rick de Roque]

I too will not waste my time or take a chance with my professional reputation by using air dried lumber.

Another point not brought up is that a kiln kills all organisms living in the wood such as powder post beetles, etc.

Kiln drying is a science, each species requiring a slightly different approach. Do some research and it will help you better understand wood.

The man's statement was correct.

He mentioned that it stays in the 6-8% range instead of 12% like air dried wood.

That is not a true statement. Kiln dried lumber will not stay in the 6 to 8% range if exposed to higher RH. Read Hoadley, R. Bruce (2000). Understanding Wood: A Craftsman’s Guide to Wood Technology for a better understanding of the subject.

Rick

[paul dyar]

What happens if you put air dried wood in a kiln?
What happens if you put air dried wood in a modern house with air-condition where the humidity is very low, providing you do not have a humidifier. And how many homes have humidifiers?
paul

[Clifford Mescher]

While I do agree cycling would kick in. The problem(for manufacturers) is that demand by species and volume is somewhat consumer driven. Meaning you would be sitting on a large amount of raw materials to hedge all bets. Not being able to know which species or how much would be needed down the road, would translate into usable capital sitting on a lumberyard somewhere. Also extra capital needed for storage facilities.
Of course this concept would really only apply to larger manufacturers. While I respect everyone's opinion, My personal believe is kiln-drying is not detrimental to lumber. Since we are in a need-it-yesterday era kiln-drying would seem to help fulfill this need also.

Tony Joyce
I'm not arguing pro's and con's, merely making statement. I. personally do not have much experience with air dried lumber. Hasn't been an option where I live. Clifford.

[Frank Drew]

From some of the posts, I have a sneaking suspicion that some of those categorically opposed to using air dried lumber don't in fact have much experience with it.

I was quite comfortable using both kiln- and air-dried wood in my "high-end furniture" business, and never had a call back due to wood splitting or other such unhappiness, nor have I seen those effects in the work I still have occasion to see, many years later.

Additionally, I've had kiln-dried lumber attacked by powder post beetles, particularly ash.

Modern furniture manufacture (the large scale operations) is all about kicking the work out the door as fast, and as inexpensively, as possible; I don't think we want to be holding them up as models of the best work possible.

[David Keller NC]

The statement related by the OP, at least from the standpoint of the equilibrium moisture content, is incorrect. From engineering mass-transfer and equilibrium principles, this not actually possible (kiln-dried "staying" at 6-8% and air-dried not going below 12%).

It is possible that the speed at which the wood reaches its ultimate equilibrium moisture content when exposed to a particular % relative humidity could be different because of the potential changes to the structure of the wood at the higher temperatures it's exposed to in a kiln.

But, I can assure you from specific measurements that air-dried wood, will, if kept in a low-humidity environment over a period of a multiple months or years, indeed fall far below 12% moisture content. And given sufficient time, both kiln-dried and air-dried wood will reach an almost identical equilibrium moisture content because they share the same chemical composition.

Moreover, the free water in either kiln-dried or air-dried lumber is gone very quickly. It is a significant fraction of the "bound" water that must be removed, either by high temperatures in a kiln (fast) or by exchange with an outside environment (slow) that is required to make wood usable in a furniture situation.

It is also incorrect to state that a modern home is "drier" than a home in the days before forced-air heating or air-conditioning. That depends a lot on the location; a home in Arizona in the 1800's was quite a bit drier than any home in a coastal area, almost any time of the year. Moreover, anyone that lives on the East Coast recognizes that during the winter, a front coming in from the Northwest may plunge outdoor relative humidities to well below 15%, and when that air is heated (as it would have been in a home before forced air heating), its relative humidity will drop even lower. That's dry, no central heat required. Moreover, a modern home, even in the winter, is likely to have appreciable humidity levels despite the central heating because they have running water. Washing dishes, taking showers, doing laundry, etc... will all boost the humidity levels well above what they would have been in a fire-place heated home in the 18th or 19th centuries, when the only water in use was likely to have been a pitcher setting quietly on a dry sink.

Finally, one must recognize that a fair number of antiques are cracked for considerably more complex reasons than that they used "air-dried" lumber. Many of these antiques were built with cross-grain construction, the cabinet shops of the day did not always carefully season their wood (so it would've definitely been "wet" by our modern standards), and in many cases these antiques are jerked from an outdoor storage location and placed directly in an air-conditioned space when they're "discovered". As many of us can attest, rapid humidity changes often result in cracking or checking. Slower humidity changes do not.

[Tony Bilello]

What happens if you put air dried wood in a kiln?
What happens if you put air dried wood in a modern house with air-condition where the humidity is very low, providing you do not have a humidifier. And how many homes have humidifiers?
paul

If you put air dried wood in a kiln, the moisture content would be further reduced and the higher temps in a kiln (160 degrees sustained) will kill powder post beatles and many other pests that air drying wont. As a side note, lumber is usually not directly put into a kiln right after it is sawn. It is usually air dried for about 30 to 45 days typically in which it loses a great deal of its moisture.

If air dried wood is put into a modern home where the humidity is low it will probably lose a little more of its moisture content.

Also note that in days of old much of the wood was air dried in the open for a period of time and then it was usually moved up to the top area of a barn where it was very hot and ventilated. Way back when, the typical sawyer that supplied lumber for furniture didn't produce lumber in large quantities. Up until modern times (the age of inexpensive furniture) there was not a great demand for furniture. Furniture was made for the upper classes. The average person scrounged lumber when and where he could and literally just slapped it together. That is the 98% of the furniture that didn't survive.

[Cody Colston]

James Krenov has furniture in private homes and museums all over the world and he worked exclusively with air-dried lumber. I don't believe his pieces have cracked and fallen apart.

In fact, in his opinion, kiln-dried wood was "dead." He says that it was brittle and did not work with hand tools the way air-dried lumber did. Of course, hand planing all his pieces the way he did, he was much more in tune with how the wood worked than a mainly electron burner would be.

If wood movement is accounted for in the construction of a piece (and it should be) I don't see where it would make that much difference using air-dried or kiln-dried.

I do know that kiln dried lumber will not stay at 8% MC if subjected to higher humidities.

[Curt Harms]

I do know that kiln dried lumber will not stay at 8% MC if subjected to higher humidities.

True statement, and I have some air dried stock in the basement that after a few months of heating season reads 6% on my mini Ligno. Will it be 6% next august? Nope. Neither will a stick of K.D. maple that's been there for several years.

Curt

[Jim King]

Here in the Amazon we have been working with the hardest , densest woods in the world for many years. We kiln dry 5/4 down to 5-8 % normally in 20 days. If it is not processed and shrink wrapped it will regain moisture to 17-19% in a few months.

Tropical woods are easier to dry than oak as to time, degrade etc . even while many are much harder and denser than oak. If a peice of furniture is built here out of air dried mahogany which is soft or any other species it should not be sold to a customer who has air conditioning or it will self destruct.

I would not attempt to be in the wood business without kilns as here it is not possible to make money selling green rough lumber.

[Dewayne Reding]

Can anyone post pictures of a piece of furniture built in say the past 20 years, that you know with certainty was constructed of air dried lumber, and has subsequently self destructed indoors? There are many people using air dried lumber, so I am, thinking these failure examples should be easy to should be easy to find if it's not just a myth. In my mind, a hundred year old cracked up antique is not very good "evidence" since we don't know if the piece was built with wet lumber, or some other extenuating circumstance such as poor storage or technique that may not be apparent.

I'm very curious to see what these failures look like because I have some DIY oak and walnut air drying now, and am considering buying some more I didn't cut.

[Frank Drew]

If a piece of furniture is built here out of air dried mahogany which is soft or any other species it should not be sold to a customer who has air conditioning or it will self destruct.

But working with any wood, you should bring it into an indoor environment well ahead of working it up so that it won't self-destruct when it goes into another indoor environment. One reason to air-condition your shop, apart from operator comfort.

And that's why they invented moisture meters.

[Steve Rozmiarek]

James Krenov has furniture in private homes and museums all over the world and he worked exclusively with air-dried lumber. I don't believe his pieces have cracked and fallen apart.

In fact, in his opinion, kiln-dried wood was "dead." He says that it was brittle and did not work with hand tools the way air-dried lumber did. Of course, hand planing all his pieces the way he did, he was much more in tune with how the wood worked than a mainly electron burner would be.

If wood movement is accounted for in the construction of a piece (and it should be) I don't see where it would make that much difference using air-dried or kiln-dried.

I do know that kiln dried lumber will not stay at 8% MC if subjected to higher humidities.

Many people respect Krenov, while others think he is a joke. Statements like that one from him shore up my leanings toward the later. Wood is wood, its all a little unpredictable, and may very well splinter or be brittle, if it was the nature of the tree. That's one of the perverse pleasures of using it.

While I have not yet invented a completely useless piece of furniture to ride to fame, I do use both air dried and kiln dried, both with planes and chisels, and I don't think there is a difference. Maybe I'm just not in tune enough with something.

No disrespect intended to those of you who draw inspiration from Krenov, he just dosen't give me any.

Cody, your point is a good one though, that would be an obvious failure of air dried if his pieces started failing.

[Alex Shanku]

Many people respect Krenov, while others think he is a joke. Statements like that one from him shore up my leanings toward the later. Wood is wood, its all a little unpredictable, and may very well splinter or be brittle, if it was the nature of the tree. That's one of the perverse pleasures of using it.




Oh boy...

What schools of woodwork have you founded?

How many books have you published?

Your work is in how many museums again??

The joke here doesnt appear to be Krenov......

[Frank Drew]

Steve,

I have a lot more experience with kiln-dried than air-dried lumber because that's what's most available commercially, but in my somewhat limited experience, air-dried seems milder cutting and working. I don't know if it's always that way, or has to be that way due to something in the nature of kiln-drying (or hurried kiln-drying perhaps), but that's been my experience.

[David Keller NC]

"While I have not yet invented a completely useless piece of furniture to ride to fame, I do use both air dried and kiln dried, both with planes and chisels, and I don't think there is a difference. Maybe I'm just not in tune enough with something."

I have similar experience - using both air-dried and kiln-dried wood. I have built several pieces each with both air-dried and kiln-dried walnut and red oak, mostly with hand tools, and have not found any difference between the air-dried or kiln-dried material when it comes to workability.

I will, however, defer to those that make note of a difference between the two when it comes to steam-bending, I've just not done enough to form an opinion in this specific circumstance.

I'd also note that Krenov most certainly approaches the craft from an emotional perspective, while others of us with different training are more interested in rational thought reduced to numbers and measures. That doesn't mean Krenov's wrong in regards to his preferences for wood, just that his perspective may well be different, with different criteria applied.

In my particular case, I don't have any interest in the provenance of the tree - it matters little to me if it was cut from an historic site, or was a temple tree, or just came from some woods on the back 40. Those with Krenov's perspective may think very differently along these lines.

[Cody Colston]

David and Steve,

Your opinions of Krenov are certainly your own and no business of mine. The point I was trying to make was that he worked with air-dried lumber and his pieces have not failed to my knowledge...in multiple and diverse locales around the world.

Jim King...Krenov also had a friend in Brasil (Sau Paulo) who regularly shipped him Amazonian hardwood...air dried.

The key to working it was that after it had air dried for a couple of years, Krenov then moved it into his shop where it was often kept for seven or more years prior to being worked. I don't know what the MC was by then but I'm sure it was pretty low.

I've also worked both air-dried and kiln-dried lumber with chisels and planes. I can't tell the difference between them, either. But, someone who worked exclusively with hand made planes would likely develop a feel for that difference, even though it is slight.

This is an interesting thread, even though it has morphed away from the OP's question. Imagine that!

[Steve Rozmiarek]

Oh boy...

What schools of woodwork have you founded?

How many books have you published?

Your work is in how many museums again??

The joke here doesnt appear to be Krenov......

Figured that'd rile up a few:D

Alex, if you like Krenov fine, that's your business, I don't and the reverse applies.

Following your critera, no one would have the right to criticise unless one has identical experiance, no? Ok, then you need to apply that theory to all facets of life, not just Krenov to be fair. No comparing cars until you build your own, no criticising your boss until you've done his job, no voting until you have done the work of each of the politicans. That's all as absurd as your statement. Also to follow your logic, Norm is far more inspirational then Krenov. Which I'd actually agree with.

Schools? They are just another way to derive income from this hobby/profession. Do you follow lockstep with every teacher you ever had? I doubt that the good ones would have wanted you to.

Published books? Time Life publishes many books every year, and a significant portion of them are junk. Books are just another way to get income out of this business/hobby.

Work in museums? There is a cross in a jar of urine in a museum. Time will assign a legacy, not a museum.

Jokes? Maybe I am, but at least I am having fun.

Now to be fair, I do admire one thing that Krenov does. He has found a way to make a living doing what he is passionate about. That is inspirational, so I guess I may have misspoke earlier. This sort of cult following of anybody, Krenov, Maloof, Abrahms, or whoever, is not healthy. You need to be able to step back and be objective.

The original intent of this subject is a valid comparison of air dried vs kiln. Krenov has created a lot of high profile test subjects.

Have a good day,

[Steve Rozmiarek]

Steve,

I have a lot more experience with kiln-dried than air-dried lumber because that's what's most available commercially, but in my somewhat limited experience, air-dried seems milder cutting and working. I don't know if it's always that way, or has to be that way due to something in the nature of kiln-drying (or hurried kiln-drying perhaps), but that's been my experience.


Frank, I wonder if the hurried kiln drying is the key? I'm making a project out of a pile of lumber that was an air dried walnut tree currently. I needed a bit more stock, so I pulled a couple kiln dried boards as well, and in this particular instance, the kiln dried is easier to hand plane. I have seen it the reverse though. Either way, wood is a variable medium. Have a good day,

[David Keller NC]

"Your opinions of Krenov are certainly your own and no business of mine. The point I was trying to make was that he worked with air-dried lumber and his pieces have not failed to my knowledge...in multiple and diverse locales around the world."

Actually, that was the point I was trying to make (admittedly a bit obtuse) - I have not seen any difference in failures, nor workability, between kiln-dried or air-dried wood pieces that I've made, Krenov's opinions of the two not withstanding.

[Steve Rozmiarek]

To all, I broke one of the unwritten rules of this site, and gave conflict a means to show its face here. As civility differentiates this forum from the others, I apologise for being confrontational. We all draw inspiration from different sources, and respect for the different views needs to be tolerated, and encouraged, to maintain an active and dynamic medium to express and test ideas. This would be a very boring place if we all where the same.

[Doug Miller 303]

I've been in construction now for 11 years, mostly remodeling houses. I've built hundreds of houses, worked on hundreds more, and seen more poor craftsmanship than one should be allowed. I've done rough framing work, and I've done finish carpentry work. I've built custom cabinets. I've worked in the eastern states and I've worked in the western states, each posing unique challenges. I've also got a degree in Architectural Engineering.

And I can tell you WITHOUT A DOUBT that kiln dried lumber will swell with humidity, and shrink with the lack thereof. I've seen it first hand. I've even seen plywood (supposedly stable) swell significantly.

In the western states, the MC can get down as low as 3% during the summer, but typically won't get above 8% in the winter. The eastern states pose more of a challenge. The MC there can get as high as 12 or 14% in the summer and drop down to about 6% in the winter. The drop in humidity in the winter combined with shrinkage at lower temperatures can make one's life interesting.

When one is working on a house, expansion and contraction issues have to be considered, reconsidered, and then reconsidered again. Always keep this in mind for each step of the process. (Yes, you are right to say that expansion and contraction are caused by many different factors.)

I built and installed a custom screen door out of kiln dried poplar during the winter of 2006-07 for a 100 year old Victorian home in NW Ohio. It has polished brass steeple hinges and a mortise lockset, but I digress. When the humidity of summer rolled around, the door wouldn't open. It had to literally be kicked open. I left a generous 1/8" gap all around the door when I installed it, knowing that it would swell come summer. And I had always been told that poplar was one of the more stable species.

Maybe there is some truth to the video, and there is probably somebody out there with a doctorate degree that can tell us.

However, I would like to ask:

1. Which species of wood was tested?

2. If only one or two species, then why wasn't a cross section of "typical" species chosen? Why not test engineered lumber products also?

3. Where were these tests performed? East or West? What kind of equipment was used to control the humidity and temperature? Was daylight a factor? Was wind a factor?

4. Were the test pieces finished or raw?

5. If finished, what type of finish or finishes? How many coats?

6. If raw, was it sanded smooth? If sanded, to what degree?

7. How often was the moisture tested? And how do different species compare? How do the different types of finishes compare? How do the different finish/species combinations compare?

8. Was the test piece measured for length, width and depth? How often?

9. What kind of testing equipment was used? When was it calibrated?

10. How often was the temp and humidity tested? Was the outdoor temp and humidity tested also? If so, was the difference added into the equation?

11. Was the change in temp/humidity done quickly or slowly? Or both?

12. How many times was the temp/humidity cycled? Did this have a factor in the MC content or amount of swell/shrinkage over the course of the test? What affect did cycling have on the different species and species/finish combinations?

13. Were various temp/humidity combinations tested?

Until we know the answer to all of these questions, then any tests that have been done are exactly that........a test. I for one will stick to what I've learned from experience, and I know that kiln dried lumber will shrink and swell.

Is anybody out there willing to take the time to do these tests?

Thank you,

Doug

[David Keller NC]

"Maybe there is some truth to the video, and there is probably somebody out there with a doctorate degree that can tell us."

I have a doctoral degree. There is no truth to the video.:)

[Cody Colston]

To all, I broke one of the unwritten rules of this site, and gave conflict a means to show its face here. As civility differentiates this forum from the others, I apologise for being confrontational. We all draw inspiration from different sources, and respect for the different views needs to be tolerated, and encouraged, to maintain an active and dynamic medium to express and test ideas. This would be a very boring place if we all where the same.


Hear, hear.

That is very big of you Steve. BTW, I didn't think you were confrontational, just highly opinionated. :D

[James Boster]

I will add a short reply here. I own a sawmill business and do kiln drying. The statement the OP is talking about is FALSE! If you want to keep kiln dried lumber "dry" it needs to be stored in a humidity controlled enviroment at about 35% humidity. Any more and it will pick up moisture, less it will give it up. The "expert" on this topic would be Dr Gene Wengert. If anyone wants to ask this question on woodwebs "sawing and drying" section I'm sure he will give you the same answer. How fast wood will pick up moisture varies by species and humidity. I have seen oak and cherry go from 6-8% to 12-14% in less than a month in August in central WV when the humidity is around 85-90%. Nuff said.

[Richard M. Wolfe]

With respect to comparing air dried to kiln dried, I don't know that the results would be valid. The wood from individual trees may vary enough to make differences in working. That is, air dried compared to other air dried may be different. Amount of variability probably depends on species. Being where I am (central Texas) I'm thinking of mesquite, and differences in trees can be marked. And I've had wood from different parts of the tree vary a lot. On and on.

[Andy Pratt]

I had no idea my question would generate this much interest, thank you all for your detailed replies. While there's no way I could hope to respond to everything mentioned here, I'll say that it was enlightening to read such a wide range of thoughts on the subject. If I can try to roll up the consensus of the various postings into a coherent thought I would probably settle on something along the lines of:

While kiln drying may slow the future rate of MC change in a wood (vs. air drying), it does not prevent, to any degree that has a major impact on furniture design, the wood from returning to an equilibrium MC based on the environment it is in.

I suppose the bottom line that we can all agree on is that you need to adjust for wood movement no matter what you do, so the point is mostly academic. I asked the original question partly to satisfy my curiousity but primarily to know what experienced people think so that I'm not suprised when a potential customer asks me why I use one over the other someday. Between reading both Hoadley books and this thread I definitely that I can speak intelligently on the subject and offer a wide range of thoughts now.

Thanks,
Andy

[Neal Clayton]

I've been in construction now for 11 years, mostly remodeling houses. I've built hundreds of houses, worked on hundreds more, and seen more poor craftsmanship than one should be allowed. I've done rough framing work, and I've done finish carpentry work. I've built custom cabinets. I've worked in the eastern states and I've worked in the western states, each posing unique challenges. I've also got a degree in Architectural Engineering.

And I can tell you WITHOUT A DOUBT that kiln dried lumber will swell with humidity, and shrink with the lack thereof. I've seen it first hand. I've even seen plywood (supposedly stable) swell significantly.

In the western states, the MC can get down as low as 3% during the summer, but typically won't get above 8% in the winter. The eastern states pose more of a challenge. The MC there can get as high as 12 or 14% in the summer and drop down to about 6% in the winter. The drop in humidity in the winter combined with shrinkage at lower temperatures can make one's life interesting.

When one is working on a house, expansion and contraction issues have to be considered, reconsidered, and then reconsidered again. Always keep this in mind for each step of the process. (Yes, you are right to say that expansion and contraction are caused by many different factors.)

I built and installed a custom screen door out of kiln dried poplar during the winter of 2006-07 for a 100 year old Victorian home in NW Ohio. It has polished brass steeple hinges and a mortise lockset, but I digress. When the humidity of summer rolled around, the door wouldn't open. It had to literally be kicked open. I left a generous 1/8" gap all around the door when I installed it, knowing that it would swell come summer. And I had always been told that poplar was one of the more stable species.



i've learned all of these lessons myself as well over my short time of building windows and doors.

and the answer to when the wood will stop moving posted earlier, if ever, is in fact, never. the original century+ old windows and doors i have are still snug in the summer and loose in the winter, however they are operable year round, that's the only thing i can feasibly accomplish with the ones i build, imo.

the best i've found that i can do is consider the time of the year you're building something when accounting for movement tolerances. a door built with 1/8 of tolerance in the summer will shrink too much in the winter. a door built with 1/8 of tolerance in the winter will swell too much in the summer.

using traditional means of sealing said doors/windows (parting beads and spring bronze weather stripping) alleviates some of these problems by allowing for more movement tolerance while maintaining a barrier to the outside, but not all.