Air drying vs kiln this wood I bought yesterday

[Joe Cowan]

I bought some quartersawn sycamore in 9/4 thickness, up to 15" wide and varying lengths. It must of had squirrels running around its branches last week. After talking to the sawmill guy and telling him my options of storing/drying this wood, we decided that I put it up on sticks in my 5' high crawlspace at my house. The crawlspace backs up against a basement wall, and is usually cool year round. It has a concrete floor and vents. He suggests I put a fan on it from the side and keep and gentle breeze blowing through it. A good friend of mine thinks I am crazy as it should be kiln dried or I will lose wood due to checking. I tend to think I will be ok. Any opinions?

[Todd Burch]

That stuff is going to take a few years to season. You gonna keep a fan on it got 2+ years? I think not.

Cool doesn't mean anything when air drying wood, although cool would certainly be preferred over 100 degree sun straight on.

Accessible to natural breezes, well covered, rain and sprinklers kept away, and you'll be fine. If you are in a hurry to use all of it, I would suggest finding a kiln operator versed in drying thick hardwoods. Kiln operators hate thick hardwoods - they take a long time to dry in their kilns.

Todd

[Don Buck]

What is the desired look and application of your 9/4 sycamore? If you want blue stained and spaulted wood you might have a good plan. If you want bright stock you will be dissapointed. A crawl space has to be one of the worse places to try to dry wood. Most homeowners close their vents in the winter and open them in the warmer months. Even with a fan running you are not going to get the required air exchange in the closed environment (vents closed) and in the warmer months with the vents open you will be bringing in high moisture laden air into a cooler environment which will actually raise the relitive humidity in the crawlspace.
Sycamore stains very quickly, if you want bright stock the best prescription is to get the stock into a dry kiln as soon as possible. If you want to air dry the lumber put it outside on a good level bottom (cinder blocks with 4 x 4's on top will work) and get the lumber on sticks (24" centers is okay for 9/4). Cover the top with a water resistant top but do not restrict the air flow through the pile. Even with proper air drying, my experience is you will still get a high percentage of stain in sycamore. To get bright stock sycamore needs an experienced kiln operator utilizing a kiln schedule with the proper combination of air flow, humidity and temperature.

[Joe Cowan]

I will not need it until 2 years. I was planning on putting a fan on it for the first month or so to get some of the rapid water loss away from the wood, but not for 2 years. The guy at the mill told me he did not get over 90 degrees for the first week in the kiln as he wanted to get a slow start on pulling the water out of the wood. We both agreed that my crawlspace would be as good as I could do as the temp were fairly stable and not a big swing of temps in shorter periods of time.

[Howard Acheson]

I you live in an area subject to mold in crawl spaces, you are going to have big problems. A lot of water is released during the initial drying of wood.

First, the ends of the boards should be immediately coated with a proper end seal material. Anchorseal is the best. Tar can be used but stay away from any type of paint. Paint will not prevent moisture penetration. If you can't get the ends sealed within a few days of cutting, the damage will already have occurred.

As said, the wood should be stacked and stickerred. Find a location where the wind will move through the stack. Make the first course 10-12 inches off a tarp covered ground area. Cover the stack with plywood or better, corrugated fiberglass privacy material. Do not cover the sides as air must be able to freely move through the stack.

[Joe Cowan]

I you live in an area subject to mold in crawl spaces, you are going to have big problems. A lot of water is released during the initial drying of wood.

First, the ends of the boards should be immediately coated with a proper end seal material. Anchorseal is the best. Tar can be used but stay away from any type of paint. Paint will not prevent moisture penetration. If you can't get the ends sealed within a few days of cutting, the damage will already have occurred.

As said, the wood should be stacked and stickerred. Find a location where the wind will move through the stack. Make the first course 10-12 inches off a tarp covered ground area. Cover the stack with plywood or better, corrugated fiberglass privacy material. Do not cover the sides as air must be able to freely move through the stack.


We coated the ends with anchorseal. I have access to a kiln, but wanted air dry as I think the color is better. But not at the expense of checks, mold etc.

[Scott T Smith]

Joe, wood dries based upon a blend of three environmental factors, and they are 1 – temperature, 2 – relative humidity, and 3 – air flow.
Drying rate is increased with (a) hotter temperatures, (b) lower RH%, and (c) faster air speeds. Temperature and RH% have a greater impact than air speed.
Each species of wood has a maximum safe daily drying rate, and this rate varies based upon three factors: 1 – the species of wood, 2 – the thickness of the wood, and 3 – the moisture content of the wood. The maximum safe daily drying rate can be safely increased as wood becomes progressively more dry.

In general, you can divide the drying process into three stages. These are 1 – from green down to 35% moisture content, 2- from 35% MC down to 25% MC, and 3 – from 25% MC down to final MC (typically 6% - 8% for indoor projects and 14% or so for outdoor projects or framing lumber).

Drying related degrade (damage) can be loosely divided into two categories – physical and aesthetic.

Most drying-related physical damage to lumber occurs between the time that it is milled and when it reaches 35% MC. This is the most critical stage of drying, and during this time surface checking will occur if the wood is dried too quickly (checking does not occur when wood is dried too slowly) and internal checking (honeycomb) will occur if the drying speed is so excessive that surface hardening occurs. Often times, these checks don’t become visible to the naked eye until the wood has dried below 25%MC, even though they occurred when the wood was at a higher MC%. They key to preventing physical damage is to 1 – end seal the lumber and 2 – don’t dry it too quickly.

Most drying related aesthetic damage also occurs during the stage of green down to 35% MC, and this is usually due to being dried at too slow of a rate. One thing to keep in mind is that aesthetic damage (such as mold or other discoloration) usually requires a temperature between 70 - 100 degrees to occur; if the wood is kept less than 50 – 60 degrees, the potential for aesthetic damage is minimized. So, the key to minimizing aesthetic damage is to make sure that the wood is actually drying instead of being so moist that it is remaining static, and to keep it cool.

There is another minor impact, and that is that wood that is quartersawn takes about 20% longer to dry than flat sawn wood.

One of the reasons that many experienced people who air dry like to harvest and mill their lumber in the fall and winter is because the cooler temperatures typically prevent the occurance of aesthetic degrade, and by the time that summer arrives and the temperature rises, the wood has dried enough so that the surface MC% is below that required for the degrade to occur.

The ratio of safe drying rate based upon changes in board thickness is exponential. Drying rates are typically listed for 4/4 lumber, with 8/4 lumber having a safe drying rate being around .4 of the rate of 4/4.

Here are some maximum 4/4 [8/4 is in ()] daily drying rates for typical hardwood species:

Ash – white: 5% (2%)
Basswood – 12% (4.8%)
Beech – 5% (2%)
Birch - 5% (2%)
Cherry – 7% (2.8%)
Maple (soft) – 7% (2.8%)
Maple (hard) – 5% (2%)
Oak- Red upland – 3.8% (1.5%)
Oak – white upland – 2.5% (1%)
Oak – southern Red – 2% (.8%)
Sycamore – 3.8% (1.3%)
Walnut – 8% (3.2%)
Poplar – 15%. (6%)

Above we have the list of what the drying rates that you want to try to achieve, so how do you do that? The answer is by controlling the temperature, RH% and air flow to stay within a safe range for the species, thickness and MC% of your wood.

Here are three different environments that provide roughly the same safe drying rate (3% give or take) for a typicaly 4/4 oak or sycamore board. This is a good rate to target from green down to 25%MC

55 degrees, 44% - 65% RH (or less)
75 degrees, 74% - 82% RH
90 degrees, 85% RH
105 degrees, 93% RH

For 8/4 oak and sycamore lumber, the numbers change significantly. Here are some good targeted numbers for green down to 25%MC

55 degrees, 76% - 88% RH
75 degrees, 91% RH
90 degrees, 92% RH

When comparing your crawl space versus your workshop, simply compare the average temp and RH ranges to determine the impact to your lumber. If your workshop is similar to most, it is probably around 70 degrees and 50% RH. In that environment, 8/4 oak or sycamore would most likely be severely damaged, as its drying rate index would be approximately 400% greater than the target. This damage would be characterized by excessive surface checking. In the crawl space though, most likely you will fall in or near the 55 degree, 75 – 88% RH target. To minimize the potential for mold to occur, simply keep the air moving and within the targeted RH% range.

Now, let’s talk about time. There is an “Old wives tale” amongst woodworkers that lumber requires “1 year per inch of thickness to air dry”. Knowledgeable professionals have been trying to “kill” this rule for a long time, as it simply isn’t accurate with today’s understanding of how and why wood dries, as well as equipment that is available to measure MC%.

If you stack and sticker your 9/4 sycamore lumber in a crawl space that is approximately 55 degrees and 80% RH with a gentle fan running across it, in approximately 90 days your lumber should be between 20% - 27% MC%, give or take. At that time, once it is below 25%MC it will be safe to move it into an environment where it can dry at a faster rate, such as your workshop or some type of storage shed.

Best of success to you on your project and in this new area (drying) of your woodworking journey.

Scott

[John TenEyck]

Scott, thanks for the great education. I learned a lot, and it filled in some gaps in my understanding. Much appreciated.

[Scott T Smith]

Scott, thanks for the great education. I learned a lot, and it filled in some gaps in my understanding. Much appreciated.

John, glad to help.

SS

[Nelson Howe]

Scott,
That was some great, quite specific information. Obviously it is essential knowledge for you. Can you reference any documents where the rest of us can access this information? I've got some some red oak, hard maple, cherry and ash at different stages of air drying, and would love to know more about what I'm doing with it.

Thanks,

Nelson

[Jim Becker]

Air drying should be done out in the open where prevailing winds can help wick off the moisture as it leaves the wood. You'll also want it with a sloped cover on top to keep standing water off as well as a bit of weight to help keep things flat while it's drying, especially with sycamore, even though it's QS.

[Ken Mosley]

You've recieved a thorough education on sycamore already and I can only add from my experience: Sycamore NEVER stops moving regardless of it's drying method. Be sure to keep that movement in mind as you plan your use of it. It is gorgeous wood with unbelievable grain configurations and if you control and allow for it's "mood moves" you'll get some spectacular results. I used some kiln dryed sycamore for library shelving and had to replace them. Good luck

[Scott T Smith]

Scott,
That was some great, quite specific information. Obviously it is essential knowledge for you. Can you reference any documents where the rest of us can access this information? I've got some some red oak, hard maple, cherry and ash at different stages of air drying, and would love to know more about what I'm doing with it.

Thanks,

Nelson

Nelson, three of the most knowlegeable experts in the US regarding drying lumber are Eugene Wengert (Gene), Joe Denig, and Don Lewis. I've met all three, and taken classes from Joe and Don, and their knowledge is formidable. There is a plethora of information available on the internet from them that a name search will turn up.

Having said that, one of the best places to start learning more about drying lumber is with the USDA Forest Products Labratory manual that Gene and Joe wrote in 2000. Here is a link to it:

http://www.arconlab.com/handyman/wood/Drying%20Hardwoods.pdf


Another great resource is the older air drying manual from the USDA FPL, number FPL-GTR-117. This used to be available for downloading; now I think that you have to search further to find it. The manual that Gene and Joe wrote in 2000 is essentially an update of the -117 manual.

There is no one, single "correct" answer regarding air drying, as it depends upon the species, thickness, moisture content of the wood (which changes as it dries) and the external environment (temperature and RH%). As an example, in my portion of North Carolina you can successfully air dry just about any species of 8/4 lumber outdoors if you mill and start the process in the fall or winter. If you start air-drying 8/4 oak or sycamore in the hot summer months though, you will probably have some surface checking. On the other hand, 8/4 pine and cypress will air dry just fine year round.

In my brother's home town of Phoenix, AZ, if you attempt to air dry 8/4 oak or sycamore outdoors in the summer, you'll end up with a lot of firewood (and most likely in the winter too)!

Regards,

Scott

[James White]

Scott,

That was a very generous response. It will serve so many here. So thank you!

I was wondering if you knew where I could find more information regarding kiln schedules for dehumidification kilns. Most of the literature is written with large scale production conventional kilns in mind. I have a small self built dehumidification kiln and I find it hard to find information specific to this type of drying.

James

[Nelson Howe]

Thank you, Scott. I'll download the manual now.

Nelson

[Scott T Smith]

Scott,

That was a very generous response. It will serve so many here. So thank you!

I was wondering if you knew where I could find more information regarding kiln schedules for dehumidification kilns. Most of the literature is written with large scale production conventional kilns in mind. I have a small self built dehumidification kiln and I find it hard to find information specific to this type of drying.

James

Nyle Corporation has a lot of good info, but I don't see it available in the public domain.

If you'll send me an e-mail with your species and board thickness info, I can respond with specific recommendations.

[James White]

Thank you for the offer. I will likely take you up on that.

Speaking of air drying. I just came in from moving a stack of air dried oak. It was cut two winter ago and stickered to air dry. Well to my surprise. It all has a lot of surface checking. I don't know how deep it goes. But I think a very large percentage of it is ruined. I recall after the winter thaw he had some dry mild weather. Ill bet it happened then. This was my first batch of air dryed material. So far I have only went strait to the kiln and that work out very well. Now I am nervous about air drying. I guess it was just bad luck.

James

[Scott T Smith]

Thank you for the offer. I will likely take you up on that.

Speaking of air drying. I just came in from moving a stack of air dried oak. It was cut two winter ago and stickered to air dry. Well to my surprise. It all has a lot of surface checking. I don't know how deep it goes. But I think a very large percentage of it is ruined. I recall after the winter thaw he had some dry mild weather. Ill bet it happened then. This was my first batch of air dryed material. So far I have only went strait to the kiln and that work out very well. Now I am nervous about air drying. I guess it was just bad luck.

James
Not bad luck; but sometimes bad advice ;)

Oak is one of the more difficult species to dry w/o defects, especially thick oak (8/4 and greater). Usually winter drying is very forgiving, but it's always a good idea to understand the impact of temperature and RH%, monitor it accordingly so that you can adjust the environment if needed during the drying process.

Additionally, surface checking can occur if the wood is rewetted and redried throughout the drying process.

For a lot of hobbyists, if you buy wood green from the mill, dry it yourself, and lose 30% because of drying related degrade, it's no big deal because you still probably saved a lot of money on your lumber. But for a professional, every percent of degrade equates significant loss of revenue, and it is worthwhile to understand and manage the process.

[James White]

Additionally, surface checking can occur if the wood is rewetted and redried throughout the drying process.



Ah! You may have nailed the problem. A few months back I had discovered that the pvc? corrugated roof panels had bent in such a way. That water was flowing back into the overlapped section and on to the boards. That water cascaded and re-wet a majority of the stack by trickling down. Darn it!

I better check on my cherry and 8/4 oak!

Thanks a bunch,
James

[Joe Cowan]

I thought I would update everyone with the results of air drying this wood under my house in a very tall crawlspace. I took the wood out of the crawlspace about one month ago and stacked it in my shop on stickers. It felt dry and ready to use, but decided to take a piece of it to Scott Smith and let him use his fancy moisture meter to tell me if it was ready. It measured at 7.5% moisture content and has only very minor surface mold in a few spots. I only had a fan on it for the first couple of weeks and when it died, I just left the wood alone and let it do its thing. I did restack the pile once, and put the 2X12's on top of the stack standing up on its edge. All in all, I am very pleased with the results and will wait until next fall to start work on my next Maloof style rocker.

[Joe Cowan]

One other note, there was zero checking. We did spray the wax on each end of the boards prior to me bringing it home from Scott's mill.

[Jim Matthews]

This is a very interesting thread. There are few that show the real time delays, when buying rough lumber.

Will this rocker require steam bending?
I'm unclear how well Sycamore bends...

[Joe Cowan]

No steam bending. I have made one rocker out of walnut. I made up some forms and cut 3/16" strips and laminated both the rockers and the spindles. On the sycamore rocker, I plan of cutting the spindles out of solid wood and then shaping them by the patterns I have to fit.

[Carl Beckett]

This is a very interesting thread. There are few that show the real time delays, when buying rough lumber.

Will this rocker require steam bending?
I'm unclear how well Sycamore bends...

The trick is to just have lots of different piles lying around..... then you always have something ready to build with. (it takes up some SPACE!)

[Mel Fulks]

If you decide to get it kiln dried,I have a suggestion. Cut an end just a few inches long off a wide piece and put it where you can find it later. Before kiln drying the other piece ,mark it. After drying cut another short piece off . A KD sample and
an AD sample will allow some tests for the permanent effects of kiln drying, by periodically soaking in water and drying and recording changing widths.

[joe milana]

Interesting comment about Sycamore "never stops moving". I can get rough QS Sycamore pretty cheap & was thinking about using it for kitchen drawer boxes. Is the movement that bad that it would be a bad choice? :confused:

[Scott T Smith]

Interesting comment about Sycamore "never stops moving". I can get rough QS Sycamore pretty cheap & was thinking about using it for kitchen drawer boxes. Is the movement that bad that it would be a bad choice? :confused:


Personally, I would not hesitate to use QS sycamore for drawer boxes.

[Danny Hamsley]

Flatsawn sycamore can be a challenge to keep straight when drying. Quartersawn is definitely the way to go with sycamore.

[Cody Colston]

Scott, that as a very good, brief treatise on drying hardwood lumber...factual and precise. I'm also glad to see that you are trying to debunk the one-year-per-inch air drying malarkey although that particular myth gets quoted so much on woodworking forums that I doubt it will ever truly die. There is so much free, reliable, published data available on drying hardwood lumber that I'm continually amazed at the misinformation that gets repeated.

[Alan Schaffter]

Interesting comment about Sycamore "never stops moving". I can get rough QS Sycamore pretty cheap & was thinking about using it for kitchen drawer boxes. Is the movement that bad that it would be a bad choice? :confused:

I don't know if it still does, but the high end casework sold by Hardwood Artisans (http://www.hardwoodartisans.com/) in N. VA use to come with beautiful drawers made from QS Sycamore.

I think that load of Sycamore probably has some MAJOR flaws. You should NOT use it, you are wasting time and energy. Just so it is not a complete loss, I would be more than willing to drive down and get all of it out of your way!

Oh, by the way the info doesn't get any better than what comes from Scott S. and Gene Wengert!

[Philip Duffy]

Wow, what a great lesson for all of us on the wood drying process. Thanks, Scott! Philip