Question on wood drying

[Craig D Peltier]

My question is when wood is cut into boards, and if it goes into a kiln right away do the ends still need to be sealed? When they come out should they be sealed? I understand air drying you need to.

Thanks

[Howard Acheson]

Ends should always be sealed with hours of being cut to length. With some woods immediate sealing is more important like maples and oaks. Once you've missed the 10-12 hour window sealing is no longer going to work well and you may just have to deal with any resulting end checking.

[Craig D Peltier]

Thanks Howard, appreciated.

[Kevin Bourque]

We always let our lumber air dry for at least 6 months before kiln drying it.
Putting fresh cut wood immediately into a kiln is a sure fire way to get cupped, twisted, and badly checked wood.

That said, I have no idea if sealing green wood before kiln drying will have much of an affect on the finished product.

[Tom Fischer]

I think it helps if you fell and mill the lumber when it is below Freezing.
MHO

[Kevin Bourque]

I think it helps if you fell and mill the lumber when it is below Freezing.
MHO

Well it certainly helps if you cut & stack the wood when its cooler rather than hotter outside. The slower the drying the better, in my experience.

[Scott T Smith]

Putting fresh cut wood immediately into a kiln is a sure fire way to get cupped, twisted, and badly checked wood.




Kevin, whenever this is the result of drying wood in a kiln it is because the kiln was not properly set for the species, thickness and moisture content of the wood being dried. It is a clear idicator that kiln operator attempted to dry the wood at a rate significantly in excess of it's safe drying rate.

In a perfect world, for minimum wood degrade the tree would be felled and end sealed on day 1, milled on day 2, and the boards placed into the kiln on day 3.

If you want to learn more about the drying process, please take a few minutes to read a post that I made a while back. Start with response #6 on this thread:

http://www.sawmillcreek.org/showthre...ught-yesterday (http://www.sawmillcreek.org/showthread.php?180522-Air-drying-vs-kiln-this-wood-I-bought-yesterday)

That will help provide you with some background on drying wood.

If you want to learn more about drying lumber, one of the best places to start is with the USDA Forest Products Labratory manual that Gene Wengert and Joe Denig wrote in 2000. Here is a link to it:

http://www.arconlab.com/handyman/woo...0Hardwoods.pdf (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.

In actuality, proper kiln drying offers the kiln operator the best control over the entire drying process - something that cannot be achieved by air drying.

Certain species/thicknesses, such as 12/4 oak, etc, are air dried first for economic - rather than quality reasons. When drying thick boards/planks from slow-drying species, the amount of economic loss due to degrade resulting from uncontrolled air drying this wood is less than the cost to run the kiln for 4 months at the low rate needed to properly dry them w/o degrade. Hence air drying is preferred in these instances for economic reasons - not quality reasons.

Most degrade that is a result of the drying process occurs between the time that the boards are milled and when they dry down to 35% MC. Almost always, this degrade is due to the wood being dried too aggressively. A properly managed kiln cycle allows the operator to closely control the drying process; often times we are slowing the rate of drying down as opposed to trying to speed it up.



Craig, in answer to your questions, if you want to minimize degrade and maximize yield on hardwoods you need to end seal logs/boards - irrespective of whether they are air or kiln dried.

During the drying process, we are trying to remove water from the face of the boards - not the ends - and end sealer helps to minimize the amount of moisture loss (and resulting degrade) from the ends of the boards. This impact is the same for KD or AD wood.

If you can't end seal them right away, consider trimming an inch or two off of the boards (to get rid of any checks that have already started) and apply fresh end sealer. End checks in boards are similar to cracks in glass - once they get started they tend to keep growing. The key thing is to prevent them from getting started in the first place. Baileys end sealer (shipped from California) and Anchor Seal Classic are two that have a great reputation in the industry.

Typically the end sealer will evaporate off of the end of the boards when they go through the sterilization cycle at the end of the kiln run. Thus you can use boards that have been end sealed just about all of the way to the end of the board (within 1/2" or less).

Occasionally the log will have internal stresses in it, and end sealer won't prevent checks from occurring that are related to excessive tension or compression wood cells. However, it will minimize normal drying degrade.

[Scott T Smith]

I think it helps if you fell and mill the lumber when it is below Freezing.
MHO

Actually, it doesn't.

The rate of drying is determined by temperature and relative humidity. Cooler temps result in slower drying rates, which in general is more forgiving for the lumber and results in less degrade. When wood is frozen, it is not drying at all, so being frozen does not help the drying process.

Cooler temps (50 degree range) is good - frozen is not.

[Chris Fournier]

It is advantageous to cut trees in the winter as the moisture content in the standing tree is lower, staining is less prevalant and moving in the bush is easier. Drying lumber in the winter is slower as Scott points out. Conventional kilns are expensive to run and consequently cost $$$. The drier the lumber going into the kiln, the less kiln time, the less money. Learning to air dry most NA species properly is easy and inexpensive. It does however require a lot of handling from sawn to dry lumber.

[Keith Outten]

There is an exception to the rule.
If you are drying wood in a dehumidification Kiln such as an EBAC machine and you put the lumber in the kiln immediately you don't ever need to seal the ends no matter what the species. I ran an EBAC kiln for ten years, my goal was to dry the absolute best quality lumber. Once lumber is sealed inside a kiln you then have total control over the process. A dehumidification kiln uses very little heat, it simply removes the moisture in the air inside the kiln and when the moisture in the kiln is less than the moisture in the wood it will give up its water content.

A very slow 4/4 drying schedule in an EBAC kiln takes about 6 weeks but its worth every minute. The quality is incredible with no checking, cupping, discoloration or any interior stress.
.

[Cody Colston]

It is advantageous to cut trees in the winter as the moisture content in the standing tree is lower, staining is less prevalant and moving in the bush is easier.

Actually, for most species, the moisture content is slightly higher in winter than in summer but it changes less than 2% year-round in all species. Moisture is more fluid in the warmer months. I do agree that staining is less prevalent because the fungi that cause staining prefer temps around 80 degrees for growth. It's also definitely easier to move around in the woods during the winter.

For small-time wood harvesting, I don't think end-sealing the logs is a big deal. Yes, there will be some degrade from end-checks but not that much as a percentage of the total. For a big yard drying several hundred thousand board feet of lumber, that small percentage lost per board would add up to serious loss but not so much if drying a couple or three hundred board feet. I've quit end-sealing my logs as there are always some end checks anyway and the little bit of lumber saved is not that much per load in my solar kiln (400 bft capacity).

[Scott T Smith]

Actually, for most species, the moisture content is slightly higher in winter than in summer but it changes less than 2% year-round in all species. Moisture is more fluid in the warmer months. I do agree that staining is less prevalent because the fungi that cause staining prefer temps around 80 degrees for growth. It's also definitely easier to move around in the woods during the winter.



+1. Logs weigh basically the same irrespective of whether they are cut in the summer or the winter, which means that the IMC% (Initial Moisture Content) is the same or close. I concur with both Chris and Cody re the staining and moving.


There is an exception to the rule.
If you are drying wood in a dehumidification Kiln such as an EBAC machine and you put the lumber in the kiln immediately you don't ever need to seal the ends no matter what the species. I ran an EBAC kiln for ten years, my goal was to dry the absolute best quality lumber. Once lumber is sealed inside a kiln you then have total control over the process. A dehumidification kiln uses very little heat, it simply removes the moisture in the air inside the kiln and when the moisture in the kiln is less than the moisture in the wood it will give up its water content.

A very slow 4/4 drying schedule in an EBAC kiln takes about 6 weeks but its worth every minute. The quality is incredible with no checking, cupping, discoloration or any interior stress.
.



Keith, I'm glad to hear about your Ebac experiences. I've been very pleased with my Nyle DH kiln, which operates on similar principles and with similar results. It has been my experience that lumber dried in a DH kiln works similar to air dried lumber, as opposed to lumber dried in a conventional kiln when tends to be more brittle.

The reason that I am a proponent for end sealing is because checks can begin within a few hours of the tree being felled and the logs bucked to length. I try to end seal the logs right after felling (usually before they are loaded onto my trailer), as it usually takes a few days to mill up an entire load for the kiln, and during this time checks will start occuring if the logs are not sealed.

[Chris Fournier]

Actually, for most species, the moisture content is slightly higher in winter than in summer but it changes less than 2% year-round in all species. Moisture is more fluid in the warmer months. I do agree that staining is less prevalent because the fungi that cause staining prefer temps around 80 degrees for growth. It's also definitely easier to move around in the woods during the winter.

For small-time wood harvesting, I don't think end-sealing the logs is a big deal. Yes, there will be some degrade from end-checks but not that much as a percentage of the total. For a big yard drying several hundred thousand board feet of lumber, that small percentage lost per board would add up to serious loss but not so much if drying a couple or three hundred board feet. I've quit end-sealing my logs as there are always some end checks anyway and the little bit of lumber saved is not that much per load in my solar kiln (400 bft capacity).

Perhaps my methods or equipment were not precise enough when I looked into this. I used to buy a half dozen hard and soft maple logs a year for a good while. I always found that the winter cut logs had 3% to 5% less MC. I used a moisture meter and the weight wet/dry method to establish MC. I also was very careful about the sample temperature when using the meter. I have some reading to do...

[Scott T Smith]

Perhaps my methods or equipment were not precise enough when I looked into this. I used to buy a half dozen hard and soft maple logs a year for a good while. I always found that the winter cut logs had 3% to 5% less MC. I used a moisture meter and the weight wet/dry method to establish MC. I also was very careful about the sample temperature when using the meter. I have some reading to do...


Chris, moisture meters are notoriously inaccurate above the fiber saturation point of wood. Additionally, temperature impacts the reading. My Delmhorst meters require me to input the temp along with the species for a more accurate reading; but even that is only accurate below the FSP.

[Tom Fischer]

Last couple of trees I took (500 bf, black walnut), I didn't get all the boards picked up until the next day.
The high temps were about 20 degrees F.
No drying started until everything was properly stickered.
The 4/4" stuff dried almost perfect. And didn't use any Anchorseal.
Just saying.