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Thread: heat treating walnut (and other species)

  1. #1

    heat treating walnut (and other species)

    I have a lot of air-dried lumber (white and red oak, cherry, walnut, ironwood, ash...), some of which shows some bug activity at some point.
    There is a local kiln that will do custom work, and could do the heat treating necessary to kill any potential pests.

    My question is this - I love the look of air-dried walnut with the different colors in the grain. I understand that kiln drying will mute that variation in the walnut and give it much more of a uniform appearance. Will heat treating the walnut lumber to a high enough temperature to kill any pests (135-140F) result in that aforementioned dulling of the grain variation, or is that only a problem if you have the lumber dried in the kiln, not just heat treated? I want to eliminate any bugs, but don't want to loose the wonderful grain!

    Thanks!
    Matthew

  2. #2
    Steaming is well known (and intentionally used) to reduce the color variation in walnut. I don't believe that normal kiln drying has that effect.

  3. #3
    Join Date
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    No worries as long as they don't use steam as Kevin mentions. It's the steaming that's purposely done to walnut to increase yields that does the majority of the color change that's often associated with kiln dried black walnut. That tends to darken the sapwood and lighten the heartwood to the same ruddy brown, rather than retaining the rich ambers, purples, greens and browns of the unadulterated black walnut timber.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  4. #4
    Jim and Kevin, Thank you.
    And just curious now - are there any other species that you need to be careful with when kiln drying so you don't alter the appearance?

  5. #5
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    I would have to defer to the actual lumber making folks here on that question. I would imagine there are other species that might be reactive to steam treating but have never personally experienced such a major difference as comparing the air dried walnut I've had produced from my own property to what I've seen at hardwood suppliers. The steam may also be used to help control other factors, too. I don't know enough about it to be sure of the details.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  6. #6
    I wouldn’t worry about bugs in walnut if all the sapwood is removed. Walnut has been used for out-buildings and such because of its
    formerly known to people resistance to being eaten. The bugs still remember. I see nothing wrong or risky in using air dried walnut. The
    modern insistence on kiln drying comes from spec writers.

  7. #7
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    Hi Matthew, I'm a kiln operator. A couple of comments.

    First, as Jim and Kevin previously mentioned, the only type of kiln that will change the color of walnut is one that dries with steam, called a "conventional kiln" in our industry. The other three types of wood kilns are dehumidification, vacuum (both shallow and deep versions which dry differently), and solar.

    Steam kilns utilize two different types of steam - wet and dry. Wet steam is the one that will alter the color on BW.

    Years ago I did an experiment where I cut a board in two, and air dried one section and kiln dried the other in a commercial dehumidification kiln. Afterward I would challenge people to identify which one was which, and to explain why. Nobody could, because the two boards looked identical.

    Regarding bug activity, Mel brings up a good point. In general black walnut is toxic to bugs, due to the juglone that it contains. Having said that, I have personally seen termite colonies present in green black walnut slabs, as well as lyctid powder post beetle activity in the sapwood. Bottom line, if there are signs of an active infestation in your BW, it would be a good idea to have them sterilized along with the rest of your lumber.

    BW that has been air dried and kept separate from other species, and does not exhibit any bug activity, can usually be safely used w/o kiln sterilization.

  8. #8
    Scott, what temperature and for how long do you consider necessary for killing off insect infestations? If insect holes are observed without new frass evident does that require heat treatment?

  9. #9
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    Quote Originally Posted by Kevin Jenness View Post
    Scott, what temperature and for how long do you consider necessary for killing off insect infestations? If insect holes are observed without new frass evident does that require heat treatment?
    USDA specs call for heating all portions of the lumber to 133F or higher in order to properly sterilize it. Some kilns, such as a conventional kiln drying pine, dry at temps higher than 133 so no additional sterilization cycle is required. However, vacuum and DH kilns usually dry at temps below 120F, so the sterilization cycle is a separate cycle at the end. Most kiln operators will crank the heat up to 155F or so and leave it there for 12 hours in order to sterilize at the end of the run. Since they only need a 13 degree temp rise in the wood (From 120 to 133), the 12 hours is adequate for most species and thicknesses. For really thick beams, we will run a 48 hour or longer cycle.

    In hardwoods, the most concerning pests are lyctid powder post beetles and dry wood termites. They will stay in dry lumber. Ambrosia powder post beetles leave on their own when the wood is dry. So re the insect holes, it really depends upon what made the holes. If in doubt, it's a good idea to sterilize.

  10. #10
    Join Date
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    Black Locust can be heat treated to look like Ebony. It is a trick banjo makers use. I have had some success and am trying to come up with a reliable recipe. This image shows a two ply fretboard the top layer is Walnut the bottom layer is toasted Black Locust. The neck is maple with the old stain and varnish partly scraped off.
    IMG_0279 (2).jpg

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