Conditioning lumber -- The final step in drying

      Why conditioning is the last but crucial step in the drying process. December 12, 2000

What is meant by “conditioning” at the end of the drying cycle? Is it needed with a dehumidifier kiln?

Forum Responses
Conditioning is the process of removing drying stresses that were created in the early stages of drying when the shell tried to shrink, but the wet core prevented such shrinkage. In conditioning, the shell has moisture added to it quickly, so that the shell tries to swell but the dry core prevents it. The net effect is that the attempted swelling cancels the attempted shrinking. Lumber without adequate stress relief is called "casehardened." Such lumber will pinch the saw when ripping and will have immediate warp when machining.

Conditioning is needed for all products that require no or minimal stress. Air dried lumber has minimal stress already so little conditioning is required. DH has no special key on eliminating stress, however.

Gene Wengert, forum technical advisor

I am also looking at building a DH kiln for my green lumber using a Nyle DH200 unit. I am unsure what is the best way to dry my green lumber to insure a quality product for customers. Gene, are you saying that DH kilns are not the best way to dry green wood quickly and get repeatedly excellent results?

"Are you saying that DH kilns are not the best way to dry green wood quickly and get repeatedly excellent results?"

NO. DH kilns are (as many drying techniques) excellent. However, without adequate stress relief (conditioning or casehardening relief), the lumber may not be suitable for all users. You can use steam in the DH kiln (remove the unit from the system by blocking it out so you do not steam the DH unit); some people have tried water spray (SII Mystifier), but I have not heard from a DH user about this.

All drying systems drying from green create drying stresses (casehardening)--it is a natural event. The amount varies from system to system, depending on the speed of drying, mainly (faster is more) and the temperature used (lower is less).

Gene Wengert, forum technical advisor

Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?

Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: Primary Processing

  • KnowledgeBase: Primary Processing: Air Drying Lumber

  • KnowledgeBase: Primary Processing: Kiln Operation

  • KnowledgeBase: Knowledge Base

    Would you like to add information to this article? ... Click Here

    If you have a question regarding a Knowledge Base article, your best chance at uncovering an answer is to search the entire Knowledge Base for related articles or to post your question at the appropriate WOODWEB Forum. Before posting your message, be sure to
    review our Forum Guidelines.

    Questions entered in the Knowledge Base Article comment form will not generate responses! A list of WOODWEB Forums can be found at WOODWEB's Site Map.

    When you post your question at the Forum, be sure to include references to the Knowledge Base article that inspired your question. The more information you provide with your question, the better your chances are of receiving responses.

    Return to beginning of article.

    Refer a Friend || Read This Important Information || Site Map || Privacy Policy || Site User Agreement

    Letters, questions or comments? E-Mail us and let us know what you think. Be sure to review our Frequently Asked Questions page.

    Contact us to discuss advertising or to report problems with this site.

    To report a problem, send an e-mail to our Webmaster

    Copyright © 1996-2019 - WOODWEB ® Inc.
    All rights reserved. No part of this publication may be reproduced in any manner without permission of the Editor.
    Review WOODWEB's Copyright Policy.

    The editors, writers, and staff at WOODWEB try to promote safe practices. What is safe for one woodworker under certain conditions may not be safe for others in different circumstances. Readers should undertake the use of materials and methods discussed at WOODWEB after considerate evaluation, and at their own risk.

    WOODWEB, Inc.
    335 Bedell Road
    Montrose, PA 18801

    Contact WOODWEB

  • WOODWEB - the leading resource for professional woodworkers

      Home » Knowledge Base » Knowledge Base Article