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Moisture transfer in humid climes
Do tropical and sub-tropical species re-absorb moisture when left in their humid, native lands? September 6, 2000
Q.
If wood is cut in a humid tropical enviroment and kiln dried (KD) there, will the dried lumber regain significant moisture if left in that high-humidity environment? If it does take on moisture, how much as a rule? And will that moisture come out once the lumber is delivered to a lower-humidity enviroment? How long for the moisture content (MC) to return to the kiln spec -- if ever?
A.
Yes, the lumber will immediately begin to pick up moisture. As a quick rule of thumb, large pieces of lumber in a tight stack will regain about two-thirds between the KD MC and the environment's EMC in about 4 to 6 weeks. It depends on many factors; this is just an estimate.
It seems that the rate of regain is faster than the rate of loss. Plus, regain results in swelling while loss results in shrinking, and usually, shrinking is a more serious problem than swelling for many wood products.
Also, a small piece of wood will gain moisture back much faster.
You might want to check out the video "Moisture and Wood" from the Wood Component Manufacturers Association.
Gene Wengert, forum moderator
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Have you reviewed the related Knowledge Base areas below?
KnowledgeBase: Lumber & Plywood: Storage
KnowledgeBase: Primary Processing: Air Drying Lumber
KnowledgeBase: Primary Processing: Kiln Operation
KnowledgeBase: Wood Engineering: Wood Properties
KnowledgeBase: Knowledge Base
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