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Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Lumber Degrade Above or Below FSP Question
Forum Responses
As far as checks are concerned you need to remember two things. 1) When you talk about fiber saturation point you can only talk about each cell, not an average moisture content of a block or board of wood. This is because the surface is usually drier than the center. So, only one point through the depth is at FSP. 2) Shrinkage does occur before you reach FSP when the wood is initially dried. So you can have wood shrink above FSP and cracking occurring. And the most critical time during drying is above FSP.
The FSP applies only to individual cells and not to an entire piece of lumber. A piece of lumber, when at 30% average MC, is not at the FSP. Some of the cells on the outside have been below the FSP for days or weeks, while some cells in the center have never reached the FSP. Most degrade occurs when the wood is shrinking, so that would be when some cells are below FSP, even thought the average MC of the lumber is over 40% MC. Gene Wengert, forum technical advisor
Let me say it again...lumber is never at the FSP. Gene Wengert, forum technical advisor
Avoiding the term FSP completely, you can state that most kilning-related degrade is caused during the initial part of the drying process.
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