Q. We purchased some eastern white pine lumber and are finding wet pockets. Can you tell me what causes them?
 
A. Wet pockets in white pine (we also see them in aspen and cottonwood, elm and a few other species) are small zones, maybe 4 inches long and 1 inch wide in the interior of lumber, that can have moistures of 15 to 20 MC while the rest of the piece and the rest of the lumber in stack is at the correct final MC value. A major problem with these wet pockets is that the water will eventually leave and with that loss come a bit of shrinkage after a product is made and finished…potentially a defect.
 
Wet pockets have been associated with a bacterial infection that is in the living tree. These bacteria increase the moisture content where they are growing and also create a bacterial slime that prevents the moisture from leaving this zone as rapidly as from uninfected wood. So, at the end of a normal kiln drying run, there are these small pockets of high moisture within a piece of lumber.
 
 

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The moisture difference can be minimized by drying longer and at temperatures over 170F. However, longer drying time means more money is spent for drying ($20 per day per 1000 BF typically, so a 30 MBF kiln that means $600 per day). Is minimizing wet pockets in a few pieces worth $1200 to $1800 dollars (two to three extra days in the kiln)? Probably not.
 
 
 
So, a user of the lumber should consider using a pinless moisture meter to locate and eliminate the pieces with wet pockets from production. Putting these few pieces in a warm, dry location for a month is usually enough to allow the pockets to dry out.
 
Special note: Sometimes the wood in and around a wet pocket ends up being weaker, due oath bacteria. This may create some fuzzing and uneven staining issues, and may a few other manufacturing and performance problems. Thank goodness that wet pockets are usually rare.

 

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