Q: We have some veneer checking in our finished veneer. It's about 8 percent MC, and we keep our plant at 40 percent RH and seldom see any problems in the plant. The problems seem worse after the product is installed.
A: To crack dry wood, especially in the middle of a piece, requires quite a bit for force. Dry wood that is not already cracked is not easily cracked. In fact, if the veneer you have is 10 percent MC when it comes and your plant is 8 percent EMC, that small difference is not developing enough force to break the wood. Likewise, even if the customer has 6 percent EMC (= 30 percent RH), that will not create enough shrinkage as the wood dries down to 6 percent MC so develop enough stress to crack the wood.
So, what we have with 99 percent probability is that the veneer you have already has some small checks in it. These could be from the lathe (and called lathe checks and caused by improper nose bar pressure at the lathe when the veneer is peeled) or it could be from improper drying. With these preexisting checks, any drying that occurs after you finish the veneer will result in shrinkage and opening of these preexisting checks.
I suggest that you might want to put a few samples of your incoming veneer into an oven at 110 to 120 degrees F. After an hour or two, these pieces will shrink quite a bit more than they would in service. Any preexisting checks will open, but the shrinkage will not generally be enough to create new checks.
I hope you are measuring the RH with a good instrument. I suggest that you purchase a RH and temperature sensor from a local retail electronic supply house. These sensors are exceptionally good.
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