Sawing and Drying

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6/4 8/4 maple drying

4/16/14       
Kevin Member

I tend to dry some thicker soft maple in the 6/4 and 8/4 range. I have had problems with the boards ending up white on the outside, but grey in their cores. I keep my kiln temps below 107 (usually below 100 at first), and my RH well below 60% until the MC is below 20% then I raise the kiln to 120F. In addition to the two fans provided by nyle, I also added a 3' dia agricultural fan and three pontoon fans that I have set up blowing directly through the 5' wide lumber pile, yet still end up with the grey cores. I never overload the Nyle 200 either. I always keep the 6/4 and 8/4 loads to 500 bd ft, or less for at least a week before I add more (4/4 and 5/4). I had this problem throughout this past winter when the temps here were brutally cold as well as in the summer. I do not have this problem with my 4/4 and 5/4 maple. I read that 130 F kills the blue stain mold that I believe is the cause of this discoloration. Should I go off schedule and start the kiln at 130 F? It should also be noted that the lumber goes directly into the kiln from the mill. I have found that chemically spraying the lumber does little good. Thank You.

4/19/14       #4: 6/4 8/4 maple drying ...
Gene Wengert-WoodDoc

The grey core develops because you are not drying the wood fast enough in the middle part of the schedule. After the first day or two, you need to drop the RH so that the core will dry as quickly as the shell did. (Also, remember that it is the actual RH that counts and not the setting.) OK?

4/19/14       #5: 6/4 8/4 maple drying ...
Kevin K Member

Thank you for the response Dr Gene. I would surmise then that I should keep the kiln temps low at 107 F which in turn keeps the humidity low. In the past, I would keep the kiln at 107 until the core was at 18% then raise the kiln temps to hasten the drying time. From what I have recently read this core discoloration is bacterial, and not fungal as I thought it was. Thinking it was fungal, I thought it was okay to raise the kiln temps when the MC was below 20%.

4/19/14       #6: 6/4 8/4 maple drying ...
Gene Wengert-WoodDoc

It is not fungal and it is not bacterial either. It is a chemical oxidation of the sugars and starches in the wood. You are indeed correct that 107 F is ideal. You have to drop the RH however. After you reach 25% MC AVERAGE MC, then you can safely increase the temperature.

4/20/14       #7: 6/4 8/4 maple drying ...
Kevin K Member

Thank you again for your help. My MC of my hard maple is at 24% right now and my wet bulb is at 110F and my RH is at 24%. I also run a dehumidifier in my kiln in addition to the Nyle to get the ambient RH dried down quickly. At what RH would you say that the core staining occurrs? Is it anything over 60%? How long do you have at this RH before you have problems. The mills here cut maple M-W then ship to the kilns, or call me Wednesday afternoon. I wonder if this is too long to wait. I buy from 9 different sawmills and they all run like this.


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