Wood MC Puzzle

[David Ilvedson]

If it's too dry your not basting it enough...;-]

Happy TG

David I.

On 28 Nov 2002 at 11:14, Farrell wrote:

> 
> I'm trying to figure out why a piece of wood is not behaving itself.
> 
> On 11/6/02 I cut a piece of spruce out of an old soundboard and sanded
> the finish off. It weighed 91.71 grams. Environmentalconditions in my
> shop, where the soundboard had been for months were pretty constant at
> 75EF and 45% relative humidity (RH). According to Dept. of Forestry
> data, wood under those conditions should have a moisture content (MC)
> of about 8.4%.
> 
> I driedthe sprucein my kitchen oven to zero MC (monitored weight
> periodically until no change was noted for about an hour). The oven
> temperature cycled from 210EF to 250EF (set the oven to 225EF) during
> the four-hour drying process. When dry, the spruce weighed 84.55
> grams. Working backwards to calculate the MC before drying indicates
> the wood was at 8.47% MC - real close to what the Forestry data
> suggested it would be. OK so far.
> 
> I took the spruce out of the oven at zero MC and set it in the shop
> and periodically weighed it and calculated MC. Last night, after three
> weeks of regaining moisture in my shop, the spruce weighed 89.80
> grams. This calculates out to a MC of 6.21%. Three days ago, the wood
> weighed 89.76 grams, or a MC of 6.16%. Clearly, the rate of moisture
> accumulation in the wood has almost leveled off. Not OK now.
> 
> The shop has been consistently at a temp of 65EF and RH of 45% for
> weeks now. That should equate to a MC of about 8.5%. I find it hard to
> imagine that my little piece of spruce will gain enough moisture in my
> lifetime to get back up to 8.4% or 8.5% MC.
> 
> Anybody have and great ideas of why the wood seems to be staying dryer
> after the cooking process? Is 250EF too hot - has it changed the wood
> somehow so that it can't hold as much water? It looks the same. What
> is going on? Anyone know a professor of wood technology?
> 
> Under what environmental conditions do commercialwood drying kilns
> operate?
> 
> Thanks.
> 
> Terry Farrell
>