What happens to wood when it dries too much? I almost did it today. From what I understand, 6% is as low as I would ever want to go and I usually shoot for around 8%. I am told that irreversible damage occurs to the structure of the wood when it gets too dry. Does that apply to all species? Reclaimed heat pine (longleaf southern yellow pine) specifically? Mine showed around 6.5% to 6.7% when I checked a few boards in the kiln today.
I turn the kiln on in the evenings when I'm going to be here to keep an eye on it, and leave it off at night and during the day. This evening, I turned it on and forgot about it, but it had already run the previous 2 evenings and the charge was getting close to dry. I think I almost ruined a charge, which got me to wondering what exactly happens when it dries too much.
(Sawing and Drying Forum)
From contributor J:
The desired MC depends on where you are going to use it. In most of the US the desired MC is 6-8%. If there is no checking or warp then there is no danger in going too low. It will take on more water once put in the environment that it will be used in.
The reason I usually shoot for 8% or so is that is what has been requested most of the time. I have tested wood in homes in my area that have been in the home long enough to fully acclimate, and homes in my area seem to keep wood in the 9% to 11% range. I haven't ruined this wood, have I? I suppose I shouldn't be drying less than 10%?
Contributor D - If I understand correctly, you can dry wood to 4% as mentioned, and you can raise it back up by introducing it to moisture, but the damage has been done and is not reversible. I am told cell structure of the wood becomes damaged and the cells are obviously dead now, so they can't be repaired by introducing moisture. Kind of like you can turn iron into rust, but you can't turn rust into iron. So just because the meter says it's back to 10% doesn't mean the wood is the same as it was when it was at 10% the first time around.
In fact, I may be misinformed all the way around. It seems to be hard to find real fact when dealing with this kind of stuff. There is so much conflicting info out there. My main concern right now is determining whether the wood I have at 7% is still acceptable product. If so, should I wait until it gets to a higher MC before milling it? It's for flooring.
You have 60 watts of power? Did you know that it takes about 15 kWh to dry 1500 BF of pine by 1% MC. That is about 10 days with 60 watts running full time. Of course, you are only running part time. Something does not seem to add up here. I really have a hard time figuring how you could actually dry the wood, let alone over-dry it.
I ran a little of the 4/4 through the moulder today with no problems at all. Machinability was the same as always, but this particular wood had a good bit more resin/pitch in it than usual. I think that had a lot to do with the good results. It sure does gum up a machine in a hurry though. I'll run the rest through and see how it does. Most of the wood isn't as sappy as what we ran today, so I'll have a better idea of machinability soon.
So machinability is the main concern about over drying, correct? Structural integrity isn't compromised?
|Common Lumber Name||A||B||C|
|Hickory, Bitternut (Pecan)||14.7||31.2||4062|
|Oak, California black||16.4||26.5||3455|
|Oak, Northern red||13.6||29.1||3793|
|Oak, Southern red||9.6||27.0||3520|
|Oak, Swamp chestnut||10.7||31.2||4063|
|Oak, White||10.8||31.2|| |
|Common Lumber Name||A||B||C|
|Cedar, Atlantic white||10.9||16.1||2100|
|Cedar, eastern red||16.4||22.9||2981|
|Cedar, Northern white||11.1||15.1||1964|
|Cedar, Western red||12.2||16.1||2100|
|Douglas-fir, Coast type||12.3||23.4||3049|
|Douglas-fir, Interior west||13.2||23.9||3116|
|Douglas-fir, Interior north||14.0||23.4||3048|
|Fir, California red||10.6||18.7||2437|
|Fir, Pacific silver||10.4||20.8||2711|
|Pine, Eastern white||12.3||17.7||2303|
|Southern yellow group|
|Pine, Western white||10.0||18.2||2370|
|Redwood, Old growth||14.9||19.8||2573|
|Redwood, Second growth||13.2||17.7||2302|