I finished the first load in the kiln today, 360 b/f of air dried Red Oak. I have a freshly sawn load of Walnut to go in next. It is 270 b/f of 4/4 lumber and some 4/4 slabs. After stickering yesterday, I checked the moisture level, and the meter showed 34%. After a full day and night, this morning, I checked it again. It now shows 32%. Does it really dry that much in one day? Should I let it air dry some more, or put it to cooking now? The oak dried from 15% to 7% in three weeks, without fans or DH running for most of the time.
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Don't want to ruin this load of Mississippi Walnut, cause it's highly valuable!! Still a lot to learn! Andy
How accurate is your meter over 30%? Many of them have trouble reading high moisture content like that. That can tell it's over 30%, but not with much accuracy. As the wood dries down it gets into the range where they can measure accurately.
Ian
Andy, What Ian says is right... no good reading over 30%, and that is stated in the specs for the MMC210
http://www.wagnermeters.com/shop/wood-moisture-meters/mmc210-digital-proline-moisture-meter/
Above around 30%, as I understand, the cell walls are at their max mc, and any water is free water in the cells, not the walls. Same reason that there is not shrinkage until the average mc is below 30% (however there are gradients throughout a piece of wood below that "average" that will/can shrink and cause problems).
The wagner meter cannot measure over 32% moisture content. That means that your wood is over 32% moisture content. Your wood is still very green, and until the moisture content falls below 32%, your meter is not registering an accurate moisture content.
Andy, I have some walnut sawn that had been standing dead trees for like 6 + years at least. Its 5/4 and 6/4. The 6/4 measured at 32% on my wag. 220 last week and it has been stickered for 5 weeks. That stuff sure dyes slow on the thicker stuff. bg
Since we're on the subject of moisture content, is there an optimal MC in Walnut that it should be air dried down to before going in the kiln?
Last year I had a green load go in my dehumidifyer kiln and it checked pretty bad. I spoke with WDH and Onewithwood at the Pig Roast and I think we concluded I may have dried it too quickly. Or there was a lot of stress in my logs.
I don't remember asking how dry it should be before going in or if it matters.
Not really. You can kiln dry from green. But you need to be more careful with green wood, and not dry it too fast. If you are pulling moisture out faster than it can migrate from the core of the wood, then you end up with a dry (and shrinking) shell, and the core of the wood still green (and full size). Then bad things happen. This might be what happened with your load? Sophisticated commercial kilns will have some clever control equipment to keep they drying at the max rate for that particular species, and can control the humidity and temperature to control the drying speed, and it's adjusted according to the species and how dry it is.
Once you have the wood air dried to maybe 15%, then it's hard to mess up in the kiln as even the core is 3/4 dried. So things are a lot more forgiving. Depending on your climate you might expect wood to dry down to 10-15%, and then you can do pretty much anything (sensible ) with it.
Ian
I like the wood to be below 25% moisture content before going into the kiln. Once the wood has reached 25%, you are past the worst danger zone for most drying related defects, and you can dry it faster in the kiln.
I agree--You cannot run a kiln using a moisture meter as they are not accurate enough, especially at the higher MCs. You can use a meter to estimate the final MC, but again, due to temperature, density variations, and so on, they are not accurate enough for the requirements of many kiln operators and customers.
The best way to check the MC is to use kiln samples. The technique is detailed in many books, including page 66+ in the book I helped to write, DRYING HARDWOOD LUMBER, which you can find on the Internet in many locations. In fact, as it is out of print, you can give the internet address to a copy store and they can download and print it and even spiral bind it for a very reasonable cost. The safe daily drying rate for walnut is on page 99. For 4/4, it is 8% MC loss per day. Note that for walnut,proper end coating is critical to avoid end checks and end honeycomb.
I was riding the creek yesterday looking for my long lost bridge decking boards. I saw a couple of nice Walnut trees that will need drying. ;D
Ut Oh Andy, did you see that last statement on what someone saw? bg
Bill,
Yes I am well aware of all the commotion going on East of me! I will gladly go help him with the creek bank restoration, and even help recover his bridge boards! All we got to do is pick a good time for all involved in this project.
Lynn,
The last Walnut tree from Mississippi sure made some beautiful lumber! I think I'm going to air dry it for a while before putting it to cooking in the kiln. Don't want it to do bad things! You two try to stay out of TROUBLE!!!
Andy :-[ :-[ 8)
No need to try and rush it. Patience is the word.
And no promises about the "trouble". :D
Of all the wood that I have dried, walnut behaves better than most wood. Compared to oak, it is a dream.
Andy, if your staying out of trouble, your not having any fun. bg
Throw in some 12/4 walnut gun stock and you will have a real headache. Not easy!
Edit: What I should have added is that figured 8/4 might be a little harder. 4/4 is very easy.
Had a great visit with Andy and his wife today to check out his kiln, they made me feel right at home and looking forward to my next visit. 8)