Hello
I am lost in the woods and need some directions. I recently felled a walnut tree before it had leafed out. Last fall it had many branches with no leaves and a large number of suckers growing around the stump so I assumed it was on its last legs. We have sawn it into 2″ slabs and got about 1000 bdft of beautifully figured lumber out of it. It has been stickered for a month in the foothills near Clovis ,CA. It is in a barn with plenty of air circulation and a fairly dependqable breeze. We checked the humidity when it was wet and stickered and it went off the scale of the meter (Over 25%). When we checked it after a month of drying the meter read 16 to 17%. We checked some 4 /4 pine that had been in the barn for 10 years and it read 4% , a piece of pine (8/4) that had been cut and stickered for a year read 8%. I have never heard of air dried lumber getting as low as 4% and would not have expected the walnut to get down so low so quickly. Do we get a new meter? Check it against another meter? The national weather service says that relative humidity for Clovis is 70% in the mornings and 10% in the evening and averagew 30% for April. The lumber is stored in a rural area not close to the irrigated agricultural land around Clovis so I would expect the readings here to be a bit lower. Any guidance would be of great value I can not wait to get to work on this wood! Thanks
Skip Benson
Replies
Cut off a chunk, get a postage scale and check your meter.
Weigh the freshly cut piece, then place it in oven or microwave on low setting until it no longer loses andy weight. Then weigh is again. The difference between starting and finish weights is the per cent M/C.
“When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think...that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ --John Ruskin.
We test our dried pistachios for moisture content by cooking and weighing until we get a constant weight. However, with wood, keep it no more than about 250 degrees F to get an accurate moisture content. If wood gets too hot, it "destructively distills" losing methanol and other chemicals and giving you bogus moisture content results.
>> The difference between starting and finish weights is the per cent M/C.
The difference between starting and finish weights divided by the finish weight times 100 is the percent MC.
((start - finish) / finish) x 100
Hard to imagine that 4% figure (on the pine) being accurate, even after all those years, but then you're in the Fresno area, right? Dry as a bone down there! Are you using a pinned or pinless meter? When you checked the 4x4 pine, did you make a fresh cut first??
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Another proud member of the "I Rocked With ToolDoc Club" .... :>)
Skip and Barbara,
That seems awfully fast for air drying. I take it end and surface checks aren't being a problem. Personally, I'd forgoe the meter and just be patient. Give the stacks until the end of summer....and then surface a board or two. That should tell you if they're ready or not.
Skip, You can't go by the surface only. You will need to use some of your wood tor testing. I hop you coated the ends to controle splitting, but cut a board off about a foot from the end, and check the MC.in the middle. Even better cut out a perfect board foot, then oven dry it then use it to compare the weight of other controle specimen.
You don't want to dry it too fast. It can dry faster on the surface, than the moisture in the middle can replintish the surface. This causes surface checks. We woodturners put our work in a paper bag for the first week or so to slow it down to avoid this. I bring my best work or the most challenging work to my bedroom. I can hear it check in the night, and take action.and I know it is time to take measures to slow things down..
If you havent read Bruce Hoadley "Understanding wood" this may be a good time.
My guess is that you may be going a little fast. The easiest measure would be to cover the stack with a tarp for a few days if you feel the same.
I would go into the second layer, and pull out a board, surface it, look at under at least 10X magnification ( slide loope) measure a controle amount, cook it weigh it measure loss etc, and compare. ( A 1/2" cross crain wafer can be Zapped in a microwave for a couple of minutes to reach oven dry. Use the same board for each test. Change in ring orientation will vary shrinkage.
Have fun. Any knowlege that you don"t posess is a part of yourself that you haven't met yet.
You already have a moisture meter, If you don't have a gram scale, and a dial caliper, both are good insturments for monitoring MC.
Skip,
You haven't mentioned doing this so I'll put it up.
To avoid rapid drying and shrinkage cracks developing on the end of the slab, seal the end grain with a proprietary sealer or simple varnish/oil paint.
The 16-17% would be believable if you were taking measurements at the ends of an unsealed slab.
Must fly, hope this helps,
eddie
I hate to disagree with someone, but Uncle Dunk needs to check his refrences, MC is the amount of water in the wood relative to, or expressed as a % of the oven-dry weight. The starting MC is a variable that is irrelevant.
I beg your pardon for the disagreement.
Rootburl,
I think you've misunderstood the use of "starting weight", which I take to be the weight before going in to the oven. The difference between this and the final weight will be the weight of the water lost.
>> I hate to disagree with someone ...
The trick is to disagree without being disagreeable. :)
>> ... but Uncle Dunk needs to check his refrences
That seems somewhat disagreeable, but no big deal.
>> MC is the amount of water in the wood relative to, or
>> expressed as a % of the oven-dry weight.
That's the way I understand it.
>> The starting MC is a variable that is irrelevant.
I disagree. The starting MC is the very value you're trying to calculate.
Consider a piece of wood that weighs 9 pounds. Dry it in the oven until the weight stabilizes and it weighs 8 pounds. The difference between the starting and ending weight is 1 pound. By the formula Bob gave in message #2, the percent MC is 1%, which I think we all agree is not correct.
The MC expressed as a decimal fraction of the oven-dry weight is the weight of the water, 1 pound, divided by the oven-dry weight of the wood, 8 pounds, which is 0.125. Multiply that times 100 to convert it to a percentage, and the starting MC was 12.5%.
My guess is that this process is so familiar to you that it has become automatic, and when it comes time to explain it, you leave steps out. My goal was to supply the missing steps, without being disagreeable.
Edited 5/5/2004 6:50 pm ET by Uncle Dunc
Edited 5/6/2004 6:08 pm ET by Uncle Dunc
Uncle you are right. I think I misread your post. After midnight, I guess I wasn't thinking too clearly. Please accept my appology. Cheers K
>> After midnight, I guess I wasn't thinking too clearly.
Well, If I'd never done that, I'd be really mad. ;)
>> Please accept my appology.
Happily.
I make gunstocks and buy a fair amount of 3" and 4" walnut. After a year or two you will still get wet shavings out of them. Most people air dry walnut for 5 years for gunstocks. For really fine work a decade or two is better.
I bought some green lumber that was 6 months to a year old, kept it a year (20 feet off the ground and in the hottest air in a warehouse) and tried to work it. Again, wet shavings....
Hope this helps!
Our rule of thumb downunder for air drying timber in thick board dimensions is this.
1 years air drying time per 1 inch thickness thru the thinnest dimension plus a year.
Hence a 2 x 4 would take 3 years to air dry to a little above 13% EMC (Equilibrium Moisture Content).
I like to kiln dry my timbers down to 10% and then allow to reabsorb up to 12% EMC for furniture.
It's likely a high % for those of you in the Northern hemisphere, with snowfall and hence low relative humidity - for whom a much lower EMC% would be desirable no doubt.
Something to recognize with air drying is that a lot of the free moisture will come out and most of the intercellular moisture - but the intracellular (in the cell wall) will not without kiln drying in most instances.
The Intercellular moisture has to diffuse out thru the lumens (pores) in the cell walls. It does this too fast if the free moisture is removed too quickly (i.e. if left in the hot sun while green straight off the saw..you will see and hear it surface check in front of your eyes and ears.
What happens is this - the air movement evaporates moisture from the surface of the freshly sawn green lumber. as a result - free moisture from between the cells is wicked to the surface, to in turn be evaporated away by dry air movement.
As a result the moisture drops throughout the wood on a gradient from the insides to the outsides.
As the free moisture is wicked to the surface it creates a slight vacuum between the cells. If there is sufficient time and low enough vacuum and enough heat - the moisture trapped within the cells (inter cellular moisture) turns to a gas (steam) and is forced out of the lumens (pores) in the cell wall, into the vacuum spaces left by the removal of free moisture (sap), and in turn wicks it's way to the surface of the board and is evaporated.
If the free moisture is removed too fast under high temperatures, the gaseous moisture inside the cells burst thru the cell wall to fill the vacuum in the free moisture spaces, and we get what's known as structural collapse of the timber - and this is usually seen as a depressed powdery texture to the wood in the centre of the board full of long checks thru to the surface.
This condition and this form of drying applies to both kiln and air drying if not adequately controlled - I'd imagine in snow country with zero relative humidity it could also be an issue in winter.
With kiln drying - the last type of moisture within the timber - that trapped in the cell walls made of cellulose - (intracellular moisture) can be removed with vacuum dehumidifying kilns over time. usually this moisture doesn't come out with air drying unless undertaken in almost desert like conditions of very high heat and very low relative humidity for prolonged periods.
We work it this way - we can air dry down to a suitable EMC for Joinery work (door Frames, solid doors, window frames & sashes etc) where some limited movement after manufacture and during installation etc is acceptable, (Joinery usually is exposed to weather extremes while the bricks are laid, and roof put on until lockup.
All that protects them after manufacture during the building phase is a light spray of linseed oil straight after manufacture until lockup..so removing that last Intracellular moisture from inside the cell walls is wasted time effort and $...Air dried is sufficient for Joinery.
However for solid timber furniture manufacture where stability is more important (critical?) we do kiln dry to remove intracellular moisture since hopefully the furniture will never see exposure to weather.
Your moisture readings to me sound waaaay too low to be accurate in the shot space f time since you slabbed out the tree..I'd be getting new batterys for the meter and retrying and I'd also borrow someone elses meter and test against it.
Do you allow for Hot wood (+1.5%) up to 21degrees C plus 1% for every 11 degrees C above 21 degrees?
Also - most neters are graduated for oregon so dense tmbers like Walnut will likely need a correction factor due to their high SG (Specific Gravity) probably adding another 5 or 6%..
So for example, a reading of 4% on the meter if the woods hot straight from an oven / kiln could be a proper reading of 4% reading + 1.5% Temp to 21 degrees C + say 2% for temp to 43 degrees C, plus say 6% correction factor for density of walnut = say, 13.5% moisture content reading, and even that sounds waaaay too low - your meter must ne a long ways out - you need to get it calibrated against one that is working right in my best guess.
my 2c.
Cheers!
Edited 5/6/2004 12:41 am ET by trouty
Trouty>
Thank you for the infrmation on drying. You confirm about what I have been thinking. I do think we may have optimal air dyring conditions ,warm weather near 100 daily,good air movement yet out of the sun and weather but things seemed to be moving too fast. We had calibrated the meter for different the specific gravities of the wood but didn't do anything about the heat as it was over 100 the day we took the readings. Will try checking against another meter but we had put in new batteries for our checking so that should be O.K. Any way thanks for a thoughtful and informative reply. What do you do beside reply toquiries on the internet are you a woodworker?
SKip
Yes I'm a woodworker, but a lazy one. I was a forester 8 years, been wood working full time last 9 years, taught by my late father. I have no trade qualification, since I started in partnership with Father and thus didn't need one, now I own the business, so i guess I still don't need one.
I sawmill & kiln dry lumber and then manufacture it into fine solid timber furniture.
Basicsally I can take a log from the forest floor to the showroom floor (whats it called?..vertical integration, I control the entire process from go to woah).
I also do Cabinetry (Kitchens vanitys wardrobes etc) and solid timber Joinery as well.
Dad was a master builder so i had a pretty good grounding in most of the trades over the last 17 years working part time with him while I was a forester for the Govt for the first 8 years while we built our factory, and then full time the last 9 years since I left Forestry, until he died this January just gone making furniture joinery and cabinets as the demand dictates.
Throw in milling and drying lumber I probably know just enough to be dangerous...but i get bye.
Now he's gone I realise just how much I Don't know! (and am learning even more every day now....having to do all the measuring, quotes, materials ordering, cutting lists, sheet maximisation and so on myself, which he always used to do).
Anyway - as I said I get bye.
Hope the Walnut works out for you, as a forestry consiultant a few years back I had a 12 month job develping land & establishing a commercial walnut plantation. The timbers worth a LOT of money over here as no doubt it is over there - my advice hopefully will help you avoid damaging the walnut during drying - i hope so - sounds like you have a good dryingenvironment.
I use one of the Tramex wood encounter moisture meters - the non destructive induction model - you can google search them.
Best of luck with it.
Cheers!
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