I have the chance to purchase some rough sawn, black walnut that has been air dried for about 1-2 years at a reasonable price – about $2/bft. When I was looking over this stock the sawyer tested the wood with a moisture meter at 13% EMC. The sawyer gave me a few smaples to take home and so I milled the rough sawn 4/4 stock to 3/4 inch and cut some different sized pieces to test them by drying them in a lab oven to constant weight to verify the EMC. Sure enough, this method confirmed the EMC at an average of excactly 13%.
So my questions are as follows:
(a) This wood has been sitting in the open air for over a year and developed a very thin patina of pretty ucky grey – is this a problem?
(When this patina is milled off there is an absolutely gorgeous hue – with a purplish ovetone – that develops in air dried walnut.
(b) Can one you work with air dired walnut at 12-13% EMC or would you continue to dry this to a lower EMC before beginnning to make stuff with it?
(Seems to me that it’s might not be easy to get much below this EMC with air dried stock without waiting for a very long time in a very dry place!)
Replies
All of your questions and many more that you haven't gotten to yet would be very well answered by Bruce Hoadley's book "Understanding Wood". If you are going to get serious about woodworking it is a must read.
John W.
Hoadley's book as John suggests is very good if you're seriously into understanding wood. Not everyone wants to get that deeply into the subject, but you may want to.
But to your question, 12- 13% MC is a bit on the high side really. I generally suggest that for indoor furniture you're generally best to aim to use wood at somewhere around 8- 10% MC.
This is at about the middle range of typical indoor furniture MC. Depending on where you live, seasonal fluctuations, air conditioning/heating use, et cetera, I'd expect in service readings ranging from about 5-6% to 12- 13%.
A very dry climate such as Arizona might eventually yield readings about 6% and shipping the piece overseas in a container-- or an unheated bedroom in a northern European winter, might yield you 12%. Building furniture using that middle 8- 10% range allows for some expansion and some shrinkage reasonably comfortably.
If you want to use the stuff in a hurry, you can speed up the drying process by partially preparing (squaring and thicknessing) your rough 12% MC sawn boards to 1/4" or 3/8" oversize and stickering the resulting planks in a dry area, e.g., workshop/house for a week or two. Get them down to final size at that point and reject any obviously problematical pieces.
If there's no hurry, the 12% stuff can be stickered somewhere dry until it works its way down to that 8- 10% MC point. It will probably only take a few weeks in a typical residential type environment with typical residential type relative humidity (RH) readings. Slainte.
Sgian, I see we got caught in the door jamb again with roughly parallel posts.
Your point about taking the wood's MC down to sightly below the MC level that the finished piece will experience for its average Equilibrium Moisture Content (EMC) when it is put in its final in-use environment, is good advice. It allows the wood to expand slightly, which makes joints snug up...and it also means the wood will experience a little more compression stress than tension stress in its final environment...which is the better way to go, because it minimizes the risk of checking (splits in wide panels, etc).
Here in the upper Midwest, one of the simplest "low tech" ways to achieve this is to schedule the making of pieces that have wide edge-glued panels, or other features that might be a problem (joints with broad cross grain surfaces) during the winter time...In centrally heated homes, that's when we experience our most arid conditions.
John's comment about Hoadley's book is good advice...But just to give you a couple of quick answers...4/4 walnut that has been air dried for approximately two years should have an MC that is in equilibrium with the environment. It should be safe to use, if you intend to use it in that same environment. As a practical matter, though, you should probably bring it inside and let it acclimate to the humidity conditions in your shop for a few weeks before you actually start working with it.
Walnut is one of our more stable domestic hardwoods and it has an exceptionally low T/R ratio...which means it's not very prone to distortion when exposed to changes in relative humidity.
As for the gray color of the rough sawn boards, this is just surface oxidation and it poses no problem. Walnut is also one of the most decay resistant of our domestic hardwoods...so there is little to worry about with respect to decay or sticker staining. If the wood is at 13%MC, this wouldn't matter anyway, since the fungi that cause spalting and decay go dormant when wood drops below an MC of about 20%.
...And Novice, remember this moment well...because you've just experienced one of woodworking's greatest pleasures; being surrounded by the aroma of freshly planed, air dried walnut...and seeing for the first time its beautiful chocolate brown and magenta highlights. You'll never be a virgin again. :O)
Edited 8/25/2004 10:27 am ET by Jon Arno
"...And Novice, remember this moment well...because you've just experienced one of woodworking's greatest pleasures; being surrounded by the aroma of freshly planed, air dried walnut...and seeing for the first time its beautiful chocolate brown and magenta highlights. You'll never be a virgin again. :O)"
Hear! Hear! Truer words were never spoken.
Depends where you live like one of the of the posters said. Here in Florida wood seems to equalize around 12% even if it comes from the kiln at 6%. In a heavily air conditioned setting here, I've measured 10%. Take it inside and let it sit for a few months and see how it adjusts.
Mike
In most places you still have 3 good weeks or hot weather. If your house attic is up to it, sticker a winters worth of woodworking wood, 50 bd. ft. or so, in your attic for 10 days or so, I'll bet it will go below 7%. Enjoy...Dale
>>"In most places you still have 3 good weeks or hot weather. If your house attic is up to it, sticker a winters worth of woodworking wood, 50 bd. ft. or so, in your attic for 10 days or so, I'll bet it will go below 7%. Enjoy...Dale"<<
Good advice...But make sure the wood you stick up there has already experienced most of its air drying and is comfortably bellow about 18%MC...both for the wood's sake and your house's sake.
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