Notes on wood care, use, and drying.

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Brian
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Re: Notes on wood care, use, and drying.

Tue Feb 28, 2017 5:11 pm

Good list and certainly some things to consider!

Being that I purchase from lumber yards I tend to stick to yards that I know well for quality, and also to buy what I can early on so that I can stack it in the shop until it is used for commissions.

Recently I purchased some AYC intended for future use as shoji, I expect it will be in the shop for a while.

I've had some 12/4 walnut stored for a few years now, I'll leave it go as long as possible. I have some other walnut I've been buying up as well.

Also nice to buy from places that keep a lot of stock on hand so they're not simply churning new inventory constantly. One of the sawyers I work with has had some stock for years and so it's nice to use stuff from him as it is very well kept and properly dried.

Even still in the dead of winter I will see joints that could be tightened up further. I've been moving away from glued joints as often as possible to take advantage of this situation when I see it, and tighten up joints that show a gap in the driest time of the year.
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Re: Notes on wood care, use, and drying.

Wed Mar 01, 2017 6:58 am

Great info Jacob, thanks!

I'm interested to hear more about the felling/drying process. How long after felling might a log be sawn? How is it treated before further processing?

When you said
-If the tree can not be immediately removed it will be left as is for two years with limbs uncut to reduce checking
, do you mean up to two years? Or at least two years? Exactly two years? Are any precautions taken to prevent fungal growth? Interesting about leaving the branches on, is that just to keep the log up off the gound, or does it have to do with the tree's biology/structure/moisture distribution, etc.?

-Matt
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Re: Notes on wood care, use, and drying.

Wed Mar 01, 2017 7:01 am

Also, what kinds of hygrometers are found in japanese woodworking shops? The cheap ones I've used are notoriously inaccurate. But how accurate does one need?
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Brian
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Re: Notes on wood care, use, and drying.

Wed Mar 01, 2017 8:51 am

Daruma wrote:Hey Brian,

My guess is if things are tightening that much in winter that the wood is not quite dry, but as you say it is one of the best times to work as the air is typically dry.
I have also been ruminating a post about hand hewing a log if your interested but that will have to wait until the snow melts in late spring. Instead of using a band saw I will first rip the sides with a chainsaw and then mark and hew.
The other interesting thing I came across the other day in the hardware store was a step by step look at making a sumitsubo in a tool magazine. Maybe if people are interested it could be a kind of study project. Lots of chisel work as its dug out entirely by hand.
It's dry, but I work in my basement with the forced air heater in the next room, so it really dries the place out. I have my cigar humidors in the same space (other side of the wall) and end up refilling them with water quite often during the same time period.

So, while dry, no wood can be dried to the degree that it won't shrink a bit in this type of condition. If I were in an outside shop, such strange things would likely never happen. In fact, if I simply move the furniture from the basement to the top floor many of these issues will disappear over the course of a couple days. Crazy, right?

I'm very interested in both the log hewing and also the cutting out of a sumitsubo! Thanks for considering posting on such topics.
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Brian
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Re: Notes on wood care, use, and drying.

Wed Mar 01, 2017 10:36 pm

That's not a bad plan, I think I'll give that a shot.


I pretty much do work in a kiln in the winter months, which is occasionally an advantage. If I make something in winter in generally tightens up when it leaves the shop, an effect I quite enjoy.
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Chris Hall
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Re: Notes on wood care, use, and drying.

Sat Mar 11, 2017 8:33 am

-Felling is usually done in winter and ideally in freezing conditions when moisture content is at its lowest
It is a common misapprehension that moisture content of trees is lowest in the winter, however this is false.

Quoting Professor Gene Wengert:
The amount of sap in a tree, or the moisture content, is essentially the same throughout the year. This has been measured time and time again, especially by pulp companies that buy wood by weight and are sensitive to the amount of water in the tree when pulping. The sap does not go into the roots in the winter. In fact, with some species we see a 1% MC increase in the wood above ground in the wintertime. The difference between summer and winter is the flowing of the sap.
As one example of some species in which we see an increase in MC during the winter, there is Aspen,

(see: https://www.forestry.umn.edu/sites/fore ... tes_19.pdf)

Quote from paragraph 1 of that piece:
Recent investigations have shown that the wood moisture content of one common Minnesota tree species (Populus tremuloides Michx.) undergoes
large seasonal variations. These studies have shown that for this species the period of high moisture content occurs during the fall and winter~rather than during the spring and summer.
Further, freezing temperatures have no effect on the sap for the most part. Quoting Wengert again:
Also, a similar issue is that the sap does not freeze in the wintertime in the tree. It has natural anti-freeze. We may get some freezing under -40 F and then trees will get so-called frost cracks due to expansion of the ice.
Most of a tree is a dead scaffold of tissue converted by extractives, hardened off after a season's growth. The highest moisture level is found in the current growth layer, and associates primarily to the sap. The sap is always present.
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Re: Notes on wood care, use, and drying.

Sat Mar 11, 2017 10:52 am

-Kiln dried wood is not considered an option and only properly air dried wood is used
This is fine if the environment in which the constructed piece is to reside is of the same relative humidity as to which the wood was dried. In Japan, where central heating is quite uncommon, and there is a bit of a cultural idea that the house environment should somewhat reflect the outside environment (i.e., stifling/hot in the summer, drafty/cold in the winter), and traditional house construction revolved around maximizing ventilation/air circulation above all else, the relative humidity inside a house is going to largely harmonize with the relative humidity outside, so air dried wood will work fine.

In many other countries however, people do not like to, say, huddle around a charcoal brazier or under a heated table in the winter and prefer central heating and insulated houses. People in the US prefer to keep the house temp relatively consistent - warm in the winter and cool in the summer. Keeping a house centrally heated requires the addition of heat, either blown air or radiant, etc., and thus the relative humidity inside a house is generally going to be lower than what it is outside - or in the case of the area where i live, people will add humidification to certain rooms, like bedrooms, to keep them from getting too dry in the winter. Furniture inside a house is going to be exposed to much drier conditions than eventuate with seasonal air drying cycles.

If the furniture piece is to be subjected to life in a conditioned interior space, that is, a space which presents an artificially more or less dry environ than otherwise, then the wood must also be subjected to a drying process which brings the wood to a low enough moisture content to behave well in that situation, and that means exposure to greater heat and lower humidity than is present in the normal seasonal fluctuation.

The floor in our house is a great case in point. We have a super-insulated double-wall house and we use only a small heater in the main room to heat the entire house. We keep the temperature usually in the 64~66˚F zone in the winter, which is lower than many people do. The wood flooring in our house was locally sourced ash, air dried, and it does not do so well in the winter months. The floor shrinks quite a bit and nearly 1/8" gaps form between boards. It was a warranty claim issue for which we received compensation. When I replace the floor down the line, it will not be with air dried material, regardless of how long it has seasoned.

In general in a North American context, one can consider a typical seasonal relative humidity level in a house to be 50%RH, and if you want wooden items to behave well at that RH level, then the wood needs to be dried to an equilibrium of 8~9%MC.

Some areas of the US, however, are much more challenging, like Salt Lake City, where the relative humidity is so low it is almost impossible to get wood dry enough - the 4~5% zone -that it does not shrink a bit after installation.

Air drying is an important step in the preparation of wood, and may be enough for certain situations.

However, I'll quote a passage now from William H. Brown's The Conversion and Seasoning of Wood, from chapter 6 'Air Drying', where he's taking a look at conditions in the United Kingdom:
It will be seen that the average relative humidity throughout each twenty four hours is in excess of 80% for a large part of the year, equalling a drying equilibrium for wood of more than 17 percent, while the best drying periods are during the daylight hours from March until September, but taking an average for the whole year, relative humidity is 79.5 percent and equilibrium moisture content 16.4 percent, which is in effect about the driest one can expect air dried wood to achieve in this type of situation. The annual averages given are based on Meteorological Office data covering a ten year period, i.e., 1961~1970 and it will be seen that taking the British Isles as a whole, equilibrium moisture content values for wood stored in the open air are a lot higher than is generally realized. The summer months do provide lower equilibrium values and obviously have a bearing on the condition of wood, deemed to be air dry, if extracted from the yard during this time.
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Re: Notes on wood care, use, and drying.

Sat Mar 11, 2017 3:47 pm

I've heard and read repeatedly that felling is best done in winter, but I haven't heard a definitive answer why. The matter isn't addressed (that I could find quickly before writing this post) in the USDA Encyclopedia of Wood or Hoadley's Understanding Wood. Forum posts on Woodweb, etc. seem inconclusive.

But since there's general consensus that felling at least after the leaves fall and before springtime is 'best', there must be something to it. Some say it's gotta be between the autumn equinox and winter solstice. Some say moon phase is important. The moisture content thing gets repeated often. Another plausible explanation is that when the 'sap is down' (which I gather means that the sap isn't flowing- different from low moisture content?) there is less sugar in the tree, and so it is less attractive to bugs and fungi. I found one website claiming that cutting at 'half-tide' (between low and high tide) assures that "the sap level is at its lowest", yielding better lumber.

So it seems that there's a lot of tradition, observation, intuition, and hearsay going on here. Anyone have more concrete info? And what might be the consequences of not obeying the conventional wisdom? Surely it happens all the time... and I've surely seen a lot of crap wood out there...
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Re: Notes on wood care, use, and drying.

Sat Mar 11, 2017 4:51 pm

Well, there are a cluster of reasons as to why cutting trees in the winter might make the most sense. In agrarian times it would have been a time of year when farmers had more time available for such work. Trees are easier to drag on the snow and the snowpack can make navigating the understory brush much easier. Logs can be left on the ground for a time without worry of boring insects getting a hand in - so this makes the issue of "sap is down/less sugar in the tree, and so it is less attractive to bugs and fungi" rather moot, since in the winter the activity of insects and fungi is greatly reduced or entirely removed simply by cold temperatures, with no connection to sap in the tree.

The moisture content issue associating to sap and season is simply a widespread misunderstanding about sap in trees and has been debunked as far as I am concerned.

Those that talk about moon cycles and the like relating to tree moisture content have all the room in the world to prove their case, as it would be simple enough to measure moisture content over the cycles of the moon and see what variance there might be. Still waiting on that study.

One thing about winter harvested trees is that they are harder to de-bark.

Crappy wood can of course be produced by kiln drying, but this is nearly always the result of the kiln operator cutting corners to make money and not observing proper drying cycles.

When Len at Eastwind first got back from Japan and built his house, and was featured in Fine Woodworking in 1981, the author (Chuck Miller) wrote:
"The green boards were then carefully stacked to air dry. Only air drying will do; kiln drying affects the workability of the wood, resulting in a condition that Brackett likens to "drinking flat beer - there just isn't any fizz in kiln-dried wood"
Now, moving forward to Brackett's 2005 book Building the Japanese House Today, the tune has changed somewhat:
"Kiln drying, which generally speeds the drying process, as opposed to air drying, also has its place in this kind of construction."
On the next pages (88~89) he extols the virtues of radio-frequency vacuum kilns:
"A benefit of the RVF kiln is that it precludes the need to keep a huge inventory of timbers on hand: only the lumber needed for the building being constructed needs to be prepared. Considerable capital is needed to acquire and store large inventories, and this is a business cost that ultimately affects the cost of the house. In addition, while stored inventories offer many advantages, they also need constant care and protection from the elements, and they are almost always made without a specific building in mind, based on speculation that the lumber will eventually be used in some project. Another problem with an inventory of dry lumber is that if smaller timbers are required but aren't on hand, then large timbers must be resawn, which results in considerable mill scrap, a great waste of this precious material. It would be far less wasteful to mill the smaller timber from logs and to dry them immediately. Additionally, in the air-drying process a certain percentage of the lumber will be unavoidably degraded through checking, blue stain, or other discoloration; the kiln-drying process makes this less likely."
And in regards to,
So it seems that there's a lot of tradition, observation, intuition, and hearsay going on here. Anyone have more concrete info? And what might be the consequences of not obeying the conventional wisdom?
I'm personally not much for the superstition and folklore side of things. Wood is a major commodity of interest to a lot of entities and has been studied in depth by scientists for a long time - though there remain unsolved mysteries - and its an incredibly interesting and fascinating material without all the superstition added in. I tend to go with what is provable and demonstrable, and can be replicated by others, not by hearsay.
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Re: Notes on wood care, use, and drying.

Sat Mar 11, 2017 6:30 pm

Can One still deduce that given enough time the moisture content will come down that low( 4-5%) or not?
It's not a matter of time so much as the environment in which the wood is stored. The the RH of the surrounding environment never goes below 60%, say, then no amount of time in air drying is going to bring the wood below about 10.5%. To obtain equilibrium moisture content of 4~4.5%, the RH needs to be 20%.

Here's a map of the US showing averages for RH - as you can see, no part of the US is as low as 20%, though Southern Nevada-Death Valley area comes closest:
Mean Relative Humidity (Annual).png
Mean Relative Humidity (Annual).png (157.06 KiB) Viewed 5816 times
I guess Las Vegas is the driest urban location in the US, with annual RH of 30.3%, which matches a wood with equilibrium moisture content of about 6%. That's very dry wood.

And here's a table for some Japanese centers, as you can see, nowhere is lower than 57% RH (Tokyo), which correlates to a equilibrium moisture content for wood of 10.6% or so, and most areas RH are significantly higher:
a12tab02.jpg
a12tab02.jpg (94.38 KiB) Viewed 5816 times

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