My Wood Drying Study

[WarmGuy]

I did a study of how long it takes my wood to dry under my local conditions. I took a number of pieces of wood in different formats, and weighed them every month or so. This is the wood:

A - Spruce (or maybe fir?)
B - Spruce smaller piece
C - Pine shorter log, unsplit
D - Pine longer log, split
E - Pine longer log (matched to D), split
F - 2006 log split, that had dried and then gotten wet again (months in the rain)

The picture shows this wood, and the graph shows how their weights changed over time. 0 = Jan 20, 2007. The relative humidity around here (far northern California coast) is very high.

My conclusions:

1. It takes my wood about 5-6 months to dry (reach an equilibrium)
2. The split wood did not dry any faster than the non-split (this was a surprise)
3. The wood that had dried then become wet took just as long to dry

 

[begreen]

Maybe I'm reading the data wrong, but what is interesting to me is the rate of weight decline. Wood F showed the fastest decline. In 3 months it dropped 1/2 its weight and probably was burnable. While wood C took almost twice as long to accomplish the same weight reduction.

Good data, it would be interesting to correlate with different storage methods and have an overlay of the relative humidity on the days when the weights were taken.

PS: can you add your local to your personal info so that it shows up under your handle? It would be great to see your stove in your signature too. Thx for the interesting post.

 

[WarmGuy]

Here's the chart "normalized." I start with the third data point, because I had messed up the first two measurements for some of the logs.

What are your interpretations of the data?

 

[begreen]

wood F appears to have been the wettest and had the most rapid heat loss. It would have been burnable in 4 months. Contrast this to wood D that took a month longer to lose 15% less moisture.

 

[carpniels]

HI Warmguy,

Interesting study. I liked the normalized data better for comparison purposes.

F dried the fastest which is probably attributable to the wetness which infiltrated from the outside after it was properly dried. That moisture was all in the outer layers and therefore would have a small distance to migrate out of the wood.

The stabilization after 6 months is easy to see and seems comparable to my experience here in NY. It is a fast drying wood.

A few interesting things for future experiments:
1) it is always better to do experiments with multiple replicates. That way you can release the statistics on it and get some really cool defensible results. So multiple As, Bs, etc.
2) I would repeat the experiment over a longer time with a regular hardwood. Especially, Oak seems interesting, since that is a notoriously long drying wood.
3) I agree that a test with different storage methods would also be fun to do.

All in all, I probably need to get to work and set up some cool experiments. I wish I had more time.

Carpniels

 

[kjklosek]

It would be interesting to take the same species and dry them in an oven and compare the wet weight to the oven dry weight. Then you could calculate density from this control group and see how that affects the drying time.

Also, different species have a tendency to dry more quickly than others because of their pore structure.

One good example is the comparison of white and red oak. White takes longer since the pores are clogged with tyloses which restricts the migration of water.

Of course that is what makes it an excellent material for boats, barrels and flooring.

J.P.

 

[ISeeDeadBTUs]

And I'll take 'wet' red oak over any of the dried species in the test

 

[wahoowad]

I did a weight-only study this past year for a split of both oak and hickory. I need to get some final weights and see what it says.

 

[Corey]

That is an interesting study.

Looking at your normalized graph, things do seem to be equalizing around the 6 month mark, definitely by mo. 7 or 8. You mention the split wood not drying any faster. This is something I have been saying for years on here – trees are mainly designed to move water up and down, and specifically designed *against* moving water sideways and out the bark. Hence, cutting the tree into firewood lengths has as much effect or more than splitting. In the general probings I have done with the moisture meter, the split surface may dry ½ to ¾ inch deep while the cut ends dry 3-4 inches deep. It is interesting that your split sample started to dry faster…possibly the moisture leaving the very surface of the wood at the split, but then leveled off…again due to the fact that the log just cant move much moisture laterally – it mainly has to go out the ends.

At first, I was a bit curious why some logs normalized at 70-75% of the original weight and some were 45-50. But breaking it down a little it looks like Pine short was 50%, Pine long was 62-ish and Pine long split was 58% - again showing that the shorter length got drier than the longer split wood. The spruce or fir were the higher numbers which maybe says that wood simply had less moisture content to begin with, and it also looks like the smaller split piece (but same length) dried only slightly more, again tending to suggest that length plays more factor than diameter.

It’s also interesting that your already dried log dried at a faster rate. It’s possible that with a dry chunk of wood, water would soak in somewhat evenly over the entire surface, then wick out just as evenly. Another way to say that is you would not have water bound up in the center of the log, because any place it can soak in to, it can just as easily soak out of.

Bottom line – if you want your wood to dry fast, cut it into shorter lengths, splitting is optional.

 

[kellog]

Warmguy,

Great study. Thanks for sharing the study and the procedure. As we have mostly hardwoods here in the northeast, your study will need to be done by one of us to see how it goes for hardwoods. However you really added to the knowledge base and likely will inspire others to do more work. Thanks.

 

[wahoowad]

This is what I have for my pieces of oak and hickory I have been tracking. The oak 'looks' seasoned and I would burn it. The hickory does not. Good thing this hickory is from my last pile to burn this year, assuming I get to that pile at all. I'm dying to pop them both open and check the moisture content, but I might keep weighing them instead.

 

[robmints]

Does Oak or other hardwood dry faster split?

 

[My_3_Girls]

wood F appears to have been the wettest and had the most rapid heat loss. It would have been burnable in 4 months. Contrast this to wood D that took a month longer to lose 15% less moisture.

This is part of the old "I tarp/don't tarp my piles because..." F is the dried piece from last year - It's already been dried past the fiber saturation point (FSP) of about 28% MC. At the FSP, all of the 'free' water is gone from the wood fiber, and the 'bound' water starts to leave. While rain water, melting snow and other short term exposure happens, the free water enters the fibers but does not become bound in the fibers. Free water moves much easier than bound, so this result shows that once block F dried, it will get rid of the free water more quickly than the fresh cut blocks. As far as the split vs. unsplit, water moves easier longitudinally than laterally thru wood fiber. More moisture comes out the ends vs. thru the sides - that's why we see bubbles on the ends more than on the faces of burning, wet wood (or when BB is out behind the woodshed with a bucket of soap and a dry piece of red oak).

I know, I know - when's he going to stop typing???????

 

[Gooserider]

Interesting data, and I think it's consistent with some of what we've already known about wood drying more out the ends than the sides, etc.

What I did get out of the data from eyballing it is that it looked to me like both the splits and the rounds took the same amount of time to reach a stable weight (presumably seasoned / burnable) the curves were shaped differently - The splits seemed to drop quite a bit initially, then slowly loose the remainder, while the rounds lost at a rate that was slower to start with, but stayed more consistent. This seems to agree with the suggestion that while most evaporation occurs out the ends, there is some early evaporation that occurs through the exposed split surfaces, but not through bark. Thus the splits lost more surface water at the start, but both splits and rounds take the same time to lose the "end water".

This would suggest to me that if getting a load of logs to process, the priority should be to cut it to stove length rather than splitting. Also that while it doesn't speed the process of reaching "optimum" dryness to split, it does get you to a "semi-burnable" state faster if you split - IOW, if you get your wood cut to stove length in April, it won't matter much when you split, but if you don't get it cut until late September, you will be in better shape at the start of burning season in November if you split than if you didn't. Again this mostly confirms what we've been saying to late starters all along - cut and split ASAP, and split it smaller than you might normally to get as dry as you can, albeit not ideal.

Thoughts for future research - there was recent discussion of a kid's Science Fair project - this might even be good for that (hint)

1. I think this study was good, but it was harder to interpret because we had data from different species of wood, that presumably came from different sources, and may have been at different moisture states at the start of the experiment (I think shown by the wide range of % weight changes). This gave us to many variables to deal with.

2. IMHO it would be better to start with a single log (which presumably should have a fairly uniform moisture) and cut it into rounds which were then split or not in order to make the sample peices. That way presumably all of the test samples would have about the same initial moisture, and should need to loose a similar
e of weight to reach the stable "seasoned" level. If the number of samples were large enough, it might even be possible to "sacrifice" a sample or two at regular intervals by splitting to determine an actual moisture reading.

3. This sort of test using multiple peices that are as close to "identical" as one can reasonably expect from a material like this might also be a good way to test some of the various "methods" of storing for drying - tight vs. loose stacking, uncovered vs. top-covered stacks vs wood sheds, top of stack vs. bottom, Holz-Hausen vs other, and so forth. The challenge might then be figuring a way to put the test logs in a "random" place in the pile that would still allow the retrieval of the sample for periodic measurments without requiring monthly re-work on the wood pile - presumably one might build a sort of "frame" out of other splits that the sample could be slid in and out of?

Gooserider

 

[fishboat]

If someone has a variety the wood types (I don't) & is willing cut various pieces to spec I could run a statistically designed experiment (DOE) that addresses Goose's suggestions and a few other parameters. The end result would be a quantiative model & subsequent plot or two that would illustrate (identify) the optimal conditions to dry wood (hard, soft, split, rounds...) DOE's can be a bit of work, but they do offer a good amount of quantitative info.

 

[Rhone]

This was really cool. I've been curious about the difference between bark up, and bark down if you plan on doing another test. I've theorized that bark up is faster and better drying. Since bark is nearly waterproof I believe it prevents rain from re-absorbing into the wood in rainy New England anyway. But, the main reason I believe bark up will dry faster is that it's darker than the almost white wood fibers of a fresh cut piece, and when sunlight strikes a darker surface more of it should be absorbed vs. reflected and warm up the wood piece more than if hitting light wood fibers. Sort of the same as, wearing a darker shirt in the sun will warm you more than wearing a light colored. Anyway, that's what I theorize that bark up is faster drying as it puts the dark side towards the sun and goes without saying only matters with piles in sunlight (and fresh piles, as the bark will eventually fall off).

 

[chainsawdad]

Very useful info! Guess I'll stop splitting those smallish 3"-4" logs, which I'd been doing to "help them dry" (which apparently it doesn't).

Anyone have any sense of how much a dead tree dries out before it's cut to log lenghts? I was assuming that the moisture would seep downward if the tree is still standing, and that at lest the top part would be reasonably dry and ready to burn, but I may be off base on that. I just moved to a place where I can cut my own wood recently, and there are a decent number of dead trees around, so I'm hoping it might be possible to get some more wood for this winter out of them.

 

[Gooserider]

"Standing deads" seem to be extremely variable in dryness - I've seen reports (often with isture numbers) ranging from "just as damp as green" to "ready to burn" or close to. Seems to be independent of tree species, climate, or time of year. If they've been dead long enough the bark is falling off, they tend to be drier, but not always, and may be "punky"... Only thing I've been able to come up with is to say drop them, cut em up, and see what you have for a moisture content...

Gooserider