American elm, fresh-cut to 20% in 103 days

[Jon1270]

Back in early March a neighbor had a small elm taken down, and I took the opportunity to conduct a drying experiment. I oven-dried a sample slice, weighing it before and after, and established the initial moisture content at 76%. I also weighed a medium-sized split, and have continued weighing it every week or so, regularly calculating the average moisture content. Today that split of elm hit 20%.



This method is much more accurate than an electronic meter, but the result probably isn't typical; the split was sitting on top of a stack in a very sunny spot, only about three feet from a SE-facing brick wall that holds a lot of heat. Also, 20% is the average moisture content. It may be 10% on the outside and 27% in the middle, but overall it's 20%. For comparison I'm also tracking the drying of one split each of red oak, white oak and mulberry. None of those is ready to burn quite yet.

 

[Paulywalnut]

That is a nice comparison. I'll bet the red oak loses by a year or two.

 

[Macpolski]

Good work on the analysis. I am quite anxious to see the graphs of the red and white oak.

 

[Jon1270]

I'll bet the red oak loses by a year or two.

That's what I expect too, but it's been surprising how fast the oaks have lost moisture early in the process. The red oak dropped from 79% to 34% in 70 days, and the white oak went from 80% to 37% in just 47 days. The mulberry was wetter to start with (88%) and actually lost moisture a bit slower than the oaks, reaching 32% in 120 days. But the oaks' drying seems to be slowing while the mulberry keeps chugging down. I'm curious how the trends will look by the time the weather starts cooling off in the fall.

When I got the white oak, I put about a half a face cord of it in the rafters of my garage just to see what happens when the wood is kept warm (sun beats on the roof for several hours a day) but completely sheltered from both sun and breezes. That wood seems to be drying very quickly, but I neglected to weigh any of those splits so I can't get an accurate measurement.

 

[Woody Stover]

But the oaks' drying seems to be slowing while the mulberry keeps chugging down

Yeah, seems like the Oak slows to a crawl in the lower 20s.

 

[TimJ]

Hey I might go back to cutting my wood in the summer to be ready for the fall

 

[bogydave]

Good study. Great for your location to know average moisture loss of various woods.

Be nice to track the same wood , splits in varies stack locations,
top, bottom, middle , north facing south facing..
Been gonna do that, some day
Track local weather, relative humidity, precip..

What type of scale do you use?

 

[Jon1270]

Be nice to track the same wood , splits in varies stack locations, top, bottom, middle , north facing south facing.. Been gonna do that, some day Track local weather, relative humidity, precip..

Yeah, there are an awful lot of variables. The more carefully I look at this, the fewer generalizations I feel like making.

What type of scale do you use?

Just a ~$20 digital kitchen scale that reads in grams and can handle up to 5kg (about 11 lbs).

 

[bogydave]

You mean I have to be able to convert kilo-grams to pounds

 

[Backwoods Savage]

Back in early March a neighbor had a small elm taken down, and I took the opportunity to conduct a drying experiment. I oven-dried a sample slice, weighing it before and after, and established the initial moisture content at 76%. I also weighed a medium-sized split, and have continued weighing it every week or so, regularly calculating the average moisture content. Today that split of elm hit 20%.

This method is much more accurate than an electronic meter, but the result probably isn't typical; the split was sitting on top of a stack in a very sunny spot, only about three feet from a SE-facing brick wall that holds a lot of heat. Also, 20% is the average moisture content. It may be 10% on the outside and 27% in the middle, but overall it's 20%. For comparison I'm also tracking the drying of one split each of red oak, white oak and mulberry. None of those is ready to burn quite yet.

Nice to see experimenting.

Jon, I understand where you are coming from and you are trying to get an average. However, the number that counts is that number you get on the inside. That wood is still at 27% for all intents and purposes. That 10% on the outside is a number that should not come into the calculation. So I would say your wood is at 27% and not at the 20% you are stating.

 

[osagebow]

When I got the white oak, I put about a half a face cord of it in the rafters of my garage just to see what happens when the wood is kept warm (sun beats on the roof for several hours a day) but completely sheltered from both sun and breezes. That wood seems to be drying very quickly, but I neglected to weigh any of those splits so I can't get an accurate measurement.

That's similar to how i get reduced bow staves from 15% - 20% or so down to 7%-8 % to finish them up. I put them in a hot attic for a few weeks. Wood is only a few inches thick though.


Cool study you got going on!

 

[Apprentice_GM]

Hey Jon1270,

Nice work, I'm a fan of these types of studies, especially with accurate measuring technique. I did one a while ago comparing Holz Hausens to ricks but didn't oven-dry to establish starting MC accurately or measure constantly through the process, just before and after results with different splits in different locations.

What weight and rough dimensions is the split?

What happened just prior to June 11th? Did it rain? (The graph upturn in MC)

Good study. Great for your location to know average moisture loss of various woods.

Be nice to track the same wood , splits in varies stack locations,
top, bottom, middle , north facing south facing..
Been gonna do that, some day
Track local weather, relative humidity, precip..

You mean like this?
Holz Hausen Experiment - Results are IN!!

 

[Jon1270]

Jon, I understand where you are coming from and you are trying to get an average. However, the number that counts is that number you get on the inside. That wood is still at 27% for all intents and purposes. That 10% on the outside is a number that should not come into the calculation. So I would say your wood is at 27% and not at the 20% you are stating.

Sorry, but you're wrong on this one Dennis. (Am I still alive!?) The 20% is correct, meaning that the weight of the water remaining in the wood is 20% of what the wood would weigh if it were oven-dried to remove all moisture. Of course there's a gradient, wetter in the middle than on the outside. The average MC is, well, the average. The 27%/10% numbers I threw out were just a guesses; I haven't actually split the thing open and metered an interior surface, because doing so would prevent me from meaningfully tracking further drying.

What weight and rough dimensions is the split? What happened just prior to June 11th? Did it rain? (The graph upturn in MC)

The elm is a triangular split maybe 4" on a side and about 14" long. Initial weight was 3718g, and yesterday evening when it hit 20% it was at 2542g.

Yes, the leveling off starting around the beginning of may, and the subsequent zig-zags, are periods of rain and dry weather. It's been a wet spring.

 

[bogydave]

We had a member a year or so ago that did science on wood.
measured all kinds of stuff.
Maybe you'll become the site's
"Wood Guru" with the scientific facts.

Keep us posted on you & your wood's progress!

Nice graph !
Excel?

 

[paul bunion]

You should read up on air drying lumber if you have not, a lot of science done there. Stacking, spacing, airflow, time etc. Not exactly firewood but similar. The differences between 4/4 boards and 8/4 boards (3 times as long) illustrate variations in drying times dependent on size and a lot of other tidbits that carry over to firewood.


Cliff Notes versions of below 2 ==> http://extension.missouri.edu/p/G5550
Long ==> http://www.extension.iastate.edu/forestry/publications/pdf_files/fpl-gtr-117.pdf
Charts ==> (broken link removed)

 

[Jon1270]

You should read up on air drying lumber if you have not, a lot of science done there.

Yep, I actually have longer experience with lumber than with firewood. Somewhere around here I've got a copy of an old Fine Woodworking book called 'Wood and How To Dry It," a compilation of magazine articles detailing various approaches. The big difference is that lumber becomes almost worthless if it cracks or stains, so lumber drying has to be managed and controlled a lot more carefully.

Nice graph ! Excel?

Yep. Excel will practically do that by itself.

 

[Jon1270]

One of the inherent challenges with my little comparison study is that the various trees weren't cut at the same time. Temperatures warmed considerably between the time the mulberry was cut (late February) and when the oak came down (early May). The best I can do is apply the rule of thumb that says wood dries twice as fast for every 20 degree (F) increase, so that a day in June counts for more "drying time" than a day in March, similar to the math I used here.

Doing that, the comparison so far looks like this:

 

[Applesister]

So Jon, if you have a woodworking background, why did it take you longer to become a wood burner?
Marriage? a new house that used wood heat? cost of fossel fuels? embracing a lifestyle?
Your scientific approach is your 'signature' or stamp.
I was snooping in the Gear forum and was amazed at the chainsaw buffs. Techy stuff there. I dont think its derailment to wonder at the wondering. Im just wondering....

 

[Jon1270]

why did it take you longer to become a wood burner?

Lack of exposure to it, mostly. I come from a family of suburbanites that hadn't burned wood outside of a campsite for at least 2 generations. Also our last house was tiny and there was no place near the chimney to put a stove. But at that same house we had to take down a bunch of dead ash trees, and I gave away the wood because that was cheaper than having the tree service take it. One of the guys who answered my Craigslist 'free firewood' ad was the first person I ever talked to in depth about woodburning, and he talked like a typical Hearth.com member -- all about his moisture meter, how many years of wood he had on hand, showing me pics of his stacks on his smart phone. That conversation sparked my interest. Then we moved to a house with an actual fireplace, and suddenly wood burning became possible.

 

[Augie]

The best I can do is apply the rule of thumb that says wood dries twice as fast for every 20 degree (F) increase, so that a day in June counts for more "drying time" than a day in March, similar to the math I used here.

Basic Idea Behind solar kilns. Oak can be ready to go in 90 days..... I have one rigged up with little more than a 10x20 black plastic tarp.(broken link removed to http://sbio.vt.edu/about/extension/vtsolar_kiln/)
We shall see how it works there is about 2 face cords of Oak that was heavy when I put it up

 

[Backwoods Savage]

Sorry, but you're wrong on this one Dennis. (Am I still alive!?) The 20% is correct, meaning that the weight of the water remaining in the wood is 20% of what the wood would weigh if it were oven-dried to remove all moisture. Of course there's a gradient, wetter in the middle than on the outside. The average MC is, well, the average. The 27%/10% numbers I threw out were just a guesses; I haven't actually split the thing open and metered an interior surface, because doing so would prevent me from meaningfully tracking further drying.


The elm is a triangular split maybe 4" on a side and about 14" long. Initial weight was 3718g, and yesterday evening when it hit 20% it was at 2542g.

Yes, the leveling off starting around the beginning of may, and the subsequent zig-zags, are periods of rain and dry weather. It's been a wet spring.

No problem Jon as I am wrong lots of times. However, what really counts is what the high moisture content is. The fire doesn't know the average and that is why when we test wood, we test the inside of the log and not the outside. The factor that means the most is what the inside of that log is. Over 20% sucks and that means your 27% wood is not yet ready.

However, all is unimportant anyway as now you state that the figures were guesses. In addition, you have not actually split it open... But keep on experimenting as that is good. We all can learn.

 

[Jon1270]

The factor that means the most is what the inside of that log is. Over 20% sucks...

Yeah, it may well be that an overall average 20% MC is higher than ideal. 20% is the target number cited almost everywhere, but the standard method of using an electronic meter on a fresh-split surface errs high in most cases, because it takes the measurement in what is likely the wettest part of the wood.

 

[Backwoods Savage]

Yup. There is a reason for doing that. For me, I'll still take 3 years in the stack and forget all about moisture content. Wood burns wonderfully.