Moisture Content Question

[Adamal]

I've got what I think is some Elm. The tree came down last year and I cut it up into 16" rounds early this year.

The reason I think it's Elm is because it's damn near impossible to split by hand (also, the leaves matched up pretty well). It's REALLY stringy and hard as a rock. I won't even attempt to hand split anything larger than 8"-10".

Anyway, I split some yesterday and the moisture content was 25%-34% on the fresh sides. Today, the same pieces are measuring 11%-14%. I'm sticking the probes in as far as they'll go too.

What's the story here? I'm fairly new to this so, I'm not sure which measurement I should go with... Or is it somewhere in between?

Thanks!

 

[JeffHK454]

I'm gonna step in for @Whitespider on this one.....hand held non-calibrated moisture meters are completely inconsistent and inaccurate !

 

[Whitespider]

*

 

[Erik B]

@Adamal It is the concensus around here that a MM should be used on a fresh split of wood. Your first readings may be more accurate than the second readings, if you are inclined to believe one of those meters.

 

[Marshy]

I agree, use it on a fresh split and don't put too much trust in them it's just an estimate.

 

[mohick]

Carefully lay the M M on the wood to be split, then hope like heck you can hit it dead center, best swing you will ever make !!!

 

[Whitespider]

Adamal,
Moisture meters work by measuring the electrical resistance (or, more correctly, conductance) between the two pins along the grain. Wood, even dry wood, will conduct some electricity... it's just not a very good conductor. However, the higher the moisture content of the wood, the better its conductance until it reaches a point, called the saturation point where conductance stops increasing. The rub is, the ratio of moisture content to conductance is not linear... adding x-amount of moisture does not equal x-amount of conductance, it varies with moisture content and species.

Keep in mind, when you use a moisture meter, you are only measuring the electrical conductance between the two pins... you are not measuring the entire piece of wood, and you are not measuring moisture content, the meter simply reads out a (supposed) moisture content based on the conductance measurement. The reason for the lower moisture reading (or higher electrical resistance, or decreased electrical conductance) the day after splitting is because the outer surface of the wood dries rapidly. And the less dense the wood is, the deeper that rapid drying over a given time period. And you're measuring the surface, and only between the two pins... not the entire piece of wood.

The moisture content of wood is stated as weight ratio... the ratio of moisture weight to dry wood weight. If you have a 30 pound piece of wood at 50% moisture content... it contains 10 pounds of moisture and 20 pounds of wood. In other words, the moisture weighs 50% of what the wood weighs without the moisture. If you have a 30 pound piece of wood at 100% moisture content... it contains 15 pounds of moisture and 15 pounds of wood. In other words, the moisture weighs 100% of what the wood weighs without the moisture. So, if you have two pieces of wood, one oak and the other elm, both measuring one cubic foot, and both at 25% moisture content the cubic foot piece of oak will contain a lot (a lot) more moisture than the cubic foot of elm, because the oak is much denser (heavier) than the elm.

Now understand, the electrical conductance, at any given moisture content, is not the same for different species of wood. Grain straightness, density, cell structure, deterioration over time, temperature, and many other things also effect electrical conductance. Meaning your moisture meter cannot possibly be accurate in all species of wood... or at all temperatures. Likely it is calibrated for dimensional lumber at 65°, pine and/or fir boards used for construction. Your moisture meter is a gadget... you can use it to make rough comparisons, but that's about it. Let's say you measure some wood in June at 28%, and then again the same wood in September at 17%; the most you can claim it the wood has lost some amount of moisture... but you cannot say with any confidence it has lost 11% (28-11=17) because the moisture-conductance ratio is not linear, is not the same per species of wood, and is effected by temperature. To get anything close to an accurate comparison, you would need to be able to calibrate your meter for species and temperature at each measurement (or know the temperature calibration and do the correction calculation).

Have fun with your moisture meter, it's a tool (or gadget) that many find useful... but it does not eliminate the need to use common sense, experience, and plain gut feeling when determining if your firewood is ready for the firebox. Personally, I don't own one... it really cannot tell me anything I don't already know using traditional guesstimating methods.
*

 

[mohick]

They tell us one thing spider. that there is a sucker born everyday that will spend money on toy junk!!!!!!!!

 

[muddstopper]

Here the way I look at Moisture Meters. I have a pile of wood for my stove. I need a fire to keep my house warm. Am I going to not use the wood because the MM says the moisture content is to high. I have two piles of wood to choose from to heat my house, am I going to test both piles to see which pile I should use this year, or do I just use the wood I cut last year and let the pile of wood I cut this year dry and use it next year. A little common sense here. Is having a MM going to change my decison as to which pile I use, not likely, am I going to let my house get cold because the MM says my wood is wetter than it should be, not likely. If a MM isnt going to change which wood pile I use or save me any money by not using a pile of wood that the meter says is wet. what is the purpose of even owning a MM. Waste of time and money. Is dry wood better for heating your house than wet wood, of course, but if the wood you have happens to be wet and its getting cold, are you going to let the wood set until next year so it can dry some more, or are you going to build a fire in your stove to stay warm and make a commitment to process your next years wood early enough so that next year your wood is dry when you need a fire.

 

[sledge&wedge]

Here the way I look at Moisture Meters. I have a pile of wood for my stove. I need a fire to keep my house warm. Am I going to not use the wood because the MM says the moisture content is to high. I have two piles of wood to choose from to heat my house, am I going to test both piles to see which pile I should use this year, or do I just use the wood I cut last year and let the pile of wood I cut this year dry and use it next year. A little common sense here. Is having a MM going to change my decison as to which pile I use, not likely, am I going to let my house get cold because the MM says my wood is wetter than it should be, not likely. If a MM isnt going to change which wood pile I use or save me any money by not using a pile of wood that the meter says is wet. what is the purpose of even owning a MM. Waste of time and money. Is dry wood better for heating your house than wet wood, of course, but if the wood you have happens to be wet and its getting cold, are you going to let the wood set until next year so it can dry some more, or are you going to build a fire in your stove to stay warm and make a commitment to process your next years wood early enough so that next year your wood is dry when you need a fire.

I'll start by saying I agree with you, and I don't rely on a moisture for anything other than my own information. Just to play devil's advocate, consider a situation where you have a pile of split oak from January 2015 and a pile of split beech from October of 2015 to choose from for your 2016 heating season... Assuming you check both types of wood with your meter at the time you split them, you could use your meter again to determine which has dried out more since you split. Maybe your read of 29% on the oak and 24% on the beech wouldn't be accurate as far as the actual moisture content, but if your previous oak read was 36% and your previous beech read was 46%, you could at least reassure yourself that even though the beech was cut later, it's still better seasoned and would be the better choice for 2016 burning... See what I mean?

Either way, I stack as I split, so I don't really have an option... Whatever went into the stacks first comes out of the stacks first.

 

[svk]

I've got what I think is some Elm. The tree came down last year and I cut it up into 16" rounds early this year.

The reason I think it's Elm is because it's damn near impossible to split by hand (also, the leaves matched up pretty well). It's REALLY stringy and hard as a rock. I won't even attempt to hand split anything larger than 8"-10".

Anyway, I split some yesterday and the moisture content was 25%-34% on the fresh sides. Today, the same pieces are measuring 11%-14%. I'm sticking the probes in as far as they'll go too.

What's the story here? I'm fairly new to this so, I'm not sure which measurement I should go with... Or is it somewhere in between?

Thanks!

The outside 1/4 inch of a split will dry very quickly but it will take months to get the entire split to reach equilibrium. Unless you resplit that piece and measure the middle of the fresh split it isn't an accurate measurement.

As others have said it's a relative test. I cut aspen that is over 45% MC when first split. I can judge how quickly it's drying by making a fresh split and retesting throughout the summer. Different species dry on different timelines and may not read exactly the same.

Also the cheap meters do not read accurately on frozen wood.

 

[Marshy]

Maybe a guy buys his wood and wants to know roughly how "seasoned" the delivered wood is. I think they are useful to determine if you're buying green wood or not. Again, IMO its just a gross reference to the moisture content.

 

[rarefish383]

While I read all of this, I think all of my wood dried out. So, I'm just going to start with the pile that is farthest away. Then when the snow gets here, what's left will be closer. Maybe I'll buy a MM nest year? Joe.

 

[muddstopper]

I'll start by saying I agree with you, and I don't rely on a moisture for anything other than my own information. Just to play devil's advocate, consider a situation where you have a pile of split oak from January 2015 and a pile of split beech from October of 2015 to choose from for your 2016 heating season... Assuming you check both types of wood with your meter at the time you split them, you could use your meter again to determine which has dried out more since you split. Maybe your read of 29% on the oak and 24% on the beech wouldn't be accurate as far as the actual moisture content, but if your previous oak read was 36% and your previous beech read was 46%, you could at least reassure yourself that even though the beech was cut later, it's still better seasoned and would be the better choice for 2016 burning... See what I mean?

Either way, I stack as I split, so I don't really have an option... Whatever went into the stacks first comes out of the stacks first.

Your example is meaningless to the way I process my wood and misses the point I was making about burning what you have or not burning because your MM says the wood is not seasoned. First, I get very little beech wood, while there is some here, it makes up a very small percentage of my forest. I do have a very large mix of different hardwoods to chooses from. Not all wood dries at the same rate but that makes very little difference in the wood I get to burn this winter. If I get a load of mixed wood, it all gets bucked at the same time and split and stacked at the same time, therefore my stacks will have as varied a species of wood as the wood that I harvest. I am not going to separate wood by species and I will burn the wood as it comes off the stacks. Now if I only have one stack of wood to burn, I have to decide do I burn it regardless of moisture content, or do I check with a MM and turn up the furnace until the wood is dry enough to be deemed burnable in my wood stove.

 

[user 122190]

I'm splitting logs that have been out in the summer heat 3 seasons. still some are dry and can almost be split with a hatchet, while some are a PITA, and still ooze oils. IMO, do the best you can to burn as much well seasoned wood as you can, and you won't be bothered by some creosote from others that defied drying out completely.

 

[svk]

I'm splitting logs that have been out in the summer heat 3 seasons. still some are dry and can almost be split with a hatchet, while some are a PITA, and still ooze oils. IMO, do the best you can to burn as much well seasoned wood as you can, and you won't be bothered by some creosote from others that defied drying out completely.

Agree with this.

I rarely let my rounds sit more than a few months but did leave some big aspen and balsam rounds in full sun for 2 years and they were ready to burn when split.

 

[sledge&wedge]

Your example is meaningless to the way I process my wood and misses the point I was making about burning what you have or not burning because your MM says the wood is not seasoned. First, I get very little beech wood, while there is some here, it makes up a very small percentage of my forest. I do have a very large mix of different hardwoods to chooses from. Not all wood dries at the same rate but that makes very little difference in the wood I get to burn this winter. If I get a load of mixed wood, it all gets bucked at the same time and split and stacked at the same time, therefore my stacks will have as varied a species of wood as the wood that I harvest. I am not going to separate wood by species and I will burn the wood as it comes off the stacks. Now if I only have one stack of wood to burn, I have to decide do I burn it regardless of moisture content, or do I check with a MM and turn up the furnace until the wood is dry enough to be deemed burnable in my wood stove.

I didn't miss your point, I agreed with it. However, you definitely missed mine. Oh well, no harm no foul. You mentioned my example is meaningless to the way you process wood, which is what I said as well... First in, first out, regardless of moisture meter readings. Either way, no sense in carrying on.

 

[lknchoppers]

I have a moisture meter and I get to use it quite a bit. If you know how to use it, and measure the wettest part of the wood on a fresh split, you can get a handle on how dry the wood is and if it's ready to burn. I carry a splitting hatchet and a moisture meter when I buy wood, bang the wood together and listen, probe it with the meter and look at the wood. Mistakes cost me money so I like to have several methods to characterize the firewood I buy. So far I haven't seen a piece of wood that looks "Wet" and measures dry or burns good. I also pull wood from different spots in the pile to see how much it varies.

 

[muddstopper]

I didn't miss your point, I agreed with it. However, you definitely missed mine. Oh well, no harm no foul. You mentioned my example is meaningless to the way you process wood, which is what I said as well... First in, first out, regardless of moisture meter readings. Either way, no sense in carrying on.

Dont you just hate that, when you are agreeing with someone and they dont seem to realize it. I'll try to read a little more carefully next time.

 

[CaseyForrest]

Such angst over a moisture meter.......