What is seasoned?

[openspaceman]

Someone pointed me to this Wood Equilibrium Moisture Content Calculator from Wood Workers Source.com in another thread.

 

If you live in the moist northern hills and are getting 20% you are not doing too bad!

 

I'm glad you found that, I think the equilibrium mc in my house is about 17% on a wet weight basis, the sawn timber trade often calculates on a dry weight basis and for wet wood there's a lot of difference.

 

The equilibrium mc is dealing with the water bound to cell walls and there is a small amount of energy in the bonding, so the emc is slightly different as a log gains moisture from when it loses moisture.

 

Essentially the free cell water is fairly easy to remove and the wood doesn't change much as it evaporates, the cell wall water loss causes the wood to shrink, mostly tangentially, less radially and little lengthwise. It's controlling this latter water loss that seasoning planks is all about, making sure moisture leaves the surface at exactly the same rate it can migrate from the inside. This is not an issue with firewood where a few extra fissures speed up the drying.

 

With hardwoods the point where the free cell water is gone can be demonstrated by blowing or sucking through the grain. I would consider wood with the free water gone to be seasoned for firewood.

 

I'd also caution reliance on hammer in probes as a good measure of mc of drying, as opposed to stable, wood because in summer the wood surface will dry much faster than the moisture can migrate from the middle. A quick test is to cut a bit from the middle and gently microwave it on a defrost cycle, weighing before during and after. A point will be reached just before pyrolysis starts in the middle which is the oven dry weight, subtracting this from the wet weight gives the water content. If you over do it you will not be able to use the microwave for cooking again

 

To do it properly the sample needs oven drying at 120C for 24 hours. Any more than this an volatile organic compounds will be lost, reducing the dry mass.

 

AJH

[Tom D]

I think there is a lot of guff talked n this subject, as big j says the flue temperature is the important factor, dry logs contain MORE tar by weight than wet ones, so smouldering dry logs will gum up a flue just the same as wet ones. Dry timber burns hotter and therefore warms up the flue quicker allowing tar vapour to escape the top of the chimney, also it gives out more heat to the room as less heat is wasted boiling off the moisture in the wood.

 

i think you will struggle to get lower than 20%mc drying outside and another factor is species, split pop will dry much quicker than split cherry, so if they are both in the same pile some logs will be dryer than others, I don't bother to measure the mc of my logs any more, lives too short. There are loads of guys selling green wood out there.... and very few selling sub 20%mc stuff. Mine will easily pass the pepsi challenge with most of the stuff around here. And thats all that matters, its about making money after all.

[Dean Lofthouse]

I thought tar was transported up the flue in the moisture vapour and the vapour condensed on the cold liner and depositing the tar. If there's no moisture in the wood the tar is burnt and not transported. But there is always moisture in wood so the less there is the less tar deposits there are, also if the liner is hot, the water vapour cannot condense

 

 

Sent from my iPhone cos it was

[Nick B]

Most of my wood is around the 20 - 25% I would sooner not sell the wood if higher

[skyhuck]

Never risked that, the saying was fell on Xmas Eve, transport on Xmas day and mill on Boxing day.

 

Oak was often felled in late winter, left at stump and extracted after the hay harvest and then milled in the Autumn so that initial drying in the stick was not too fast.

 

AJH

 

I was talking about trees that had to be felled in summer , trees that are being removed to make room for development etc, but which are of furniture grade.

[Tom D]

The tar isn't soluble in water Dean, it will readily burn though if there is enough air,hence stoves recommending that they are burned full bore after each re-fuelling,to burn off all the tar. It is vaporised tar that gives the flames, once the tar is gone you're left with carbon which glows rather than flames.

 

Water can not pass 100 degrees until all of it has been turned into a gas, so a wet log will stay at 100 deg until all the moisture is gone. The boiling point of tar is much higher and theoretically won't be reached until all the water is gone, (in reality the edge of the log will be burning while the centre is still cold) and so as the wet log burns the moisture and tar is slowly released and the flue stays cold, with a dry log the log gets hot quickly boiling the tar more quickly too.

 

The flue needs to be above the condensation point of the tar for its full length in order for all the tar vapour to pass right out of the top, dry wood will make this easier to achieve.

[Johny Walker]

checked these the other day,i dont think ther going any lower with the amount a damp in the air ,

[openspaceman]

I was talking about trees that had to be felled in summer , trees that are being removed to make room for development etc, but which are of furniture grade.

 

Sorry I missed that point.

 

BTW felling trees in leaf in order to cause water loss is known as sour felling.

 

AJH

[Tom D]

Just googled this up..... there's a lot of chemicals in wood!

http://burningissues.org/pdfs/tablewoodsmokeweightnov02%20.pdf

[StephF]

I was told some time ago by a proper old-timer that the trees they used tu cut were always felled in late spring/early summer and then left for a month or so before snedding and processing further.

 

The reasoning was that the trees in full leaf would desperately try and stay alive and pulled much of the moisture out of the wood as they were just in full leaf. They'd then cut them after the leaves had died off.

 

I don't know how much moisture would be removed but I'd guess a fair bit?

 

Anyone tried this?

(sorry for the derail)

 

Worked with a french guy a few weeks ago, he told us where he came from, a bark remover is used late spring to ring bark trees destined for firewood (thinnings I presumed), and then the tree is left to die and season on the stump,(at least 1-2 years I think), when felled it is ready to split and burn, would save a lot of problems with storage space needed to dry out stacks of timber.

Anyone heard of this?