Theoretical drying/seasoning cordwood question

[cessna]

When    2.5mtr + /- lengths of cordwood are seasoning  by natural airflow or  kiln airflow  ,does the moisture want to escape from the length  of cordwood ,if the air temperature and humidity of the air  are higher than that of the cordwood  that one is drying/seasoning?

 

[openspaceman]

11 hours ago, cessna said:

When    2.5mtr + /- lengths of cordwood are seasoning  by natural airflow or  kiln airflow  ,does the moisture want to escape from the length  of cordwood ,if the air temperature and humidity of the air  are higher than that of the cordwood  that one is drying/seasoning?

 

There are a number of things that limit how moisture leaves a log, one is the distance it has to move through the log, while a log loses most through its ends a split log can lose it through the sides. Bark is near vapour proof so a long length with bark intact means the water all has to move to the end and then evaporate, severely limiting how fast it can dry. In the limit with something like birch  rotting will take place and as the end products of decaying wood are water and carbon dioxide the water content of the remainder is maintaining conditions for decay.

 

Another  limit is the moisture saturation (relative humidity) of the surrounding air, cold damp air doesn't absorb much moisture. If you heat air its relative humidity goes down and it can absorb more moisture, the higher temperature air also transfers heat to the log which increases the speed with which moisture can reach a surface.

[Ontario Firewood Resource]

If the air is more most than the wood, the water can't escape. Its like having a bottle of water in a full bathtub and opening the bottle to let the water out. Obviously it cant get out because its already in water.

[Stubby]

2 hours ago, Ontario Firewood Resource said:

If the air is more most than the wood, the water can't escape. Its like having a bottle of water in a full bathtub and opening the bottle to let the water out. Obviously it cant get out because its already in water.

Also you can dry wood down to , say , 15% or less moisture in the summer and when you get to winter and the rain and snow comes the wood will draw back some moisture from the now humid air and you might end up with 22% or 25% coz of the ambient conditions .  This is wood in the log store , covered with air flow .

[openspaceman]

1 hour ago, Stubby said:

Also you can dry wood down to , say , 15% or less moisture in the summer and when you get to winter and the rain and snow comes the wood will draw back some moisture from the now humid air and you might end up with 22% or 25% coz of the ambient conditions .  This is wood in the log store , covered with air flow .

Prove it.

 

In fact I find some bits will dry down to 10% in the summer, then slowly increase in weight, but I don't think in sunny Surrey they will get above 20% again.

[s.varty]

2 hours ago, Stubby said:

Also you can dry wood down to , say , 15% or less moisture in the summer and when you get to winter and the rain and snow comes the wood will draw back some moisture from the now humid air and you might end up with 22% or 25% coz of the ambient conditions .  This is wood in the log store , covered with air flow .

spot on mate, which is why buying premium kiln dried logs is pointless as opposed to cheaper air dried, unless of course if your planning on keeping your logs in a working kiln

[Stubby]

2 hours ago, openspaceman said:

Prove it.

 

 

I can't . Its  just what I think .  Do you disagree that logs will take up moisture from the air if the relative humidity is greater than the log itself ?

[openspaceman]

27 minutes ago, Stubby said:

 Do you disagree that logs will take up moisture from the air if the relative humidity is greater than the log itself ?

The relative humidity of the air is related to the equilibrium moisture content of the log but there is a time period over which this equilibrium is established, it would take an experiment  to see how this affects a log as we in the SE England are in a bit of a rain shadow so the humidity is often below 90% RH , which is a drying condition, albeit  very slight in the winter. Also re hydrating slightly lags drying at the same RH.

 

Also consider what we have been discussing about moisture meters,  I suspect the tables one sees about RH, temperature and moisture content are based on moisture content on a dry weight basis and even in a wet place, like Dartmoor a 90% RH gives  an equilibrium moisture content of <20% dwb which is between 16&17% on a wet basis.

 

Of course you are nearer the sea than I so probably a bit more humid.

[Ontario Firewood Resource]

2 hours ago, Stubby said:

I can't . Its  just what I think .  Do you disagree that logs will take up moisture from the air if the relative humidity is greater than the log itself ?

I wouldnt be surprised if the wood takes on moisture. It just seemed logical to think that moisture in the air permeates into many things in the area where it is moist. When I wrote that last sentence, it sounds reaffirming when you think about how many things or materials youve noticed change consistency in moist environments. Factors beyond moisture do the same too, just like how plastic is more brittle in freezing temps. Not the same but I'm generalizing effects of different atmospheric conditions. In an extreme example, if you had a kiln-dried log and put it into an extremely moist environment, it would have whatever amount of moisture in it afterwards. One more thing, if the moisture can get out, it can get in

[Stubby]

8 hours ago, openspaceman said:

 

 

Of course you are nearer the sea than I so probably a bit more humid.

I would take a serious high tide to reach the foot of the South Downs but yea I suppose .