Moisture Content. (Once more with feeling)

[Sloken]

Would someone straighten me out on this. ??? (I think my line of reasoning got warped in the kiln)  Is moisture content of say 30 percent mean that 30 percent of the weight is moisture? Or is it as one person stated a moisture content of 100 percent means half the weight is wood and half is water?  Appears to me if I stick something thats 100 percent water in the kiln I won't see a whole lot of product once its dried.
Sloken

[Ianab]

Hi Sloken

Yes it's easy to get confused on that one.
The moisture content is a % of the totally dry ( in an oven ) weight.
So if you have 100 kilograms (dry weight) of wood, containing and extra 100 kilograms of water, thats 100% mc. At 30 % it's 100 kg of wood with 30 kg of water. etc. When it's dry and at 8 % it will be 108kgs.

Clear as mud?

Cheers

Ian

[Den Socling]

and so 100% MC means 50% of the total weight is water

[Sloken]

Thanks fella's.  Think I understand now.  The moisture content figure is referenced to the wood being completly dry, not to its present weight when the reading was taken.  You see now where the "Slo" part got put in front of my name.  :D
Ken

[Paschale]

Hmm...then that begs the question...what's the moisture content of those sunken logs, that are really waterlogged?  150%?   :D

[Paschale]

Actually, now I'm really curious.  I suppose there's a "critcal mass" that is reached at some point, where a log just can't hold anymore water.  I suppose it depends on the species, and the size of the cell walls, etc.  Anyone ever calculate that sort of thing?  Just more out of trivia than anything else...

[kilndry]

And so, it looks like this:


%mc = green weight - oven dry weight    x100
                                      oven dry weight

In theory, the green mc is thus unlimited, but obviously each log/board would have a maximum volume it could hold.

[beenthere]

Good discussion. What can be confusing is that some engineering types (some materials other than wood) like to divide the wet - dry difference by the wet weight. That formula doesn't work well for wood, but sometimes creeps into the literature and the discussion of wood moisture content. Wierd wood moisture contents can come out if using this 'method'.

Follow Kilndry and Den's thoughts and you will be accurate for wood.