REHYDRATION OF KILN DRYED LUMBER

[Tony]

      Howdy all, going to cut down a large red oak this week. I'm going to bypass   the crosstie yard this time  and go for the hobby woodworker.  :

    1.  If and when I can find a local kiln to dry the lumber, then store it in the shop, how much will it rehydrate??  ??? ??? ??? (my shop is not insulated)

    2.  What would be the best length to cut the logs\lumber to market to the hobby guys??    ??? ??? ???

                                       Thanks, Tony  8)

[metalspinner]

Woodworkers can use lumber as short as three feet.  Now that is a pain to handle for you, but six footers can work.  I've only built one thing eight foot long.  That is the kitchen table.  If you find some nice clear boards together in the log, keep them together to sell as a table top.  If those boards are quartersawn, 8/4 is how I would cut them.  Craftsman style table tops are often thick  and having bookmatched boards for the top is a real treat that is hard to find.

[Riles]

Rehydrate would be the right word. Over the course of your Mississippi summer, 8% kiln dried lumber would take on water to go back up to about 12% MC. It pays to acclimate your lumber when building anything (or plan for the movement), not just for flooring.

[solodan]

I have often wondered about this, and makes me wonder why you would take it all the way down to 6-8% if it is going to go back up to 12%. ???

[beenthere]

solodan
You are right, not much point in dat. But the lumber doesn't swell all the way back to the 12% size it was. (called hysterisis).
However, if one pays for the drying to 6-8%, then seems a good plan to keep the relative humidity at the right level to hold it in a dry state. Or just dry it to the RH of storage planned.

[BBTom]

Let me see if I can answer your question.  Need to know that there are two types of moisture in lumber,  free water and bound water. 

free water is much easier to remove.  Bound water is held within the cell walls and is much harder to remove.

Kiln drying down to 6-8% leaves only that much bound water in the lumber.  When lumber rehydrates, it rehydrates with free water. 

A couple weeks in a heated shop will remove the free water that the board rehydrated with.  It would take a couple years in the same shop to remove that much bound water.

That is the reason we kiln dry.  So the furniture we build will not tear itself apart a year or two after it is in the home, when the bound water is finally removed.

[Don_Lewis]

Lumber will give up or pick up moisture from the air until it is equilibrium with the air. If you are building furniture, you generally want the joints to stay tight in the winter when the humidity in a heated house is low. This is a bigger problem in the North than the South but it is still a concern everywhere. Also, lumber machines and glues better when it is the right moisture content.

Once it is dried to between 6-8%, you can keep it there by keeping it in heated space. In Alabama in the middle of the summer, that space is going to be fairly warm. The rule of thumb is that the space where the wood is stored is kept 20 degrees (F) above the morning low temperature. If that is done, it will stay dry indefinitely.

[beenthere]

BBTom
I think your 'answer' about free water being picked up raises more questions than it answers. 

Send us some source for that conclusion, as I don't quite get how wood rehydrates with free water. If it did, then the cell walls wouldn't swell and wood wouldn't expand when stored in high humidity conditions.  So I'm thinking the bound water in the cell walls is what increases, causing swelling.

[Tony]

    Another question, will the PPBs infest kiln dryed lumber whether dewatered or rewatered ??  ??? ??? :   This is also a huge concern when marketing.

                                                                THANKS AGAIN, Tony  8)

                                                     

[BBTom]

Beenthere,

My education was gleaned from the Dry Kiln Operators Manual, Drying Hardwood Lumber and from the class I took on Kiln Drying at the NHLA. 

I did not go back and check for the specific answer, but just wrote what was in my mind about it, so maybe I am mistaken.

Tony,

I have seen PPB infest rewet lumber.