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how long to wait for wood to "air out"?

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  • how long to wait for wood to "air out"?

    Hi all,

    Yesterday I bought a bunch of spruce 8-foot 2x4's and planks to build some rough shelves for my garage. The wood had been sitting out in the open in the lumber yard.

    Last time I did this, I put the wood in my garage, waited two days to let the wood "air out" a bit and hopefully get rid of moisture stored up in it, and then built some shelves. Within a month later, the shelves were bending out and warping.

    Is there some agreed-upon time that spruce wood should be left to sit before it's used to build something, in order to keep it from warping after a short period of time? I'm relatively new to woodworking.

    Thanks!
    Dave

  • #2
    Re: how long to wait for wood to "air out"?

    Many time construction grade lumber is dryed to what is called S Dry, or that means the lumber was surfaced when the timber is down to 19%,
    there is still considerable drying to take place yet,
    the two urls have a little info on "S-DRY" lumber, http://www.kentinternational.ca/broc...er_Grading.pdf

    http://www.umass.edu/bmatwt/publicat...wood_myth.html

    If your air drying lumber the rule of thumb is a year of inch of thickness, for raw green lumber, but at 19% your down considerably, depending on the humidity if inside and depending on location 5% to 12% is about the best one can do,
    (just tested a piece of oak flooring I have here in my office and it was at 6% no finish on it, but has been here for nearly a year).

    Spot check the lumber you are using with a moisture meter. It is important to match the MC of the wood you are using with the equilibrium conditions it will see in service. The in-service MC or equilibrium moisture content (EMC), can be benchmarked to relative humidity:

    • RH 25% ~ MC 5%

    • RH 50% ~ MC 9%

    • RH 75% ~ MC 14%

    • RH 90% ~ MC 20%

    http://www.umass.edu/bmatwt/publicat...wood_myth.html
    the best bet is to invest in a wood moisture meter, (on e bay some times one can pick up one for about $25), new they start in about $100, that way one can know what the moisture content of the lumber your installing is, and how much more drying will or needs to take place.
    Last edited by BHD; 09-18-2008, 12:27 PM.
    Push sticks/blocks Save Fingers
    ~~~~~~~~~~~~~~~~~~~
    "The true measure of a man is how he treats someone who can do him absolutely no good."
    attributed to Samuel Johnson
    ~~~~~~~~~~~~~~~~~~~
    PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

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    • #3
      Re: how long to wait for wood to "air out"?

      Oh, no...the URL you posted talked about the wood's moisture content and said that if the wood's been stored outside in wet weather (like the stuff I bought), its MC can skyrocket.....does that mean that I have to wait months, or a year, to make some garage shelves??? Surely that can't be what that means....

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      • #4
        Re: how long to wait for wood to "air out"?

        normally even if wood gets wet from rain or what ever it normally does not soak in to the entire board normally just the surface is wet, and normally once a board has been dry-ed once it will re dry much faster, the cells are all ready broke down, and seem to release there moisture much faster the second time around, in my experience

        I would let set for two weeks inside to acclimating , if possible, longer if you have the time, if you have an attic in the shop or garage where the temps are a little higher that helps,

        another fair site for some basic information,
        http://www.lowes.com/lowes/lkn?actio...StrtWWood.html

        hard woods are usually dry down to about 10% or a little less.
        Last edited by BHD; 09-18-2008, 12:46 PM.
        Push sticks/blocks Save Fingers
        ~~~~~~~~~~~~~~~~~~~
        "The true measure of a man is how he treats someone who can do him absolutely no good."
        attributed to Samuel Johnson
        ~~~~~~~~~~~~~~~~~~~
        PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

        Comment


        • #5
          Re: how long to wait for wood to "air out"?

          Awesome....thanks BHD for the very helpful info and links.

          Comment


          • #6
            Re: how long to wait for wood to "air out"?

            From personal experience: Even pressure treated pine/spruce, etc bought from the Borg that is soaking wet will stabilize pretty much in about 2 - 6 weeks if kept in your garage (i.e. sheltered and out of the sun). [PT KDAT (kiln dried after treatment) is still about 19% MC, but will stabilize in about 2 weeks. That means its down to about 12%) However, to minimize warpage, it helps to keep it "stickered" and strapped. By that I mean putting 1 x 1 or 3/4 x 3/4 sticks between the boards, with each stick exactly under the one above, separating the boards, and then a couple of cargo straps around the whole pile to keep it straight. Put 4 x 4s under the stack and wrap the straps around the 4 x 4s. Putting it where the air can move around it will greatly speed the drying but keep it out of direct sun and rain.

            If you are going to split it or resaw to a thinner width/thickness, go for the six weeks, do the split or resaw and re-stack/sticker for another six. Put the sawn faces to the sticks.

            Soft woods like pine. spruce, and fir dry pretty quickly compared to hard woods like walnut. oak and maple. Raw off the tree pine 2" thick will dry out in about 6-9 months. Black walnut of the same thickness may take 2 years. Oak about 18 months, but if raw will likely split on the outside due to its high (35%+) original moisture content. Harder the wood, longer the air-dry time.

            Beings you are up in Canada, the cooler weather will help in eliminating splitting/checking, but will increase the stabilization time unless the relative humidity is low.

            Realize that just drying the wood will not take the stress out of it. A thick board, even if air dried to 7%, may still have a lot of stress in it if it grew on a hill, subject to a lot of wind, etc. When you resaw/split it, that stress will exert itself, so the wood may still move. When cross-cutting, I have had kiln-dried white oak boards split on one side of the cross cut and not on the other just because of the internal stress. This is less a problem in softer woods, but illustrates that there are no guarantess working with wood.

            JMTCW

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            Practicing at practical wood working

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