Green Lumber Compared to Kiln Dried Lumber: Which Kind Do You Need?

Forestry, done well, is a combination of science and nature which results in strong, durable wood. However, all wood species are harvested in the “green” condition, which is a term for the properties which behold wood in the wild.

There’s Green Wood

Freshly Cut TreeMany observers would be shocked at the high (“green”) moisture content (MC) of some wood species. Since trees comprise an autonomous eco-system of water and nutrients, it stands to reason that sapwood (the layer next to the bark) is generally higher in MC than heartwood (inner wood which has died). Sapwood distributes water and nutrition through a tree. The heartwood, or inner wood, becomes infiltrated with gums, resins, and other materials.

This makes it more resistant to moisture flow and thus, the heartwood usually requires longer drying times than sapwood. Sapwood and heartwood will affect the drying curves for each wood species.

A wood’s MC is also a dynamic exchange between the wood itself and the surrounding air. When the relative humidity (RH) in the air rises, wood absorbs moisture from the air; when the RH falls, wood releases moisture into the air. This occurs naturally, and it occurs throughout a wood product’s lifespan even after it has been harvested and kiln-dried for human use. Wood producers, builders, and consumers need not fret over such an organic, natural process, but a thorough knowledge of it will guarantee success with wood in all sorts of product applications.

The key to wood strength and performance over time is to dry the wood appropriately to its optimum MC depending upon the end product’s service conditions and the end product’s installation destination.

There’s Kiln-Dried Wood

Kiln Dried Wood

Wood in “green” condition must be kiln-dried in order to be used as construction grade lumber for building purposes, as an example. Lumber production is a complex process in which green timber is sawn, dried and processed. The natural air-drying of lumber can be a long process, so oftentimes lumber will be kiln-dried to speed the process along. Kiln-drying is basically a process of placing sawn lumber into kilns where heated air is circulated and the temperature and RH of the kiln is controlled for the purpose of reaching the wood’s equilibrium moisture content (EMC): a balance between the MC of the wood, and the RH of its surrounding environment, depending upon the end wood products application specifications. Once the EMC is achieved, a wood’s MC can vary with slight changes in the RH of the surrounding environment without jeopardizing the strength and structural integrity of the end wood product.

Lumber producers deploy expansive and expensive wood MC control systems at all phases of wood production. Kilns are an integral part of the wood’s MC measurement and management process, as the kiln-drying procedure is where the green lumber is dried to its optimum EMC.

There’s a Moisture Meter to Measure It

A wood moisture meter is crucial in establishing and maintaining healthy wood MC levels at each stage of lumber production. A wood moisture meter is a tool which measures the wood’s MC. As green wood circulates for processing in a mill, in-kiln and in-line MC systems measure and document the wood’s MC and track the efficiency of the kiln-drying process. Professionals carefully monitor and control the process to optimize the harvest. Kiln operators and quality control personnel deploy hand-held wood moisture meter products to conduct as many spot-checks as needed to verify the mill’s kiln-drying efficiency.

Ecology is merging with forestry in the modern era to make MC measurement and control an ongoing matter of wood maintenance. Wagner Meters, a family-run industry leader in MC measurement technology, has developed several wood moisture meter products to assist industry specialists, retailers, wood flooring installers and owners and hobbyists in protecting their investments.

As the world awakens to its own nature, wood moisture meter technology has advanced greatly. Wagner Meters features pocket size digital and analog styles of its wood moisture meter products. Now there’s a cost-effective, reliable wood moisture meter to suit any wood measurement application goal, from the home to the lumber producing mills.

To learn more call: 800-634-9961.

Larry Loffer is a senior technician at Wagner Meters, where he has over 30 years of experience in wood moisture measurement. With a degree in Computer Systems, Larry is involved in both hardware and software development of wood moisture measurement solutions.

21 Comments

  1. Kenny says:

    How would I kiln dry driftwood

    • Larry Loffer says:

      Hi Kenny,

      Fresh sawn wood drying in a kiln is a much different animal than driftwood that has been soaking in salt water. Kiln schedules will vary depending on the species and the amount of time in the water. There may be different species from piece to piece. Moisture detection equipment will be influenced by the salt content.

      You may want to post your question on http://www.kilndrying.org; it has experts from various fields that can provide more detail.

  2. Yuri Gartenberg says:

    Hi, I wanted to get some studs but they are klin dried, so I’m a bit worried
    the process only uses heat? no chemicals whatsoever? I wanted them to build a part of my lizard terrarium, so no chemicals

    • Larry Loffer says:

      Yuri,

      Kiln drying itself in the United States does not use chemicals. I don’t know about other countries. Some lumber mills “Pressure Treat” wood after kiln drying to withstand harsher environments better. It would be safer to use “Green” or non-kiln dried wood with animals.

  3. JB says:

    Could you use fresh sawn “green” oak wood just weeks after its cut to build a piece of furniture, such as a table?

    • Larry Loffer says:

      JB,

      Typical moisture contents for making hardwood furniture is 6% to 9%. Your oak can be worked into furniture if it had enough time to dry to that moisture content.

      Thank you,

      Larry

  4. Dennis Merritt says:

    Processing firewood from all species of wood. How can we stop the development of mold after we shrink-wrap the firewood and prepare to ship?

    • Larry Loffer says:

      Dennis,

      Obviously, completely air drying, or “Seasoning” the wood before it is wrapped will prevent mold…. And reduce the shipping weight.

      If drying before wrapping is not possible then there are spray products on the market that are “Mold Inhibitors” that you can spray the wood with before wrapping.

      Another possibility is to not wrap the wood airtight. Allowing it to “breath” will reduce mold. Perhaps use a strong perforated wrap?

      Hope this helps.

  5. Shankarlal says:

    Hi,
    I am exporting teak woods from africa to india for my own sawmill ,
    Now indian goverment asking methyl promide certificate or KILN dried , but in African country’s banned methyl promide since 2002. Or the alternative solution is KLIN drier . This kind of KILN drier where can I get this machine .and what the cost ?

  6. Denee M Buchko says:

    Hey there
    I’m wondering, if when Pine is kiln dried, all of the oils are removed from it? Is there a 100% effective way that pine can be kiln-dried? It is important for my use, as I have animals in which the natural oils in pine are toxic to. I have been told that kiln dried renders it safe, but can’t find any real information about if this is true.

  7. Denee M Buchko says:

    Thank you so much!!!!!

  8. Linda says:

    I live in New Orleans area. A contractor installed tongue and groove kiln dried wood on my front and back porches. He then used an oil base primer and 2 coats of Sherwin Williams industrial enamel. Within 6 weeks the paint started peeling and sometimes the primer came up, too. It has even peeled in areas outside of the railings where only rain and sunshine touch it. The paint seems to shrink wrap the wood after a few weeks then start peeling.

    Contractor just wanted to touch up paint but every day there is a new little section peeling. I went to Sherwin Williams who said they do not recommend primer on wood floors for their industrial enamel. They say paint and primer should be removed and then repaint the porch. They have offered to supply more of the same paint. Contractor doesn’t want to sand and is saying that kiln dried wood must be primed according to a warranty.

    I’m being told that would must have primer and the paint must not have the primer. At this point I think I’d rather have the floors sanded and put water proofing stain. Any suggestions would be greatly appreciated. Thank you!

    • Tony Morgan says:

      Listen to the paint experts. There may be a problem with the enamel bonding to the primer in this case. Staining the porch might also be a good choice. But either way, it looks as though the job will have to be re-started from scratch, with the surface needing to be sanded down.

  9. Jack Patrick says:

    I’m looking into building my home through the process of milling my own lumber. What is the best way to allow wood to dry after milling in order og get building. What’s the timeline on allowing wood to dry and what’s the easiest method in doing so?

  10. Steve St.Clair says:

    I’ve noticed a yellow pine sawmill nearby is kiln drying lumber for only a few hours. The lumber is continually fed through the kiln with lumber sticking out both ends and the doors never closed. They don’t put slats between the boards to provide air circulation either. Their bundles are about 25 ft by 25 ft. I don’t see how the lumber could be properly dried in this manner. Also, after kilning the lumber is left outside in the rain, Example: A tropical storm recently passed through. We got a lot of rain. Some railroad cars loaded with lumber got very wet. Just before shipping, the white plastic covers were placed over the lumber. Does this make sense? Are they properly kilning the lumber?

    • Larry Loffer says:

      Hi Steve,

      Sounds like your neighbor has what’s called a “Continuous Kiln”. These are fairly new and the science behind them supports more even drying along with energy savings.
      They typically will insert “stickers” between each layer for optimal air circulation.
      Perhaps their goal for this batch was not to dry the lumber. Sometimes mills will heat the wood enough just to kill insects.
      Or, maybe this batch was sold as green (Not kiln dried).

      I share your concern if they sell this as kiln dried lumber.

  11. Chris Houghton says:

    Hello Larry,
    I have to fix a floor joist that in the basement supporting the first floor. The joist is 13 feet supported at both ends. The rot extends about 4 feet from one end. Because I cannot get a 2x8x13 board into my basement and put it in place, I will be trying a 12 foot length and possibly a 10 foot length and sistering it to the existing joist, which is in good shape other than the last 4 feet, and supporting just one end of the new joist, shimming as necessary.

    The existing joist is 2×8 Fir and is slightly larger than the modern green boards. My question to you is should I use a green board or either a kiln-dried or air-dried board to avoid crowning and shrinkage as the new board dries? My local lumber yard tells me that dried lumber has to be special ordered and could take up to 3 weeks to obtain.

    Thanks for any help you can extend.

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