Kiln Dry Lumber at Home

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Introduction: Kiln Dry Lumber at Home

About: I enjoy sharing what a life in the woodworking trade has taught me.

Kiln drying your own wood at home can be a great way to sustainably harvest the materials around you, and dry it fast enough to build furniture with. If furniture is made with wood that is too wet, it will continue to dry and crack, possibly ruining the piece. This instructable takes you through the process of raw wood in the spring, to dry lumber in the fall. You can do this with any kind of wood.

Step 1: Mill Up Your Wood

Finding rough timber and logs to mill is a lot easier than you may think. There's always someone around that's trying to get rid of a fallen tree or wants to take down a dead tree. Calling around to local tree trimmers and arborists can lead to some great opportunities. These people make a living with trees, and if you can offer them a fair price for a log, they'll often choose to sell it because it saves them the work of disposal, or processing it into firewood. Put an add in the paper, call your local city or municipality and ask about who deals with downed trees. The list goes on and on, but you can definitely find something. The term "windfall" comes from just that, wind storms can mean lots of wood.

Once you've gotten the wood, local sawyers are plentiful in most areas, and many will bring their portable sawmill to you for a very reasonable rate. I pay $100 an hour here, and a good sawyer can do a lot in an hour. Worth their weight in gold, these hardworking folks are a woodworkers dream come true, and they often have a stock of amazing, local woods for sale.

You can also choose to mill it yourself with a chainsaw, which I partially do sometimes depending on the log. If you choose to do this, read up, and follow all the safety precautions of those tools. And like anything in woodworking, protect your eyes, ears and lungs.

Step 2: Wood & Moisture

If you don't seal the end grain of your logs and timbers, they will crack and split as moisture is perspired. The end grain needs to be sealed up with a material that will close up the open pores of the wood. I often mix 50/50 wood glue and water then saturate the ends several times. You can also use paint or wax. These logs all started off at a pretty normal 32 percent moisture content.

Step 3: Air Drying

Start off by air drying your wood for a few months to shed the first bit of water naturally, maybe a loss of eight to ten percent. Stack the wood up with plenty of spacers, or stickers, to allow for good airflow, and I like to put a piece of plastic on the ground under the wood to keep the humidity from the ground from effecting the lumber. I bind the wood with tie downs to minimize cracking and twisting, and I build a temporary plastic roof to keep off the rain. Place it in a location with good prevailing winds, it makes a big difference.

Step 4: Build the Kiln

After a few months, bring the wood indoors and finish the drying. To build the kiln lay poly (clear plastic roll) on the ground and then build a frame with 2x4 studs on top of it for the lumber to rest on. Leave enough space to have a standard household dehumidifier at one end, and a small fan at the other.

The fan circulates the air to even out the drying. I designed mine to pull air from below, then blow the air down a plastic tube to the other end. This way I know there's no stagnant air or dampness trapped in the kiln. This one is 20 feet, or 6 meters, long. The dehumidifier is also trapped inside the kiln and is set to maximum. This model has a hose that runs out of the kiln and fills a bucket.

The kiln is built around the stacked and bound lumber over a light wooden frame that carries the plastic. All seams need to be sealed with vapour barrier tape to hold the moisture in. I cut a few small access holes to control the dehumidifier and to test the woods moisture content in various places. Tape up these holes after you use them. The wood remained in the kiln for about 4 months and reached an average of 8 percent. This is mostly 2" thick arbutus, also called madrone.

Step 5: Using the Wood

Bring the wood into your workshop and allow it to acclimate for a few weeks, then start processing it. You can see here that the 1" thick material is below 7 percent, excellent for making furniture.

Step 6: Making Furniture

Using this unique wood often presents the opportunity to really showcase a unique piece of wood that you can be proud of harvesting in a sustainable manner.

Thanks for taking the time to read through this instructable, now get out there and save some logs!

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    We have a be nice policy.
    Please be positive and constructive.

    Tips

    not all sawyers know what they are doing. I asked for some quarter sawn oak and he started cutting parallel with the grain instead of perpendicular. He did not understand. I tried to correct him but the best part of the wood was ruined for quarter sawn. So have the confidence to double check and confirm that you are getting what you wanted. That means draw a picture on the log if that is what it takes.

    3 Questions

    What type of wood is this?

    Just copied the kiln...more or less. I am wondering if you let the fan and dehumidifier run 24/7 or did intervals? And if you do intervals what are they? Thanks.

    I read that one of the important parts of kiln dried lumber is that it is heated to kill bugs. Should be heat the wood using a solar wall or something like that or would it dry out the wood to fast. I need to process red oak.

    58 Comments

    Great idea for a home workshop! No permanent space is needed and, with the right exposure, solar heating could be added via a section of dark stove pipe the fan blows through.

    We made a large kiln for a Boy Scout camp using the body from an old dairy delivery truck. We air dry for about one month, then rack the wood in the kiln and use a dehumidifier and small fan. With the insulation, we can use the kiln in the winter (in Ohio) as the returned heat from the de-humidifier and the fan motor are sufficient, or we can add a small heater. The kiln is nearly air-tight and the de-humidifier drains through the floor. An alternative to a de-humidifier is a simple recycled window air conditioner where the cooled (dried) air is directed back through the compression coils and then out to the racked wood instead of exhausting the heated air outdoors. This arrangement should have a higher capacity than most de-humidifiers.

    Our kiln can dry enough wood to supply our planner/shaper with all the lumber to frame and side a 20' x 20' building.

    1 reply

    i know this was a while ago but can you give me some more info on using an old a/c unit i have wondered if i could do this

    High frequency vacuum wood dryer www.hfwoodmachine.com,email haibo8@vhaibo.com

    Doesn't the fan just push in humid air and negate the dehumidifier?

    2 replies

    the fan is inside the plastic "room"( if you look close you can see the base of it in the pic) basically it just circulates the air inside the kiln, the plastic tube directs the damp air towards the dehumidifier without blowing over the lumber again. Be warned home dehumidifier are not designed for wood drying. The coils will slowly deteriorate from the acid in the wood. Coils in wood kilns are coated for protection. Coated with what?....I have yet to find out.

    Just a thought but the coils might be helped by lightly spraying them with a rattle can of outside grade clearcoat. On the other hand you don't need to collect that acidic stuff. More humid air tends to rise so you could just blow the heated and dried air in from the bottom of the kiln and then top vent the acidic vapor straight out the nearest window.

    Mark Twain (Samuel Clemens) once said, 'It took me 7 days to get over the worst cold I ever had, but with proper medicine and rest, I was able to get over the next one in only 1 week'. The humor being, it took about the same time either way. In the U.S. Southeast (summer temps around 100F in the day, always near saturation at 100-percent relative humidity), a couple of my friends and I built a simple three-walled 'pavilion' structure to put poplar 1-inch planks in to 'air-dry'. We cut, run 1/8-inch strippers between layers, thousands of board feet, and in about 5-6 months, we could take 35-40 percent green poplar down to 10-12 percent wood water by simply running a barn fan (42-inch diameter 1 hp motor) at the end of the pavilion, blowing through the planks. I'm still not sure of the exact mechanics of how this worked due to the high relative humidity, but with no monetary investment beyond building the pavilion and the electricity to run the fan (pennies a day per thousand board-ft), I can't look a 'gift-kiln' in the mouth.

    very impressive. The only bummer is the cost of electricity to run the dehumidifier and all the Labor involved makes me wonder about the economics .

    You can build a re-saw for cheap to cut your logs into boards or planks. All you do is mount 2 tires on a frame. One stationary with a motor and the other needs to have an adjustment from side to side for the tracking. The only part that might cost is a 4 inch band saw blade. The whole set up works just like a belt sander.

    Thanks for sharing this! I got a bunch of logs on my lawn that I got from my neighboor...now that I've got the right tip to properly dry it, I may finish up some of my furniture projects. ;D

    Thanks for sharing this! I got a bunch of logs on my lawn that I got from my neighboor...now that I've got the right tip to properly dry it, I may finish up some of my furniture projects. ;D

    Thanks for sharing this! I got a bunch of logs on my lawn that I got from my neighboor...now that I've got the right tip to properly dry it, I may finish up some of my furniture projects. ;D

    Thanks for sharing this! I got a bunch of logs on my lawn that I got from my neighboor...now that I've got the right tip to properly dry it, I may finish up some of my furniture projects. ;D

    Thanks for sharing this! I got a bunch of logs on my lawn that I got from my neighboor...now that I've got the right tip to properly dry it, I may finish up some of my furniture projects. ;D

    Awesome ible! Great writing too, I was really drawn in and wanted to learn more about how you collect and use wood.

    I love how you took it from raw lumber. Very cool!

    Great instbl! I have lots of interesting hardwood logs here in Zambia. But always with high humidity!

    If it will not be put through a disinfection heat cycle, I would treat all 4 sides of any freshly cut lumber with a Timbor solution when it's fresh off the saw as you stack it for the first air drying. This will very cheaply and easily prevent wood boring/eating insects forever and when absorbed by the wood is not toxic to people or pets. You can make a diy version (US Navy spec.) by mixing 6 parts Borax (20 Mule Team laundry booster) and 4 parts Boric Acid powder (Amazon). 1.5 lb of this mix dissolved in 1 gallon of water and then sprayed on with a garden sprayer will treat 220 sq. ft of lumber. Wear waterproof gloves and a mask when mixing and spraying.

    Wood above 8% moisture level will support Powder Post Beetles. The problem is the time (weeks/months) it takes to get to this level.

    1 reply

    awesome, I just built a rotary axis for my CNC router and picked up a couple of live oak logs to attempt some 3d caring with. I'll give the borax/boric acid treatment a try with the logs.

    IMG_0917.JPG

    Saw this kiln in Mexico a couple of months ago. Green dimensional lumber is stacked up around an open fire.

    kiln.JPG