Kiln Dry Lumber at Home

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!

Comments

[kevinmgeaney]

Very good explanation and reasoning thank you for all the effort. Kevin

[PeterH59]

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 .

[LukeArts]

I wonder if you still think the same after 7 years =)) Timber prices have skyrocketed past Mars by now, so the weight of the effort and electricity is minimal compared to the value of the wood itself. If it's a tree from your own garden, it's definitely worth it IF it's for a project that you would do anyway, with or without your own tree.

[ringesen1]

If I air-dry pine (Southern yellow pine) for 6 weeks with end coating and Borax and high strength termiticide and then 6 weeks with electric fan, will I get twisting in vertical beams sawn to 12" by 12" and 20 feet long? Could I use sooner than 12 weeks and put beam under light compression (vertical members) load? Tak

[LukeArts]

in case it's still relevant: oversize your rough pieces to account for twisting and warping, then when they are dry, mill them to size. Such thick long beams will definitely have some deformation while drying. I would overdimension them by 10-20%. You'll need to do that too to account for shrinkage, which will be relevant for those dimensions.
If you want to make such large beams lighter without losing strength: dry them vertically and only seal them at the top. Make sure the resin (tree sap) can run off at the bottom. The resin contributes a lot to the weight, but virtually nothing to the strength. (unless maybe you intend to use them as wall carrier beams on the ground, where the resin may have some dampening function for vibrations from wind, equipment or vehicles)

[ErinM181]

Hi,
Would you mind giving me a little more of a "recipe" I suppose to your drying techniques? Im very new to this hobby and I want to make a table out of fresh cut hardwood. I also want it to be an outdoor table. Thanks for your time anyway.

[rread396]

The drawback of this method is the power consumption. Four months with a fan (say 35W) and dehumidifier (about 240W) is about 800 kWh, which would be a substantial addition to a power bill.
Out of interest what was the ambient temperature? At low temperatures the rate of drying would be slow, while these dehumidifiers are usually designed to cut out at 32 C.

[LukeArts]

Or it could be a great way to increase your consumption of your solar production... (in Europe, domestic power production is metered, the injection capped and the sustainable power certificates are based on production, not injection. So to allow for more production, you need more consumption... Yea, it's a redundant system, but you'd earn money by wasting electricity this way)
However, I had the exact same reaction as yours in my mind. Not for the bill, per se, but just for the ecological aspect.

[curlygirlthree]

what percent of moisture did you start with?

[Tgomez36]

I’m not sure how to ask this but I hope it make sense. What would be the best way to slice the log into slabs to prevent splitting and twisting? Is there a rule of thumb to follow? I’m getting ready to process a winged elm. Thanks in advance.

[ShawnaC14]

What type of wood is this?

[Bmmyers8]

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.

[TR25]

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.

[TR25]

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.

[Mike Dalton]

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.

[poock224]

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

[SemeleA]

High frequency vacuum wood dryer www.hfwoodmachine.com,email [e-mail]

[akyle5]

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

[Duran_riel]

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.

[jJohny]

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.