We often get inquiries to supply koa and other Hawaiian wood lumber. Most times the customer wants to use it right away, so of course will need "dry lumber to work with. But what if you don't need it right away and all you can find is "green" lumber? Let's discuss that and perhaps you will find some of these points a good review and help you discover a new world of woodworking.

Over the decades, and if I include my father's operations from the early 70's, the Winkler have milled and dried MILLIONS of Board Feet of Hawaiian Koa. Yes, that's right, 7 figures, and if we include non-Koa species I think that number might even be in the 8 digits! Wow, even I'm impressed thinking about it. While I'm not trying to "toot our own horn" I share that info so you understand we have gone through so many different problems and issues to come up with fairly consistent methods to produce quality dried Hawaiian-grown woods, hard or soft.

I say "fairly consistent" because even after all that experience, we have still had problems happen, despite doing everything as we should. I can vividly remember one experience of "sticker stain" on some of the curliest, most beautiful Koa, we cut that year. We were devastated! What is sticker stain? What is a sticker? So before we talk about sticker stains, let's discuss some of the science of wood and terminology you'll find when talking about drying all species of lumber.

Disclaimer - I am NOT a scientist nor will I get too technical here, so scientists out there, please forgive my layman's explanation here. This is meant to be a general overview of how to dry wood and why it is necessary before using it to build, and I'm not talking construction, but furniture, instruments, etc. 

Trees, like humans and most of living things, are made up of mostly water. Depending on the specie of tree or the particular season, it could be as much as two-thirds water! While that is great for the tree to continue to keep living, it isn't good to have that much water in a board that will be used to make a piece of furniture. Why?

The board cut from a tree that is still "green", which I will propose to be over 15% moisture content, will need to be dried further to become a "dry" piece of wood. BTW, there is no real definition of green or dry wood that you can lookup because it really depends on the specie and where one is building.

Moisture Content "MC" is the percentage of water in the wood. We use moisture meters to get an exact percentage. I use a very expensive (~$800) Lignomat pinless meter that uses radio waves bouncing around in the wood to give me the wood's MC. As long as I tell the machine the specific gravity, also sometimes referred to as the hardness of the wood, it can give me a highly accurate measurement of the moisture content. Oh, Koa is usually set to around 56, but even Koa ranges in density, but using that will give us a close enough reading. The moisture meter makers will provide the table of almost all species.

A piece of wood could be as low as 4% MC or when just off the mill 60%. While most of the industry will consider a 12% MC to be dry enough to build, it will ultimately depend on your own environment and relative humidity where the piece being built will ultimately reside. Generally using a kiln we dry wood down to around 6~8%, but once it leaves the kiln it will change and absorb more water from it's surroundings or even sweat if it is in a very dry environment.

Will you build a table in Hilo in an open garage and then put it in an office that will have the AC on for most of the day? If so, you really have to pay attention to the MC of the lumber you are building. Why did I choose Hilo? Well, Hilo is on the East side of the Big Island of Hawaii and you can almost never get any lumber below 16% if you don't purposely do things to get it below that level.  Since my father's primary shop and mill was in Hilo, we had to use dehumidifying kilns to "suck out" the water to bring the lumber below 10%.     After that we put it in our warehouse and it would often hover around 10~14% depending on the board. This was good enough for our customers and definitely be considered "dry" lumber. Had we not used a kiln, we probably would never get the lumber below 16% unless we put in a dry environment and kept fans on them.

Kailua-Kona on the West side of the Big Island can put a stickered rack of lumber in a warehouse near the rafters and have 1" Koa lumber dry to 6~8% within 4 - 6 months without any equipment, kiln, fans, etc. Huge difference from the East side of the Island. This can probably be said of almost any Hawaiian Island where the East side is so wet and rainy - Hana vs Lahaina and Kanehoe vs Ewa Beach for example.

Drying Wood - The goal is the take the water out of the wood to the correct moisture content. This can be done naturally without the use of any equipment by stickering the lumber and letting the wood sit over time in a dry area. In a reasonably humid environment, like Hilo, kept under cover and stickered, it takes around a year per 1" of thickness.

I won't go into all the science how how the water leaves the wood or why, but basically wet wood will release moisture in a dry environment and take-in moisture when it's wetter outside than the wood. Have a look at a solid wood flooring - it will actually swell and shrink in different seasons or environments.  It's the same reason every winter when I put on the heater in my office, the door to my storage room won't open because it changed due to it's drying more on my office side from the heat and causes it to bow slightly to get a little stuck. So, I have to walk around to the other side and open it so it gets back into it's track properly. This only ever happens when I have the heater on in my office.

This is one of the main reasons a builder must ensure his wood is dry enough before working with it. If the wood is still in the water-releasing phase of it's conditioning, it will continue to release water and shrink even after made into a product. Ever had a a piece of furniture or instrument start to split apart at the seam or joint where two pieces of wood were glued together? That is the result of the piece of wood not being dry enough for the environment for which it was placed. If you know your piece of furniture is going to be an a very arid environment, ie Arizona, or in an air-conditioned office, you'll need to be extra careful your wood is a very low moisture content at least 8% or so. This is not a strict rule for every specie. I'm referring mostly to the Hawaiian Koa wood and other medium level hardwoods. Even some medium level are prone to cracking and causing problems you won't find using Koa (or walnut since they are both very similar in density and workability).

Stickers - these are the boards, or half-cut PVC pipes, placed at regular intervals between each layer of green koa in order to allow air to pass through the stack to touch both the bottom and top of each piece of lumber. Using the correct specie of wood for stickers is very important, otherwise the wood you are drying might react with the wood used as a sticker to produce the "sticker stain" referred to earlier. This is an actual chemical reaction causing discoloration that sometimes will penetrate millimeters into the wood. What specie should you use? For koa and all our other Hawaiian woods, we used a mixed of South American hardwoods - we bought actual "stickers" which were mostly ipe and other hardwoods like that. In the 70's and 80's when koa wasn't $100 per BF all our stickers were either koa or Ohia. Ohia also makes great stickers.

The sticker stain happened to us on one particular log of koa that had never happened before using the same stickers we always used for years! I called everyone I knew to get more info and in the end we concluded it was just a strange log with minerals in it that weren't in other logs. In the end we only "lost" around 5~10% of the batch because we were able to sand enough of the wood away to go beyond the stain. But we were almost crying when we first pulled out the material and saw a "shadow" or discoloration on our koa guitar wood every 3" apart! While the stain would not actually physically affect the performance of the wood in a finished product it would have been a bit unsightly and aesthetically unpleasing.

Ideal sticker size and placement - usually no more than an 1" wide and 1/2" to 3/4" high. A rectangle is preferred to a square so that you always use the same side when putting them on the board. Stickers can warp or bow, so when they do, you'll want to be sure you are putting a bad sticker in the batch. Intervals should be no more than 4" ~ 5" for 1" and thicker wood. If you are stickering thinner boards, you may need to decrease the interval. The wood may bow if the stickers are not placed close enough to each other. The stickers should also be aligned from top to bottom directly above and below each other. This prevents wood bowing.

DIY Drying - don't have the few thousand for a proper dehumidification kiln? No problem... a little space, some cheap box fans, a bunch of stickers and if you really want to provide some heat, an oil heater like a $100 Rinnai. If you want to go the distance, you can also include a household dehumidifier but you'll need a fairly well-enclosed area if you add that.

The science of it is simple - air flow and heat are the two main ingredients to pull water out of the wood assuming it's not sitting outside in the elements. Sticker the pieces as detailed above. Place as many fans as you can so the entire pile has wind going through the boards. Oh, be sure you are not blowing the wind into the sticker, meaning if you look through your pile, you should be able to see to the other side. If you are looking at the edge of a sticker, don't blow it that directly.

How wide should the pile be? It depends on the area you have to use and how big your pile is, and how long your stickers are. Our stickers are either 2' or 4' depending on how much wood we need to sticker. The air will flow the length of your sticker so if you make them too long, the air will have a difficult time to flow from one side to the other, unless you are using some massively powerful fans!  But for the simple, cheap box fans, no more than 4' is recommended.

Start with your longest boards on the bottom. This allows you to not have any boards hanging over boards below them which means they won't have any sticker support under them causing them to bow up or down. Boards should always have enough stickers to go from one end to the other.

A sticker at the VERY END will help prevent "end checking" which are the cracks that occur because the wood is shrinking at different rates. End checking is the most common problem you will see when trying to dry wood. Some will bound to happen, but the more care you take to put the stickers as close to the end of the boards as possible, with weight above them, it helps prevent it. The weight above keeps the boards "tight" so the water takes more time to leave the wood, which allows the rate of drying to slow down and prevent the cracking.

I mentioned the oil heater because it produces a low intense, steady heat which you can control and prevent a fire and keep the heat from being concentrated in one area. It's more of an ambient heat rather than a pinpoint. We put heaters in front of the fans to push the warm heat through the lumber.   
You can even build a box or plywood enclosed area to put the heaters and fans. Add a household dehumidifier and you will have a true DIY dehumidification kiln for a few hundred bucks!

Why go through all that trouble? Well, for one thing, you can never know for sure how dry the wood is you are buying from any particular place. With us, we gladly put the moisture meter on the wood to show what it is at. Not sure about other places. If you plan to do any kind of woodworking long-term or build things you expect to last, good idea to invest in a moisture meter. You may find that "dry" wood you have been buying is actually too wet to build with.

More wood at a cheaper price - drying wood properly takes time and effort which means their are real dollar costs to providing dry wood. If you set yourself in a position to dry your own wood, you will essentially "pay yourself" to dry it.   Some mills also ONLY sell green lumber. Some will offer it if you ask which will most likely be at a discounted price. You may also get a better choice of lumber - imagine being the first one at the mill able to choose the logs you want. And in some cases, you may get some curly or figured lumber you didn't have to pay the price for the higher grade, especially if you are buying logs. We don't sell koa logs, so please don't ask...

In the past, when we had a larger mill operation, we had to make sure we always had enough money to pay all the bills. This meant selling green lumber right off the mill and getting it sold as soon as possible. It wasn't feasible to wait or pay the extra fees to dry it. And then there is the issue of storage. You need a warehouse to store all that dry lumber. When you are milling 5,000 ~ 20,000 BF of various species of lumber per month, that will very quickly take up a LOT of space.

Some final thoughts - most all our Hawaiian species offered are salvage or re-purposed. Some of the koa logs we find have been on the ground for many years and have already mostly dried so when we mill them up they are already in the teens as opposed to the usual 40~50% MC.

I would like to also take this moment to dispel the rumor that I continually hear, "I heard koa is a protected specie and it's illegal to cut down." I've also heard koa is just illegal to trade. Well, not true for either of those claims. In Hawaii, you are allowed to cut any tree down on property you own unless it is conservation zoned, which is generally unlikely for most privately owned property (that's an entirely different topic). Unlike Washington state, and perhaps others, there are no laws or ordinances preventing you from chopping trees down on your own property.

In Hawaii, as long as you don't alter the original topography, you can cut down every tree, piece of grass, or whatever you want. This may seem odd and not very "nature loving",  but you also must remember, many trees and plants on people's properties in Hawaii are actually introduced species. That huge mango tree that it about to fall over and crush the neighbor's house, was not in Hawaii naturally. That topic will also be part of another blog - "Hawaiian Forests - Then, Now, and 50 years from now"

If you have anything to add, comments or questions, feel free.

Mahalo and happy drying !
January 13, 2023 — Jorma Winkler

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