Woodsense: Spotlight on Koa

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Koa

Technical consultant: Larry Osborn

If you’re lucky enough to live on one of the Hawaiian islands, then you no doubt are intimately familiar with koa – a wood of rich browns and reds which tends to display interlocking grain and, in some cases, eye-popping figure.

Unfortunately, for most of us, koa wood can be hard to come by (and it’s pricey!). The koa tree (Acacia koa) grows natively only in Hawaii and while previously prevalent, it is now increasingly sparse due to logging and the clearing of land for pastures. The tree itself can reach around 80’, taller if growing in volcanic ash. Koa is a member of the pea family and as such produces pod-like legume fruits.

Most koa for sale ranges from stock having a golden brown color to mahogany-like reddish browns to darker walnut-like browns. Color can vary widely within a growth ring, thus color banding similar to that in zebrawood can sometimes result. Curly, wavy, and interlocked grain are also common. Koa has no natural decay resistance and is a favorite of termites, hence exterior buildings do not frequently contain koa.

History in woodworking

Before fiberglass entered the scene, Native Hawaiians utilized koa for body boards and alaia (finless or skegless) surfboards, as well as dugout outrigger canoes. Due to deforestation, koa trees of the necessary size for larger projects are harder to come by. Today, many woodworkers in Hawaii turn to koa for furniture, decorative boxes, turnings, and carvings, with many of these items sold to tourists. In addition, a substantial industry has cropped up around the use of koa for guitar veneer and for the guitar body itself. It is routinely seen in ukuleles as well. The reason: koa is considered a ‘tone’ wood, making it suitable for the building of select musical instruments.

Where the wood comes From

Koa only grows on the islands of Maui, Hawaii, Oahu, Kauai, Lānai, and Molokai. The ideal growing range is from around 2,000 to 6,000 feet above sea level where the trees take root in a rich, dark volcanic soil. Harvesting koa is highly regulated and much of what is used now comes from reclaimed wood. There is a koa plantation north of Hilo, Hawaii, where patient investors can buy young trees, have them planted, and then sell the wood years down the road once the trees mature.

Koa

What you’ll pay

Koa is increasingly expensive. Because of its limited distribution, you will just as likely find yourself purchasing specific pieces in addition to buying koa by the board foot. It’s comes down to availability at the time of purchase. Some sample online prices include the following: a 2 × 13 × 71" board of curly koa, $900; a curly koa turning blank of 5 × 51⁄2 × 11", $90; and, by contrast, an unfigured 2 × 41⁄2 × 38" board, $75. You can generally find better deals on eBay, but be warned – you may find that even though the wood looks like koa in the picture, it may turn out to be something entirely different. Some suppliers in the islands dry, sell, and ship 4/4 boards that measure up to 8" wide x 8' long. One such supplier sells plain-sawn 4/4 stock for $19.95/board foot and full curly koa for $44.95/board foot. Another prices curly koa veneer at $80 for a 61⁄4 × 81" piece.

How to select the best stock

Koa is available in a variety of colors as mentioned earlier, as well as grain patterns. These typically include plain-sawn, crotch, semi-curly, full-curly, and everything in between. Some dealers will email photos of pieces they have on hand for your approval. For projects, be sure to go with a consistent color and figure. Ask about the drying and sealing. You don’t want your shipment of koa to have checked ends when it arrives due to mainland climate differences. Too, ask if the wood came from the same island and elevation. That can make a slight difference in appearance. The best case is when the pieces in your koa order originate from the same tree.

Working koa in the shop

Because of the high prevalence of interlocked grain and figure in koa, machining requires care. End grain can chip and tear out when crosscutting and routing, so slow feed rates are crucial, as well as the use of sacrificial backers. Figured koa can tear out during planing. Here, feed the stock at an angle and take only very fine cuts. A drum sander may be needed for a gouge-free surface. By contrast, standard plain-sawn koa machines easily much like walnut, producing a smooth finish when jointed or planed. Koa has a relatively high density, so when turning, employ sharp tools and a steady hand. As with planing, end grain tear-out is common on the lathe, especially when working figured koa.

Koa can eat through sandpaper, but finishes to a high luster and is worth the sanding effort. The wood does not have an odor, but like many tropical woods, koa wood dust can be a nasal irritant and a mask should always be worn when working it. Extractive content is low in koa, making gluing and staining a breeze. Oil-based stains and finishes highlight the wood’s beauty, as do water-based topcoats. Because koa is only minimally an open-pore wood, filling is not needed.

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