Yes, koa is a terrifying wood to build with, so I always start with quartersawn sets. It helps to keep the sides thin for easier bending but caution dictates installing 10-12 vertical braces to reinforce the sides and prevents splits. Over time, I’ve come to depend on a contact thermometer when bending koa and I never heat past 265 degrees; better support the sides well when bending and go very slowly; don’t soak koa, especially if curly!

It’s always in my mind that all figured wood is defective to some degree and the more highly figured it is the more defective it is—especially curly woods. The fact that it’s so pretty drives builders to use it, but the best instrument woods are quartersawn and straight grained. It’s no coincidence that so many old guitars (esp. Martins) were made of straight-grain Brazilian back when luthiers could just as easily have obtained highly-figured stuff.

It’s the job of builders to educate customers about the advantages of using less-figured woods. But first, we have to convince ourselves because we all love to build gorgeous guitars and figured woods are hard to beat for eye candy.

While koa is enjoying a resurgence among both builders and players these days, perhaps some consideration should be given to past experience with the material. Generally the old chaps at Martin who had been there when a lot of the species was being used there tended to dislike it as a building material.

While it can be stunning in appearance, the general opinion among those old Martin hands was that the plainer wood tended to yield the better tone and was more reliable structurally.

Koa does not have a great deal of stuctural integrity along the grain, in fact when thinned to guitar plate or rim thickness it may start to unravel like hemp rope if dampened during the bending process. In addition, the highly prized curly koa often tends to crack at the ‘curls’ when being bent.

Curl or fiddleback figure is caused by end grain coming to the surface of the wood where you wouldn’t normally expect it. With more robust materials like maple, the wood is strong enough that this repeated pattern of end grain popping up in the main body of a plank doesn’t significantly weaken the plank, but with koa the effect can be disasterous.

One builder with a lot of experience with koa has been quoted saying ‘Anyone bending curly koa rims will becomem familiar with the use of cyanoacrylate adhesives’, cyanoacrylates being the Super Glue types. He’s referring to the common practice of repairing bending cracks on the curls with Super Glue as you go. Effective, but less than an ideal way to expensive instruments.

Another very well known builder whose fame largely comes from his highly figured koa ukes and classical guitars once told me privately that ‘Koa is Hawaiian for crap’. Strong opinion there, but he has a point.

The outrageous prices often carried by highly figured koa instruments are not entirely due to the premium price of the material itself. The aggravation of having to bend the stuff and the fact that you may need to bend more than two rims for any given project come into play.

While a well made curly koa instrument can be a visually spectacular piece and some have excellent tone, potential clients need to take the relative fragility of the material into consideration before plonking down a deposit.

Many may well feel that the risk is worth it, others may not.

As a builder, I strongly recommend against the use of curly koa for tops since the factors which make the best tops are virtually all missing from koa. The vast majority of koa-topped Martins from the early days that I’ve seen have had serious structural problems directly attributable to the use of that species in a function for which it is entirely unsuitable.

Just one mans’ opinion, of course, but one formed through a fair bit of experience.

All the best,
KH
Timberline Guitars and Ukes,
Canada.