Adhesion Matters - Adhesives for Exotic Woods

Episode Date: August 4, 2025

In this special episode, we do a deep dive on the global exotic hardwood industry, particularly for musical instruments.  A key theme is the critical, often understated, role of adhesives in the manufacturing of high-performance exotic wood veneers and their subsequent impact on the aesthetic and acoustic qualities of guitars and ukuleles.   We tracked down an expert who has been hugely successful with the vertical integration of this business, both upstream and downstream.  His commitment to sustainability and deep technical understanding of adhesive interactions with exotic woods make for a great subject of interest in today's podcast.

Imagine crafting a high-end guitar, you know, a real work of art. Mm-hmm. You pick it up, feel that smooth, polished wood, maybe admire the intricate grain. Yeah, the figuring can be stunning. Absolutely. And then you strum that first chord, that sound just rich and full. It's a masterpiece, right? Definitely.

But what if the very thing that makes it so beautiful, say, a rare exotic wood is also its biggest challenge? Like, it actually resists the glue meant to hold it all together. That's often the case, yeah. It sounds counterintuitive, but it happens. So today, we're not just admiring the pretty surface. We're doing a deep dive into the, well, the ingenious, often unseen science that overcomes these kinds of hidden hurdles in high-end guitar making. Well, pulling back the curtain.

Exactly. Looking at specialized materials, these meticulous processes, and really uncovering the critical science that turns these amazing raw materials into, well, sonic works of art. And to help us figure this all out, we've got some great sources lined up. Yeah, we've got insights from the big Hawaii wood show, some detailed scientific papers looking specifically at adhesives. Yeah. And also the story of this really prominent family business. They've been dedicated for, like, generations to working with these incredible exotic woods.

Okay, let's unpack that then. This journey, it seems to start with the name, Jorma Winkler. That's right. Deeply rooted in the global wood industry. He's what, fourth generation? Fourth generation leader, yeah. His family's legacy in Sawmillan goes way back, northern California, late 1800s. And then they eventually moved the operation to Hawaii in the early 1970s.

So we're talking, you know, a lifetime of expertise spaked in. Generations of wood knowledge. Exactly. And Winkler, he has this profound, almost intuitive understanding of exotic hardwoods, especially Hawaiian coa. The famous coa. The famous coa. He started out marketing Hawaiian.

lumber species worldwide pretty early on that gave him this unique insight he saw the potential but also the challenges and all that deep expertise eventually led him to found winkler woods LLC back in 2002 you might also know them as mike high wood Hawaii and his mission was pretty clear supply Hawaiian koa and other tropical hard words globally mostly for musical instruments you know guitars ukuleleys and also high-end furniture So that family history gave him the foundation, but you mentioned challenges. What really sets Winkler Woods apart? Well, a huge part of it is how they manage their whole supply chain.

That's what's called vertically integrated, meaning they oversee every single step. I mean, from actually logging and milling the coa trees on Hawaii's Big Island. Really? From the stump. From the stump. Then the really careful painstaking kiln drying of the lumber and then the super precise processing of the instrument wood sets that happens at their headquarters in Honolulu. This kind of end-to-end control is, it's pretty rare, and it ensures just unparalleled quality and consistency in their exotic woods.

You know what you're getting. Yeah, makes sense. That level of control must be key. It is. And that vertical integration, it really speaks to Winkler's whole approach. He's not just a wood guy. He's an entrepreneur, an innovator, especially with technology. Right.

I mean, he's built multimillion dollar multinational corporations. And his business skill, it got formally recognized. My Kai Wood, Hawaii was named Hawaii Small Business Administration exporter of the year back in 2014. Okay, impressive. And his influence, it goes beyond just his own company. He served on boards for key organizations like the Hawaii Forest Industry Association, the Hawaii Export Council. And importantly, for our topic, NAM, the National Association of Music Manufacturers. So he's really embedded in the industry at multiple levels.

And it sounds like it's not just about the business side or, you know, production efficiency. that long family connection to the land, does that show up in how they operate? Absolutely. There's a strong commitment to sustainability. It's one of their core values, actually. Oh, so? Well, they aim to provide, you know, the commercial benefits of the forest to the landowners, but while actively protecting the native plants, the animals, the water sources.

It's a balance. It's a balance. And it's not just talk. Back in 2003, Winkler Woods was actually chosen by the State of Hawaii, Department of Hawaiian homelands, for a major project. Oh, yeah. Yeah, to harvest, market, and reforest over 100 acres of coa forest on monaquia. Reforest, too. That's key. Crucial.

Especially when you think about how sought after these exotic woods are in Luthori, you know, the art of making stringed instruments. Sustainable sourcing is vital. Okay, let's pivot to the wood itself then. Yeah. Why are these specific exotic woods like koa so coveted? What's the big deal? Well, take Hawaiian koa. It's really prized for this unique ability.

has. It kind of blends the mid-range focus you get from mahogany. Okay. Warm. With the bright top-end sparkle, you associate more with maple. Interesting combo. It is. And what's really fascinating, maybe the magic part, is how its tone evolves, as the instrument is played over years. It changes. It opens up, it becomes richer, sweeter, more resonant.

It literally gets better with age. Huh. Like a fine wine, but for your ears. Something like that. And beyond COA, there are other amazing Hawaiian-grown exotic used in instruments and veneers, things like Mongo, Ohio, Kamani, Milo, Monkey Pod. Mungo Wood for guitars. Oh, yeah.

Each brings its own unique look, its own aesthetic and different acoustic properties. Wow. And it's not just Hawaii either. Japanese tone woods are also highly valued. You've got Kiyaki, that's Zalkova Serada, known for a rich resonant tone. Plus, it's really durable. Then there's Tochi, Japanese horse chestnut. That's prized for being lightweight and having a balanced tone.

and Kuri, Japanese chestnut, known for a bright, clear sound. So luthiers have this incredible palette to choose from. An amazing palette, yes. But you mentioned challenges earlier. You've got these incredibly beautiful woods, amazing acoustic potential. What's the catch when you actually try to build with them? The catch often comes down to structure, to actually holding them together. Many of these exotic woods contain natural oils and waxes.

Ah, okay, like teak or rosewood. Exactly. Those natural compounds, they inherently repel moisture. Yeah. Which is great for resisting rot, but... Bad for glue. Bad for conventional wood glues, yeah. It makes them incredibly resistant to bonding properly.

You can end up with really weak joints. That sounds like a fundamental problem for an instrument that needs to withstand string tension and vibration for decades. It absolutely is a huge problem. So overcoming these bonding issues, it requires really critical surface preparation. How do they do that? Typically, it involves cleaning the wood surfaces, often with something like, isopropyl alcohol. To get rid of the oil. Exactly. Disolve and remove

those natural oils and waxes. Think of it like degreasing a pan before you try to cook, right? You need a clean surface. Leak sense. After cleaning, there's usually a controlled ruffening of the surface, some light sanding or abrasion. Why ruffin it? It ensures maximum glue penetration.

And it creates what's called a keying effect. The adhesive can literally interlock with the wood fibers on a micro level. Like little anchors. Sort of. Yeah. But it's delicate. You have to avoid over sanding or using way too much clamping pressure. That's that.

Because that can actually damage the wood fibers right at the surface or squeeze out too much glue. And you end up compromising the bond you were trying to create. It's a fine balance. Okay, so the prep is crucial. Which brings us then to the unsung hero here, the glue itself, the adhesive. The star of our show in a way. It seems like the choice of adhesive is truly pivotal. It's not just about, you know, strutely.

strength or flexibility. No, not at all. It actually impacts the acoustic properties, the sound of the finished guitar. Critically, it's not just sticking wood together. It's influencing the very voice of the instrument. Okay, let's break that down. What kinds of adhesives are we talking about in Luthrie? Right.

There are several key types, and Luthiers choose carefully based on what they need. First, you've got the traditional stuff, like animal glue or hide glue. The really old school method. Centuries old. It's known for creating a very brittle, very rigid joint. And crucially, it has virtually no creep. Creep? What's creep? Creep is when the glue slowly deforms or stretches over time under constant stress, like string tension.

You definitely don't want that in a stable guitar joint. Right, you want it solid. Exactly. Hide glue's rigidity optimizes the transfer of vibrational energy. That means potentially better volume, sustain, responsiveness. Plus, a huge advantage. It's water soluble. Meaning.

Meaning repairs are much easier. you can often steam the joint apart without damaging the wood, it's reversible. Ah, that's clever. Okay, what else? Then you have the really common ones today, like PVA glues, polyvinyl acetate, think tight bond, that kind of thing. Yeah, the wider yellow wood glue

most people have used. Right. Widely use, they're water-based, non-toxic, pretty strong, but... There's always a butt. There is. Some luthiers worry about the plastic joints they form. They can be a bit more flexible than hide glue,

and they can creep over time. The concern is that this flexibility might dampen the acoustic resonance slightly compared to harder glues. So a potential trade-off between ease of use and maybe peak acoustic performance. Potentially, yes, it's debated. Now, moving on to the high-performance options,

urea formaldehyde resins, UF resins. Sounds serious. They are. Highly regarded for exceptional strength, especially good for curved laminations, like bending sides. They cure incredibly hard, like rock hard. And that hardness is good for some.

sound. Very good. That rock hard state allows vibrational energy to transfer super efficiently. Think of the string vibrating the top. That energy needs to move through the joints to the back and sides. A hard joint acts like a solid conduit. It doesn't absorb or mute the energy. Like hitting a tuning fork on rubber versus on steel. Great analogy. And some advanced UF formulations like one called Ultra CT are specifically designed to eliminate any veneer creep. Really stable stuff. Okay. What else is high performance? Apoxy resins. Usually two-part adhesives, they form exceptionally strong bonds. Better for oily woods.

Yes. Particularly effective for those difficult to glue oily exotic woods we talked about. Yeah. A key reason is their curing process doesn't rely on water. Ah, so no warping. Exactly. Water-based glues can make thin wood veneers swell or warp, which is a disaster. Apoxies avoid that. And interestingly, many epoxy joints can actually be reversed with controlled heat, which is good for repairs. Good to know. Any others?

Polyurethane glues. Also very durable and strong. They cure using moisture from the air or the wood itself. And they have good gap filling abilities. Useful for imperfect joints. Can be, yeah. Fill small voids. And finally, you have dry film adhesives. Like a tape? Sort of. Things like hot melt EVA films or phenyl formaldehyde resins. You might know that as TGO film. KGO film. Sounds familiar. It has a history used in World War II. two aircraft, like the mosquito bomber, for making strong void-free laminates. Void-free meaning no air bubbles or gaps, absolutely critical for structural integrity.

Wow, from warplanes to guitars. Indeed. And fetal formaldehyde resins are also used in modern composite materials like rich light, which you sometimes see used for guitar fingerboards or bridges. So when you really dig into it, the glue line itself is a piece of material science. Absolutely. That hardness, the rigidity of the cured glue. Yeah.

That's paramount for transferring vibrations efficiently. Directly impacts sustain, volume, responsiveness. So every single choice of glue isn't just, does it stick? It's a complex decision impacting the final voice, the sound of that instrument. Precisely. Which brings us right back to Jorma Winkler and his company. Right. Mikei Wood, Hawaii.

Yeah. They've specialized in producing veneers from Hawaiian coa and other exotic woods since 2003. But they don't just sell raw veneer. They offer premium options like paperbacks. which they call cami ply like kami for paper in Japanese exactly and fleeceback called wash me foam so his expertise isn't just sourcing the wood it's about how it's processed and prepared for luthiers to actually use effectively and these pre-backed veneers yeah what's the advantage they must make working with fragile thin wood much easier immensely easier think about

handling a raw wood veneer that might be paper thin it's incredibly fragile i can imagine it just splitting if you look at it wrong. Pretty much. So these backings, the paper or the fleece, they provide crucial stability. They make the veneer much less prone to cracking or breaking during handling and gluing. It enhances workability massively. Which must save Luthier's time and money, reducing waste. Huge reduction in waste and frustration, I'm sure. Streamlines the manufacturing, but... Rather but... Well, it doesn't mean you can just slap any glue on there. Mykai Wood Hawaii provides really specific, authoritative

guidance on adhesive selection and application for their backed veneers. Ah, so the backing changes the gluing equation again. It does. For example, they might recommend a type I pVA glue if you're using a vacuum bag for clamping and waterproofing isn't the main goal. Okay. But if you need

waterproofing, maybe type 2 or 3, PVA and this is critical, they add a big caution. Those types can actually discolor coa wood if you don't apply them very sparingly. He still need precision. Absolutely. Or for their paperbacked veneers, they often recommend contact cement.

But again, with specific instructions, a precise two-coat application, let it tack up just right, and then extremely careful alignment because once it touches. It's stuck. No repositioning. Exactly. Immediate adhesion. So while the backing helps physically, the chemical interaction, the adhesion science, still demands real knowledge and care.

That level of detailed tech. technical support, even suggesting customers practice on cheaper sheets first. Yeah, they do that. It really underscores how critical the adhesives are to getting the high quality results their specialized products promise. It feels like a partnership almost. It really is, a partnership in craftsmanship in material science, and this meticulous approach, focusing on the whole system, not just the wood, it's clearly worked.

Oh, so? Work at Impact. Definitely. Mike Highwood, Hawaii supplies some of the biggest names in high-end guitars. We're talking Taylor Dittars, C.F. Martinenko, Santa Cruz guitar company. Wow, those are major players. The talk tier, as well as pountless individual luthiers around the world, they've really solidified their place in that market. You mentioned Taylor guitars. They seem to have a particular fondness for Hawaiian co-it, don't they?

They do, a very strong affinity. And it's not just because it looks stunning or sounds unique. Although that helps. Oh, it definitely helps. But Taylor has also made significant investments in the sustainability side. like the reforestation Winkler Woods was involved in. Even more directly. In 2015, Taylor Guitars actually formed a joint venture called Siglo Tone Woods.

With who? With another company, Pacific Rim Tone Woods. And Siglo Tone Woods is specifically dedicated to managing and reforesting coa forests in Hawaii. So they aren't just buying the wood. They're investing in the future of the forest itself. Exactly. A major commitment to ensuring a long-term responsible supply of this crucial tonewood. It's quite forward thinking.

It's really interesting. And does this focus on Hawaiian Woods sustainability? Does it reach beyond the big companies? It does, yeah. There's an effort to connect it to education, too. The Hawaii Forest Industry Association started something called the Innovation Plus Imagination Student Challenge, the I Plus I Challenge back in 2017. What does that involve?

They encourage students like high school or college level to design and build artwork or functional pieces using donated Hawaiian grown wood, often including koa and other species. Ah, getting hands-on experience. Exactly. It exposes them to design, to production techniques, but also gets them thinking about the value of locally sourced sustainable resources. It helps foster that next generation of woodworkers, maybe even future luthiers, who really understand these materials from the ground up. So when we step back from all this, what we've really explored today is this incredible, intricate dance. It really is a dance. Between traditional craftsmanship, you know, the Luthiers

skill, advanced material science, like understanding polymode chemistry and glues, and these evolving market demands for unique sounds and sustainable practices. Art and engineering, forest and workshop, all coming together. Yeah. And right at the heart of it, seemingly simple stuff like adhesives. Often overlooked. Yeah. Often seen as just, you know, functional bits. But they're absolutely fundamental. They determine the instrument's structural integrity, its stability over decades. And most critically, as we've seen, it's acoustic performance. They are the unseen forces literally shaping the sound you hear. Amazing. So we want to leave you, our listener, with maybe a provocative thought to chew on. Okay. Consider how all these unseen elements, this meticulous

engineering from, you know, the ethical sourcing of a piece of wood from halfway around the world, to the precise chemical formulation of the glue holding it together, how all that ultimately defines not just the quality, but the actual voice of a musical instrument. Makes you wonder. Exactly. What other hidden sciences, what other unseen choices and materials

might be shaping the everyday objects all around you?