Torrefied Wood - Luthier Tips du Jour Mailbag
In this episode, luthier Robbie O’Brien and mandolin builder Geoff Burghardt talk about torrefied wood.
Video Transcription
[on-screen text reads: Luthier Tips du Jour Mailbag]
Mailbag question: Will torrefied maple behave like regular maple, and is it more difficult to work with?
Robert O'Brien: Today's Tips du Jour Mailbag question comes to us from Texas. "Robert, I'm thinking about using torrefied maple for my next mandolin. My concern is, will it behave like regular maple and is it more difficult to work with? Jason in Victoria, Texas."
First of all, let's talk about what the word means, torrefaction, and that is submitting a piece of wood to a heat process under a vacuum, a high heat around 300 degrees. And the vacuum is to keep it from catching fire because it's going to catch fire around 400 degrees, so you're removing the oxygen from the process. And what it's doing is basically in a nutshell, artificially aging the wood. So that's kind of the definition of what that means.
Now, recently I received some really nice quilted maple that had been submitted to this process, and I gave it to master mandolin builder, Jeff Burghardt. Now, recently, Jeff and I finished an online mandolin building course, and I wanted him to have the opportunity firsthand to work with this wood. So let's talk to Jeff about his experience working with this wood.
Geoff Burghardt interview
Okay, so here I am with mandolin builder, Jeff Burghardt, and recently I gave him a piece of this maple, and he had a tough time with it, didn't you?
Carving and sanding
Geoff Burghardt: Well, I had a great time and had a tough time. It kind of depended on the process, yeah. I found it to be really easy to carve. The grain, whatever the torrefaction process does to the grain. Didn't have as much of an issue with the quilted maple of chipping out or the wood acting spongy under the chisel. So that part was nice. It sands really nicely, almost like cherry or mahogany. I mean a lot easier than the regular quilted maple that I've worked with. That was the easy part. The hard part was the bending. I just could not get this stuff to bend. And so-
Robert: No way, no how?
Geoff: Well, no. So here's a little example. I got this. It's kind of hard to see. You got about-
Robert: Holy cow. Yeah, look at that. That stuff is brittle.
Geoff: Yeah.
Robert: Wow.
Geoff: So in doing this, I did a lot of research and I found that people had remarked that the wood is more brittle, it's more dry. And I certainly found that to be the case. I even soaked the wood for 24 hours and got it on a hot pipe and still couldn't get it done.
Robert: Still wouldn't go.
Geoff: I got it down to about a millimeter, just over a millimeter or so.
Robert: Right, thinner than what you normally go.
Geoff: Way thinner than what I normally do.
Robert: Still wouldn't go.
Geoff: And it still wouldn't go, it would just break. So unless someone has some magic pill, I found bending the wood to be very difficult. So for me, I'm going to use the back that I carved, but for the sides I'm going to just use regular quilted maple, and I'll either stain them to try and match or I'll just leave them. And then the torrefied will really be sort of magnified in that way.
Glue joints
Robert: Right. Now, let's talk about a couple of other things. I think during your research, you said you had some glue joint issues or found out some things about gluing this type of wood together.
Geoff: Yeah, so I learned that some people said they were having a hard time with hide glue and gluing the wood together. I use Tightbond, and after I had cut my piece out to shape, I flexed this joint here to see what would happen. And it broke right on the glue joint. There's a couple little pieces, but it didn't break along the grain outside of the glue joint the way I normally would expect a normal glue joint to do. So does that mean it's prone to fail? I don't think so. It took quite a bit of pressure to break it, and when I went on to carve the back, I was beating it pretty hard and had no glue joint failure there. But this is a matter of overtime over years. It's hard to say what's going to happen, but certainly people have reported issues with glue joints and torrefied.
Finishing differences
Robert: Okay. So Jeff, how about when it came to finishing? Was there a difference?
Geoff: Yeah, that's a good question. Some of my research, and I'd recommend you look up this process, it's pretty fascinating and see other people's issues. Some people are saying they had trouble with the finish sticking, and so I usually do shellac and/or true oil combination. So I worked up this piece here and I did shellac on this side, basically French polish, rough French polish, but a French polish. And over here I did true oil and I did a light, light and polish on top with shellac. And so I think the true oil helped pop the grain a bit more, but I've had zero issue with the finish sticking to it at all.
Robert: Right, so you had no problem?
Geoff: So it could have been whatever the finish that these people were using, lacquer, catalyze, whatever, but if you stick to shellac and oil and true oil, at least, in this case, it worked out just fine.
Robert: Perfect.
Geoff: Yeah.
Tonal differences
Robert: So basically the reason for using this type of wood, some people say ages it. And so I imagine that the benefit would be tonal. Did you notice a tonal benefit of using this wood?
Geoff: It doesn't sound all that different from regular quilted maple. I mean, I would certainly use it, and this is the back that I carved so far. Right now what I have is a little bit thicker than my normal graduations and around the same amount of flex, of stiffness, that I normally go for. So I might take it down a little bit more, but it feels this particular wood, this piece, feels a little bit less stiff than the other ones. Based on what people talk about with the process, with hardening up the cell walls, it seems like it should make it sound older and better, but I think that's just cause to do another video once this thing is on a mandolin, and then we can talk about what it sounds like there. But I don't think it's a bad thing at all. I think it's worth investigating.
Robert: Sure. Now, of all the experience you've had over the last week or two with this type of wood, would you use it again?
Geoff: I think I would. I would like to find a way to bend it. I would. I mean I would dip it in gasoline if it's... Yeah I do, but that's probably a bad idea.
Robert: Yeah, don't try this at home.
Geoff: Don't try that at home. Yeah, that's a hesitation. I would really love to be able to bend it and get a complete back and side set out of it. If it's just going to be the back, I mean, once this is together, if it makes a killer mandolin, I'm pretty sure it will. Then I would certainly use it again. Probably won't be my mainstay, but something worth it. If someone wants an interesting mandolin with an interesting story, I think it would be totally worth consideration.
History of torrefaction
Robert: So as we're talking here, Jeff's told me an interesting story about where this process actually came from and a little bit about the history of it. Why don't you try and tell us about that Jeff?
Geoff: Yeah, so I mean, when I was doing research on other people's experience with this, I saw threads going back to 2004, perhaps even before that. And there are people that even cite Viking battleships. They used some smoke process to help harden up the wood that they used on their ships. I think torrefaction commercially became big when they were trying to make a product that could handle deck, being in decks and being outside insect rot resistant is where it came from. But as people looked into the cell structure and what it did to the wood, they thought, "Oh, let's try some instruments out of this."
Robert: So if you build an instrument with this, a mandolin, for example, the bugs won't eat it.
Geoff: The bugs won't eat it, which is good.
Robert: Perfect.
Geoff: And because it won't bend, you can't build a banjo out of it, so the bugs will eat the banjos instead and we're okay with that.
Robert: We're okay with that. All right. Seriously though, Jason, thank you very much for your question.
Geoff: Good question.
Robert: I hope this has been enlightening. And by the way, if you want to learn how to build a mandolin, Jeff and I just finished an online mandolin building course, where it takes you from beginning a box of wood, all the way to a finished product. So if you want to learn how to do that, check out Geoff Burghardt at obrienguitars.com and you can check out his mandolin building course. And thank you very much.
[on-screen text reads: More Luthier Tips and online courses available at www.obrienguitars.com. Private and small group guitar building and finishing instruction available.]
