Filling voids in maple burl

[Magnus Geijer]

Found this on that unmentionable auction site while looking for something completely different, and totally couldn't help myself. I've been jonesing to build a solid body anyway, and this seemed like a perfect excuse. A quick google indicates using either black epoxy or the usual superglue-sawdust muck, but I thought I'd check if there were any other ideas out there.

Thanks,

Magnus

[sunburst]

I've tried several "fillers" for burl voids, and the best I've tried has been wood dust and epoxy. All other fillers I've tried either shrank and left low spots later, or swelled and left high spots later. Places that I've filled with dust/epoxy have remained much more level under the finish over the years. It's best to use 24 hour cure epoxy and as much clean, fine dust as you can pack into it. If you try to get more dust into the epoxy and it just stays dry and doesn't mix in, it's about right. I used to make my dust by sanding with 320 grit sandpaper until I saw Frank Ford's trick of scraping the end grain of a block of wood with a chisel (I use a hand scraper rather than dull a chisel scraping with it). It's a quick way to get lots of fine, clean wood dust.

You might want to experiment with some different pieces of wood to see what color the filler will end up, it's darker than the wood that you make if from, and maple can be mixed with walnut (for example) to control the color, or dyes can be added. Once the dust/epoxy filler is made, pack it hard into the voids with a stiff putty knife or the like. Keep packing and pressing until you're sure the voids are completely filled.

I don't recommend dust from around the belt sander or any "found" dust like that, though some people use that sort of thing. It's too coarse, too dirty, and too multicolored to look good when used as a filler.

[Woody Turner]

I agree with sunburst that a little experimentation on scrap is in order. The bark inclusions just outside the template outline would serve the purpose. I'm not sure, though, that I would opt for sunburst's use of pure/uniform sawdust for the filler. With that approach you'll wind up with a patch of homogeneous color against the wild pattern of the burl. The repair may wind up looking like wood putty. What I've done in my work with burl--not musical instruments, though--has been to mix shavings and dust into a composite fill, sometimes in a swirled pattern. If I take care, the repair sometimes looks like another whorl in the overall burl pattern. Again, if you try this, do experiment first.

[sunburst]

That's probably good advice. I've never filled any voids big enough for making faux swirls with shavings, only small voids.

[Magnus Geijer]

Thanks, that makes a lot of sense. Thankfully the outline in the picture is a regular guitar Strat, placed on there by the seller, so my mandolin outline will be quite a bit smaller, so there should be a goodly amount of spill pieces for filling practice.

This is the first time I've so much as held a piece of burl beside veneers, and boy is it different. It feels more like some kind of dried out sponge than wood. Previously I had plans for making a back for a regular acoustic mando out of this stuff, although perhaps with some reinforcement, but this stuff is so soft and unstable that now I'm concerned about how it will hold up just as a drop top. Sure is pretty, though.

/Magnus

[Woody Turner]

"...drop top"??? You would use this as a top? On stability: some burl is unstable, but a lot is quite stable because the grain goes in all sorts of directions, with the dimensional changes along various axes canceling each other. If you do opt for acoustic mando use, you may want to wait a long while (weeks) after you resaw to approximate thickness, just to make sure stability won't in fact be an issue in the finished product.

[Woody Turner]

Also, to strengthen/harden punky wood, consider thin cyanoacrylate (Crazy) glue for spot use or Polycryl Wood Stabilizer for global application. You can get both products at www.woodturnerscatalog.com. (nfi)

[dunwell]

Something that I've used on large(ish) voids is to mix various grades of material in with the epoxy. The usual is to just use some medium or coarse sawdust of a matching wood and this works well for smaller voids. However, when the filled area gets larger, then it's texture becomes an issue. The epoxy tends to over-power the fill material and it gets a plastic glossy look that tends to catch the eye.

I have found that if I mix medium and coarse sawdust and then add in some crushed up shavings that it works best on larger voids. I just use a block plane and take some very fine cuts off a scrap piece and then crumble those up a bit. I also find that adding in a bit of coarse ebony or mahogany sawdust adds even more of a contrast "texture" to the fill material. I goober all this together with a tinted or clear epoxy and then force it in with some dental tools leaving it proud of the surface. Then after it is hard cut it back with a glass slide or scraper.

The result is a much more multi-contrast fill that doesn't catch the eye as much as the straight fill. As always, do some test fills on scrap to find the blend of materials that best matches your specific fill location.

FWIW,
Alan D.

[sunburst]

This probably isn't a good idea for large fills, but for small fills in wood that is to be finished like an instrument (lacquer or varnish), I usually draw wood grain on the fill with various colors of ink. that can make even stuff like Elmers Carpenters Wood Filler look pretty good, but the dust/epoxy is still the best filler I've tried as far as remaining level under a finish.

[Magnus Geijer]

Sorry, drop top may be a misnomer. It'll be the top layer of a solid body, glued to an inch-and-a-half think alder body, there will be no structural requirements on the burl. I'm just concerned about keeping it from getting too dinged up.

So it sounds like should basically sweep the shop floor and mix it up as unevenly as possible. Completely opposite of what I would have done if I hadn't asked, but makes perfect sense. This should be fun!

Thanks,

Magnus

[Desert Rose]

Magnus

Your use of the term drop top is quite good.

Its apiece of decorative wood up to about 1/4 inch thick glued on a thick blank to make an electric guitar body

The thing that makes it fit the drop top name is that the front is contoured on the body blank and the deorative wood is bent to form this, thus the drop top as on a Strat body contour

Scott

[David Houchens]

Somethng I've done in walnut burl on banjo resonator backs is to copy the shape of the void to be filled. Then search around the unused part of your burl to see if you can find a spot where you copied pattern looks similar to a pattern of burl. Cut a little proud of pattern and inlay this piece of burl in the void. I'll agree this is a little easier to hide in walnut, but if done well it can look very nice. Again, practice in a unused void. David