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Spalted Maple Tops & Control Cavities

Discussion in 'Luthier's Corner' started by Lonnybass, Dec 21, 2014.

  1. Dec 21, 2014 #1
    Lonnybass

    Lonnybass

    Jul 19, 2000
    San Diego
    Endorsing Artist: Pedulla Basses
    Hey gang-

    I'm about to start a bass using a highly figured spalted maple top.

    Obviously the laminations will need hardening/stabilizing treatment for structural integrity.

    Given these strength considerations, I'm most concerned about the area of the control cavity and where the pots will be mounted to the wood, as this is always the single thinnest wood component of the instrument. What approach have you guys taken to make sure the cavity floor doesn't just crumble away? Will epoxy stabilizing treatments harden the spalt laminates to the point where they are completely solid?

    Curious to get everyone's thoughts - thanks!

    Lonnybass
     
  2. Dec 21, 2014 #2
    Bruce Johnson

    Bruce Johnson Gold Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    I'd play it safe and cut a plate from 0.063" aluminum that covers the whole "roof" of the control cavity. Epoxy it up in there. Structural reinforcement and it can be part of the shielding, if you connect to it electrically. Spalted maple has structural properties similar to a wheat cracker. If you don't reinforce it, you'll break it putting the knobs on.

    Yes, you should stabilize the spalted maple anyway, to seal it up and keep it from denting and wearing. I normally first coat it with CPES (aka Smith's
    MultiWoodPrime), which is a water-thin epoxy made for sealing up rotted wood. Which is what spalted maple is. Then dab on several coats of West Systems epoxy to fill the grain up to the surface and harden it. Sand that back level, and do what you want with the finish. Still weak structurally, but better than it was raw.
     
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  3. Dec 21, 2014 #3
    Lonnybass

    Lonnybass

    Jul 19, 2000
    San Diego
    Endorsing Artist: Pedulla Basses
    Bruce, thanks so much, I've learned a lot from you over the years and really appreciate your suggestions about working with the spalt. I will definitely reinforce the inside of the control cavity. I did something similar a few years ago on a burled redwood bass, using a thin slab of polycarbonate.

    Do you do the stabilization work before you do any machining or routing of the laminates? Just curious how essential it is to do early in the process instead of before applying finish. Thanks in advance!

    Lonnybass
     
  4. Dec 21, 2014 #4
    Bruce Johnson

    Bruce Johnson Gold Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Lonny;
    I would first use West Systems epoxy to glue the spalted maple down to the body wood. Just rough saw the edges, leaving some extra. Then do the CPES and West Systems treatment on it to toughen it up. Then do your perimeter routing, pickup openings, etc. The epoxy will help prevent chunking. When the body is shaped and into the sanding stage, go back over the spalted top with some more epoxy as needed to fill any soft spots. The West Systems will also work very well as a grain filler on the main body wood, if needed.
     
  5. Dec 21, 2014 #5
    Lonnybass

    Lonnybass

    Jul 19, 2000
    San Diego
    Endorsing Artist: Pedulla Basses
    Makes good sense Bruce. Great input. At this point I'm most concerned about maintaining the integrity of the cavity where the two switches will be installed, as they typically have such short threadings and require such a thin mounting surface. Maybe I'm just worrying too much, just don't want to take any chances with structurally weak areas.

    Here's the top in question (note: the Les Paul outline is just a sample markup from the sawmill).

    Spalttop_zps63c6f7e3.jpg
     
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  6. Dec 21, 2014 #6
    JustForSport

    JustForSport

    Nov 17, 2011
    That's pretty!
     
  7. Dec 22, 2014 #7
    Bruce Johnson

    Bruce Johnson Gold Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    To reinforce the mounting of the controls, use the aluminum plate, as I described above. That's the simplest and surest way. Spalted wood is beautiful, but it has almost no structural strength. It's a wooden sponge.
     
  8. Dec 23, 2014 #8
    Lonnybass

    Lonnybass

    Jul 19, 2000
    San Diego
    Endorsing Artist: Pedulla Basses
    Bruce-

    Speaking of the epoxy stabilizing treatment for the spalted maple - what is your preference for a protective topcoat these days? I've used Benjamin Moore gloss varnish for the past 7 years or so and it's worked well enough, but the long cure time and limited scuff and wear protection has me looking into some other options. I've seen a few threads mentioning Varathane from Lowe's as well as some of the General Finishes products, would love your thoughts. I'd used Minwax poly a long time ago and would just as soon never use that stuff again, but ironically the bass it was applied to still shines like brand new! Looking forward to your thoughts - thanks much.

    Lonnybass
     
  9. Dec 24, 2014 #9
    Bruce Johnson

    Bruce Johnson Gold Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Lonny;

    Look on that Target and Varathane thread. I'm one of the contributers. I've recently been working with the water-based Varathane Floor Finish, and I love it so far. With a little more experimenting, we'll get the process figured out. I think it's the ultimate finish for us small Luthiers.
     
  10. Dec 24, 2014 #10
    Lonnybass

    Lonnybass

    Jul 19, 2000
    San Diego
    Endorsing Artist: Pedulla Basses
    Bruce, will do. I've actually already started looking through that thread, lots of good stuff in there. I'm excited to try the Varathane.

    Lonnybass
     
  11. Dec 26, 2014 #11
    Means2nEnd

    Means2nEnd Supporting Member

    Jun 27, 2010
    Prana Custom Guitars - Mountville PA
    I have learned almost everything I know here on luthier's corner. I am no Bruce for sure and I haven't updated my two build threads but I am finishing up two bodies and I have one with a buckeye burl top and I do have a 2mm black fiberboard that's stabilized but will still be weak. One thing I am doing with that bass is recessed area for the knobs. I think it's a great attention to detail and I think it looks fantastic on PRS and Les Pauls. So I customized a tool for my drill press to get them done easily with rounded bottom edges. I did a test run yesterday and only need to sand around the top where the recess meets the top. This will keep the top as thick as possible and will only be at it's thinnest right where the pot is screwed in. I still like the aluminum idea I'll gladly "borrow" that from Bruce as well.
     

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