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Compound Used For Filling & Smoothing Joints For DIY Speaker Boxes?

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  • Compound Used For Filling & Smoothing Joints For DIY Speaker Boxes?

    Dumb question, what is used to fill in the joint lines/gaps in diy boxes? Wood Dough? Or is there sometnig better? I want to paint over the MDF without any hint of joint gaps. Thanks, guys!
    Jazz Wine HiFi

  • #2
    Wood filler works, but takes some time and possibly a few passes. Automotive Bondo works really well, and fast, but is messy.

    It also depends on how you're finishing. A glossy finish will require a whole lot more attention than Duratex. With Duratex you can even use wall putty for a super quick fill.
    Electronics engineer, woofer enthusiast, and musician.
    Wogg Music
    Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

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    • #3
      Automotive glazing and spot putty works well too. Use right out of the tube.. no mixing.

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      • #4
        I think the bondo, woodfiller, spot putty, etc. work well for the gaps.

        For joint lines, it is harder and there are a many threads about possible treatments. The simplest seems to be a thin coat of glue (yellow wood or Elmer's white / with or without 50% water) but there seems to be lots of opinions and disagreements. One of the issues is that the seam can "ghost" even years later, so that what "seemed" to work for someone on their latest build isn't necessarily reliable because not enough time has passed.

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        • #5
          Bondo works well from what I've heard, but once you open the can the unused portion is good for about a year. I've also heard exterior spackle is good, but I haven't tried it. It's a bit less expensive than bondo since you can get just the amount you need.

          What size saw do you have? If you have a saw with a large enough table, and provided the boxes aren't really large, you could cut a kerf in the middle of the gaps and fill the kerf with scrap wood strips that you've prepared.

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          • #6
            Nothing works, in my opinion. Tried Bondo and glazing compound. Tried glue. Highly recommend not adding more water to the equation. If you want a high gloss finish you will need to put veneer or something over the joint, or use mitered corners.

            Recently built two subs from PE kits. I filled everything with drywall compound after two coats of BIN shellac based primer. That primer is absolutely excellent for mdf and I'd use it under whatever filler you use. The drywall compound appears to be working but I'm just using eggshell paint for some subs in the corner. I'm accepting a level of finish which would be nice for architectural trim work but low for a commercial product.

            The mdf you buy from home Depot or whatever is really soft on the inside and soaks up moisture readily. The stuff PE uses for kits is much nicer.

            I used Bondo on a build and completely coated the edges. They're visible now a year later. More goop is simply not going to solve the problem. Fiberglass mesh might help.

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            • #7
              Dave Pellegrene "trench method". Textured paint or veneer needs much less work.

              Continuum Speakers Using my Trench Method on the MDF Seams - Techtalk Speaker Building, Audio, Video Discussion Forum

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