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Thread: Wet Sanding and wood swell - Opinions?

  1. #1

    Wet Sanding and wood swell - Opinions?


    I have a basswood guitar body and it is almost time to commence wet sanding of my clear coat.

    However, I've read online that water can cause unpainted areas of the guitar to swell and overtime, cause damage. Eg. around areas such as bridge post holes, pickup pockets etc.

    Is this true? What are people's experiences? Could you substitute water for another liquid to lubricate sanding? Would a mineral or plant based oil be OK?


  2. #2
    Overlord of Music Sonic Mountain's Avatar
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    Jul 2017
    Toowoomba, Qld.
    You just need to be extremely careful not to let the water get onto any unpainted areas. It will swell the wood and wreck your finish. I normally have a towel handy and sand a bit then immediately dry it off. You can also block off holes with toothpicks or similar which helps a bit. It is also possible to just dry sand with a very fine grit paper - but you'll use a lot of sandpaper as it will clog pretty quickly. If you use a decent cutting compound prior to polishing it can remove the need to spend too much time sanding flat, but you'll need an electic buffer of some kind to get the best results.
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  3. #3
    OK thanks....So I'll need to be extremely careful then!

  4. #4
    Here's a couple other options I use.

    1) "painting" shellac into the holes with a small artists brush (5-6mm one, not the teeny-tiny ones). 3-4 coats or until you see some build-up. It dries really quickly so you should be able to get it done one day and wet sand the next.
    get the sides as thoroughly as you can without getting it on the finish on top. If you do, you can wipe it away with bit of rag if you get to it quickly, and a tiny bit will be covered by pickup rings etc. This works particularly well with the large holes like pickup route and control cavities.

    2) plug the holes (like the bridge post holes) with non-absorbent material. After I pack the hole (I use balled up painters tape) I make a little "cap" by cutting the painters tape to fit over the top of the packed material so it goes as close to the edge of the hole as possible. doesn't need to be perfect, but best as.
    You can wet sand right over the plugs without catching them with the sandpaper.
    Of course you can also combine both these methods.

    And like Sonic said, keep a dry rag/towel handy to mop up as you go so the water doesn't puddle anywhere for too long.

    I presume you're talking about the RC-1 Custom kit you were/are building. If that's the case, one thing I noticed in your build diary, is you masked off the pickup routes when you painted. When I spray the finish, I spray right over (into) the pickup routes. This seals them and prevents having to worry about water problem when wet sanding.
    Making the world a better place; one guitar at a time...

  5. #5
    Mentor fender3x's Avatar
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    Jan 2016
    Miami, FL, USA
    I have heard that some people wet-sand using alcohol rather than water because it evaporates much more quickly and doesn't swell the wood as much. I am nervous about using it with a finish, however. Poly is pretty had to damage, but alcohol is a pretty good solvent...

  6. #6
    Mentor fender3x's Avatar
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    Jan 2016
    Miami, FL, USA
    ...So I tried to do a little wet sanding using isopropyl alcohol rather than water on acrylic test piece that had been curing for a bit over a week. I don't think it caused the finish to dissolve, which is the good news, but it made the material it removed clump. Won't use it again over finish. It did not do any real damage, but I am still glad to have tried it on a test piece first.

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