Compound to fill and fair plywood bulkhead?

Discussion in 'Materials' started by andysailor, Dec 10, 2018.

  1. andysailor
    Joined: May 2017
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    andysailor Junior Member

    Need to make a flat surface om my bulkheads. Some are because of veneer that has come loose. The remaing veneer seem to sit good. Other dents are from drill holes, repairs, egg....they do need lots of work to get fair.

    Epoxy filler necessary? Or some simple wood filler? Wood is untreated in many places.
     
  2. Deering
    Joined: Feb 2005
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    Deering Senior Member

    Sounds like an epoxy fairing compound would be in order. Most of the manufacturers offer products specifically for that purpose. I’d be a little concerned about any loose veneer. That would either need to be glued down with epoxy or removed.
     
  3. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Epoxy filler necessary?
    Epoxy fairing compound would be the most worry free. As bulkheads aren't usually submerged, polyester fairing may be used. It will have the same poor adhesion to the raw wood as polyester resin.
    Or some simple wood filler? Most simple wood fillers don't hold up in marine environment. They have even poorer adhesion than polyester. The filler in a hole will often separate from the sides but remain in place with a ring crack.
    Wood is untreated in many places. Epoxy has the greatest adhesion to raw wood.

    If any veneer is lifting, then there's a whole lot more about to.

    Chanfer the drill/screw holes with a counter sink bit to prevent ring cracks.
     
  4. andysailor
    Joined: May 2017
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    andysailor Junior Member

    Im doing a total refit on the interior and will cover the bulkheads with either Formica or some kind of vinyl film. With the vinyl film.the surface needs to be spotless.

    How about using epoxy resin to wet out the wood. Wait for it to get tacky....and apply polyester filler?
     
  5. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    Wetting out the areas to be filled is a really good approach, will do much to help your filler to bond.
    I’d likely do the patching with polyester, as it’s non-structural work.
    Bondo would probably do just fine, still a good idea to pre wet, though.
     
  6. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Poly bonds to raw wood better than it bonds to epoxy. Bondi will adhere to waxed paper better than it will adhere to fresh epoxy!

    It is highly unlikely for properly mixed epoxy to have issues in this project. Epoxy will definitely succeed.

    Poly might have issues with existing finish. Poly can bond to wood. BUT often it doesn't. Poly resin should bond better than Bondo. Poly will shrink more than epoxy, so give it a few days to shrink up before fairing. It is almost impossible to mix the exact same percentage of catalyst in every batch of poly fairing. They will probably shrink and sand differently. They'll sand smoothly if not absolutely fairly.
     
  7. Sparky568
    Joined: Jan 2017
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    Sparky568 Junior Member

    Polyester will work just fine, it would also be the most economical and easiest to fair to a smooth surface. As bonding to wood issues go, whether it’s epoxy, poly, primer or paint it is all in the preparation. I would remove anything that wasn’t wood or actual fiberglass. Grind, heat, scrape whatever it takes to get to a good base. Well applied polyester based resin applications can last a lifetime like most boats that are made from it.

    Sand with 40 to 80 grit. Clean with acetone till a wipe reveals a clean rag. If you go all the way down wood you should “hot coat” it by applying resin only directly to the wood with maybe a 5% dilution of acetone to thin out slightly. Couple coats of this then apply a layer of mat. You can then apply polyfair or some equivalent after the mat becomes tacky. Or you can let it cure and sand to a reasonable smoothness. The polyester fairing compound will “set” rather quickly so be careful with catalyst ratio. Personally I use from slightly less than 1% to 1.5% max. Apply in thin coats and sand if needed.

    Sand with gradually increasing grit till you get a finish you are happy with. Final sand is 80 grit to give whatever finish you use a good bite. Depending on the square footage and skill set could easily be a weekend job. Best of luck.
     
  8. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Getting a fair and even surface finish is always a pain. Some sort of glue on veneer is way easier, even if you make it yourself with FG on a flat melamine panel.
     
  9. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    1 Epoxy 60 minute ~3 oz will be a lot
    .75 cabosil
    1.5 microballoons

    By volume.

    Mix epoxy for one minute; add dry and mix until it starts to ball.

    Mix on a board with 4" trowel and add more dry ingredients until the mix is stiff enough to stand up on its own.

    Keep mix flat on the board or it may kick early.

    A few of these other guys might have the ratio down better.
     

  10. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Sand.
    Refill missed spots
    Sand again.
    Vacuum
    Tape edges and cover close surfaces
    Undercoat
    Sand again
    Paint
    Paint final coat
    Remove tape and covered surface
     
    fallguy likes this.
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