Cat Plug finishing question

Discussion in 'Fiberglass and Composite Boat Building' started by Bullshipper, Sep 19, 2018.

  1. Bullshipper
    Joined: May 2008
    Posts: 106
    Likes: 2, Points: 18, Legacy Rep: 21
    Location: Mexico

    Bullshipper Bullshipper

    I have added resin and talc to my plywood plug and the hull is now 90& true after sanding with long sanding blocks.

    I have some small pinholes I still have to fill so can I proceed in this order?

    Fill pinholes holes with spatula and high build sanding primer
    Sand those spots off with 100 grit on orbital sander
    Spray entire surface with high build sanding primer
    Sand entire hull with with 220 on orbital sander
    wet sand with 600 on sanding block
    rubbing compound too?
    apply 6 coats wax, using 7, and 10 polishers

    The plug has about 400 square feet of surface and I have a 2 man crew
     
  2. Blueknarr
    Joined: Aug 2017
    Posts: 831
    Likes: 159, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    You just block faired to 90% true. Why would you ever consider de-fairing with 100 grit on random orbit?!

    I would change post priming sanding to;
    220 longblock with 400 on the counter stroke.

    To me, high build primer seems soft for moulding off of.
     
  3. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    When you're doing a plug it is imperative that you keep the density of the material you're sanding the same.If you change density with the primer, and go thru the primer to the resin you'll sand in waves. You should sand with an effective longboard not an orbital sander. You should wetsand with 220,320,400 and 600 at a minimum. Definitely use compound. I'm not sure about the compatibility of your "high build primer" with your compound , or wax are you?
    Talk to "ondarvr"-he's a member and and expert on the compatibility of various compounds for plug work.

    ondarvr https://www.boatdesign.net/members/ondarvr.12154/
     
  4. Bullshipper
    Joined: May 2008
    Posts: 106
    Likes: 2, Points: 18, Legacy Rep: 21
    Location: Mexico

    Bullshipper Bullshipper

    Thanks guys. Appreciate your help!
     
  5. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    If you plan on sanding the mold, or using PVA, then there's no need to go to 600 grit or polishing, dry sand it with 320 and call it good, you could still polish it if you wanted though.

    Don't apply or remove wax with a polisher, only do it by hand.
     
  6. Bullshipper
    Joined: May 2008
    Posts: 106
    Likes: 2, Points: 18, Legacy Rep: 21
    Location: Mexico

    Bullshipper Bullshipper

    I am hoping to do as much sanding as a can on the male plug , versus the female mold. I also bought 3 polishers, also with the 3 orbital sanders, so your advice is an eye opener.
    I believe we will be finished sanding with the long blocks and foam backs 1/2 sheet this week using 60 grit.
    Now planning to fill holes with resign and talk instead of bondo, glazing putty or high built primer.
    Than sand by hand again with 150, 300 then 600 wet prior to 5 coats of Johnson pate wax.
    ok?
     
  7. Blueknarr
    Joined: Aug 2017
    Posts: 831
    Likes: 159, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    The issue with power sanders, orbital in particular, is people keep tilting them on edge to focus on problem spots. This replaces a pinhole or scratch with a large bowl.

    When fairing:
    • Use as large a pad as practical to distribute cutting action
    • Do not concentrate sanding
    • Hold block parallel to most prominent curvature of hull
    • Use diagonal strokes (/////////////////////) until entire surface is scratched
    • Sand on counter stroke (\\\\\\\\\\\\\\\\\\\\\\\) with finer grit until first scratches are erased
    • The surface will be sanded into conformity of hard stiff pads
    • Soft squishy pads conform to the surface being sanded
    • Different materials sand at different rates.
    • If a layer is cut thru, then reprime
    60, 150, 300, 600 are large jumps in grit
     

  8. KD8NPB
    Joined: Mar 2018
    Posts: 86
    Likes: 18, Points: 8
    Location: South Carolina

    KD8NPB Junior Member

    Prime / fill with 30 mils of Duratec 707-002.

    Sand up / buff up a section. If the gloss is acceptable, go ahead and prep to pull your mold.

    If you want more gloss, spray your Duratec 707-002, then knock it down with 220 grit. Then topcoat that with their Vinylester Topcoat 1904-45.
     
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