Help with scratch repair in older gelcoat

Discussion in 'Fiberglass and Composite Boat Building' started by bch, May 20, 2019.

  1. bch
    Joined: May 2019
    Posts: 2
    Likes: 0, Points: 1
    Location: Vancouver, B.C.

    bch New Member

    Hello,

    I have decided to do some repairs in my gelcoat and ran into an issue.
    The gelcoat is in good condition, but has yellowed due to age and UV. I successfully repaired some scrapes and scratches by colour matching, however, when I sand the area to level it, the existing gelcoat around the repair gets sanded as well and becomes much whiter (the yellowed part is sanded off). So I am left with smooth, nice looking repairs but the entire repair area is a whiter spot along the existing beige gelcoat. I am wondering what the best solution to fix this is:
    • Wet sand entire hull to remove the yellowed gelcoat. Tried a test spot but it required lots of sanding with 400 grit to get through the yellowed area. Would be a ton of work and I am worried I will thin the gelcoat too much.
    • Leave it alone and hope the whiter area becomes faded with time.
    • Use a product to whiten the gelcoat (oxalic acid). I have heard that products are usually for yellowing due to growth and sitting in the water rather than from UV.
    • Something else?
    Any tips are much appreciated!
     

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  2. Blueknarr
    Joined: Aug 2017
    Posts: 891
    Likes: 175, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    Welcome to the forum

    Ouch tuff break.
    Color matching gelcoat is tough art.
    What you do now depends on how cosmetic councous you are.

    You are correct to worry about cutting thru the gelcoat. I would be hesitant to do much more sanding on it.

    The white gelcoat you have exposed is still partially degraded by UV. It won't take long for it to yellow back to where you began.

    Acid may help but probably not. Certainly won't hurt.
     
  3. ondarvr
    Joined: Dec 2005
    Posts: 2,312
    Likes: 248, Points: 63, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    This is always the problem with repairing aged gel coat.

    You can either do the enitire hull to make it look right, buy stickers to cover the area, or live with it as is.
     
    Last edited: May 21, 2019
  4. bch
    Joined: May 2019
    Posts: 2
    Likes: 0, Points: 1
    Location: Vancouver, B.C.

    bch New Member

    Thanks for the replies guys, this is my first time doing cosmetic gelcoat repair.

    By this do you mean wet sand, buff, and polish?

    Cheers!
     
  5. Blueknarr
    Joined: Aug 2017
    Posts: 891
    Likes: 175, Points: 43
    Location: Colorado

    Blueknarr Senior Member


    That and possibly re"painting" everything.

    One of gelcoat's problems is that it is not cromaticaly stable. It is not unusual for gelcoat to fade differently on one hull. I have had to tweek a color match into five different shades for one boat.
     
  6. ondarvr
    Joined: Dec 2005
    Posts: 2,312
    Likes: 248, Points: 63, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member


    Yes, you’ll need to do the entire hull for it to match.
     

  7. Zippydoodah
    Joined: Jun 2019
    Posts: 8
    Likes: 0, Points: 1
    Location: Christopher, IL

    Zippydoodah Junior Member

    I would see if a light grit compound would help. It would be faster.
     
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