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Help With Gelcoat In Fish Mold

Discussion in 'Molding and Casting' started by 1stturkey, Jun 9, 2021.

  1. 1stturkey

    1stturkey Member

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    I'm trying to follow Gary Bruch's "Molding & Casting Fish" article in Breakthrough issue 85 but am not certain I'm using the gelcoat right. The stuff I bought (Marine Evercoat) is pretty thin. I added about 12 drops of catalyst for the few ozs of gelcoat and poured it into the mold but it never completely hardened, even overnight. Also, I'm not sure if this is supposed be set up before proceeding with adding the fiberglass chop and resin to strengthen the body. The article mentions gelcoat can be made thickening resin with cabosil. This sounds cheaper than gelcoat itself.

    Did I just not add enough catalyst to the gelcoat or is the Marine Evercoat the wrong stuff. Was almost $70 a qt thru O'Reilly's.

    Any help is appreciated.
     
  2. Frank E. Kotula

    Frank E. Kotula master, judge, instructor

    There could be a lot of factors in this
    Moisture
    Not enough catalyst
    Age of gel coat
    You might get it to set up by mixing a hot batch and going over the semi set one but it may not work depending on what’s going on between the fish and the gel coat.
    I always seal them first with lacquer before I do a gel coat to seal in moisture.
    You might have to scratch it off and start over if the fish is ok or try your luck on another one. Sometimes things get omitted when we write things down for publication
     

  3. 3bears

    3bears Well-Known Member

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    I'm no expert here but you are trying to make a cast from an already poured mold, right? Here's my experience with gel coat and it's somewhat limited in casting. If you do not get it mixed up properly it can take forever to set, it almost seems like gel coat without hardener with set quicker. Also not enough hardener, which this sounds more like your issue, will cause this. I'n one of my previous career, auto body, when using chop it got embedded in a wet coat of gel and then smoothed over with more gel. When it comes to strengthening a cast I would think you want the outer layer, detail layer to set up and then spread another tack layer of gel to that and then embed the chop into that.
     
  4. 1stturkey

    1stturkey Member

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    Thanks for the help guys! Yes, I'm pouring into a bondo/resin mold sealed with PVA. The gelcoat was just purchased so I probably just didn't add enough catalyst/hardener.

    I removed the cast bullhead that didn't completely harden and will reseal the mold and try again with a "hotter" gelcoat mixture.

    Appreciate the feedback!
     
    Frank E. Kotula likes this.
  5. Mudbat

    Mudbat Well-Known Member

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    I don’t use gel coat just bondo/resin. Gel coat costs to damn much these days!
     
    1stturkey, Terry Bennett and 3bears like this.
  6. 1stturkey

    1stturkey Member

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    Thanks, Mudbat! It really is crazy expensive. The article even states you can "make" gelcoat with resin and cabosil. I'm gonna try that too.
     
  7. crablover

    crablover Well-Known Member

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    Turkey, resin and cab o sil mixed is not gel coat! True gel coat contains titanium dioxide. The heat people talk about is not going to happen when your gel coat or resin is spread so thin. Only in bulk will heat be created. Your gel coat needs to be wax free and the MEKP that comes with resins is usually bad because it is photo chemically reactive and sold in clear tubes. Get some good MEKP like High Point 90 and keep it in the refrigerator. If you still have the fish coated, take it out and put it in the sun or under UV light. There is so much misleading information posted about fiberglass resins, like adding both hardener's to a bondo resin mix, and that resin and bondo is gel coat. NOT! Get some good quality MEKP, coat your part and set it in the sun. If you do not see a color change when adding your hardener, you have not added enough
     
    1stturkey likes this.
  8. 1stturkey

    1stturkey Member

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    Thanks, crablover! Appreciate the excellent information!!
     
  9. 13 point

    13 point Well-Known Member

    Crab lover knows what he is talking about he does a lot of glass work. I would follow what he tells you for a superb product.
     
    1stturkey likes this.
  10. Mudbat

    Mudbat Well-Known Member

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    Yeah I’m not pretending it’s a gel coat. It’s bondo and fiber glass resin.
     
  11. 1stturkey

    1stturkey Member

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    Thanks again for all the help guys. Not enough catalyst in the gelcoat was the problem. Solved that and have been casting away making a couple casts of the bullhead - trying to use the gelcoat before it's shelf-life is gone. I didn't realize Cabosil has a limited shelf-life too.
    Anyway, gelcoat is crazy expensive so I might try Mudbat's method sometime.
    Now I need to work on getting a better seam line...
     
  12. crablover

    crablover Well-Known Member

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    Cab o sil should not have a shelf life at all as it's made to absorb the resin unlike talc in bondo. Bondo's filler is talc to make sanding easier. Micro balloon's, Cab O Sil etc. absorbs the resin into a monolithic bond, creating a much stronger part over bondo. Fiberglass resin is also not waterproof but true gel coat is. Bondo and resin although not gel coat does work however it is far more brittle and not as strong as gel coat. Bondo and resin will not work for long term production molding and will chip and crack from undercuts and stressed areas of your mold. Bondo also has wax that rises to the surface as it cures. This wax can cause issues in the layup of cloth or strand layering. For a very strong production mold true gel coat should be used backed up by cloth or strand or a tooling gel coat. One of the biggest mistakes when molding and casting is using both gel coat and resin that contains wax. All your resin materials should be wax free and use a good quality MEKP like High Point 90.
     
  13. 1stturkey

    1stturkey Member

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    You are the man, Crab! What an awesome education you are giving me. I really appreciate the detailed explanation of the differences of the products. Thank you very much!!

    As for the Cab o sil shelf life...what I got from McKenzie/Vandykes is a Smooth-On product called URE-FIL 9 fumed silica. The label has in bold: Important: Limited shelf life. Use as soon as possible. Maybe it's not Cab o sil exactly but according to the label it is fumed silica.
     
    Last edited: Jun 19, 2021
  14. crablover

    crablover Well-Known Member

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    Turkey, you are using the wrong filler for fiberglass resin. URE-FIL 9 is a thickening agent for rubber and silicon molding. Being silica based, it's shelf life is caused by moisture saturation from the air. You need to use a resin filler like Cab-o-sil or Micro Balloons instead. Get the proper filler, and a better MEKP. Keep your MEKP in the fridge, and when you add it to your resin and mix, you will see a color change in the resin. If you don't see that change, you need more hardener. You can speed up the setting time of your catalyzed resin by exposing it to UV light. Mix up a test batch of your catalyzed resin and brush it on two pieces of cardboard, then set one in the sun. Check back to both pieces in 15 minutes and see which one has fully catalyzed. Hope this helps!
     
  15. 1stturkey

    1stturkey Member

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    Dang it! I told Mckenzie I wanted Cab o sil but Ure-fil 9 is what they sent me. I'll have to call them back and ask why. Probably that's all they carry and most guys (like me) wouldn't know the difference.
    Thanks again, Crab. Once again you have educated me!