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Thread: fiberglass advice

  1. #1
    Member cormit's Avatar
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    Default fiberglass advice

    Getting ready to bottom paint my 36' Roberts. Decided to pry off one of the outdated and monstrous drag producing transducer fairings. Many chisels and pry bars to overpower the incredibly tough 3M 5200. I eventually won the battle, drilled a new 2-3/8 hole for a tilted element ... flush mount Airmar B-60 transducer. Cleaned up the spot where the old fairing was and noticed that there appears to be no gel coat where the fairing was attached. Maybe it was glassed in at the time the hull was originally built ... anyway, my question is this: Do I have to gel coat this area .. or can I just go over it with bottom paint? I know there are some glass pros out there .. here's a couple of pics.






  2. #2
    Member Anythingalaska's Avatar
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    Well it's all up to you really. You could paint right over it, but that's not the professional way to do it, so I wouldn't do that personally. It's most likely fine just being painted over, but I can't stand the thought of having un-gel coated fiberglass on any of my boats. You've already got the boat out of the water; you might as well do it right. I would put two coats of gel coat on; then sand/abrade it. After the gel coat has cured, give it a quick acetone wipe to clean away any stray oil/dirt and then paint over the gel coat. If you don't abrade the gel coat, the paint will develop spider cracks over the gel coat. Install the new transducer using Sikaflex instead of 5200. It's more flexible, easier to remove than 5200, and all around better in my opinion.

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    Member cormit's Avatar
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    Thanks for the advice Anythingalaska ..... guess I probably already knew that was the right way to do it. I have a full unopened gallon of Fiberlay Gel-Coat .... it's been in the gear locker for a couple of years and most likely been froze a time or two ..... hard to say if it's still any good or not. Maybe i'll test it on some scrap and see if it gets hard.

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    You can Gel-Coat, or Devoe 235 epoxy primer. You should seal the glass. For a small area like you have I would mix it on the hot side. Make sure your gel-coat has sealing agent in it or it will stay tacky.

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    Member Anythingalaska's Avatar
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    If it's still in liquid form and there is no lumpiness or coagulation in the gel coat; it's probably okay. Also; does the gel coat contain wax? Wax is essentially the surface seal of gel coat and is what gives it it's waterproof/weather barrier. Also, it doesn't really matter that it's such a small area to patch, no need to mix it overly hot unless it's cold enough out to warranty it. Mix up your gel coat and resin, and spread it on as thick as you can without it running\, the first coat will always seem somewhat thin. If you're worried about cure time or cold; just put a heat lamp on it a couple feet away.

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    Member cormit's Avatar
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    I also have a small amount of system three epoxy resin ...... is that an acceptable top coat sealer when applied over polyester resin? Might be easier to mix for a small patch. Thanks everyone for the tips ..... aluminum is more my area .... not all that sure about the fiberglass techniques.

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    Member Anythingalaska's Avatar
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    I would stick to gel coat.

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    Member Akgramps's Avatar
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    Unlike epoxy polyester resin does have a shelf life, can be 6 months, but do a test if it goes off it should be ok.
    And you should be able to scuff and apply gelcoat over that area, it can be hard to get it on thick enough w/o spraying, and if its not thick enough when you sand you will go through the gel and have to start over. The last coat will need wax or cover with PVA top seal as polyester will not completely cure when exposed to the air. It will seem hard until you go to sand it and then it will gum up your sandpaper.

    It should be sealed as fiberglass can be porous, I suppose it is the fibers them selves that can wick if not fully saturated with resin.....but that is just a guess.

    You should be careful if using acetone, make sure it flashes off, which it does rather quickly, but for the sma ereason you are sealing the fiberglass it cab absorn the acetone into the fibers and potentially cause some grief. Although I have done it .....and if you wait it should be fine. But there is a point to be made about absorption and wicking. Just use air to clean the area after you have sanded to expose fresh material.

    Gelcoat can be a PITA......you can apply several coats with a roller, it will take a lot more than you might think....at least it always seems that way to me.

    You can use epoxy, there can be what is referred to as "Amine blush" with epoxy and some say epoxy over poly is ok, but not the other way around....so as long as the bottom paint you are using can be applied over epoxy and most can, epoxy would be easier to use than gelcoat.....hope this helps....I am not a glass man either....but necessity is the MOTHER..... that gets it done....
    “Nothing worth doing is easy”
    TR

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