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Thread: How to fix cracks in fiberglass?? with picture

  1. #1

    Default How to fix cracks in fiberglass?? with picture

    Hey all, working on a new fiberglass hood and have a corner that has some kind of cracks :mad: . I noticed them after sanding the entire hood and wiping it down with wax and grease remover. Also, the "cracks" bleed if I wiggle the corner some. What is the best way to fix this?

  2. #2
    Join Date
    Jan 2006
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    248

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    must be a cincinnati composite hood they are a body mans worst nightmare just fiberglass it tons of different prodcuts you can you but i can tell you now it sounds like a low quality hood and after you get it ready and paint it wont be long before it starts to spider crack everywhere

  3. #3
    Join Date
    Nov 2005
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    East Tennessee
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    Just simply take a die grinder with a small bit and v the split out until it ends.If it ends toward the middle of the hood,drill a small hole at the end of the split.Take some short strand fiberglass (evercoat is what i use) and spread it in,da the fiberglass off with 80,then spread a smooth coat of body filler then block sand it to your choice of grits.

  4. #4
    Join Date
    Nov 2005
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    lower Michigan
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    I agree with Chris. One way or the other you have to sand/grind to the base of the crack in the fiberglass. If there are too many spider cracks to "V" out each crack then it might be easier to use a sanded like a mud hog to remove the gel coat in the affected areas right down to fiberglass matt. The odds are about 99 - 1 that the spider cracking in your hood is just in the gel coat and not in the fiberglass matt.

    If you just spray any kind of primer or bondo type materials directly over the cracks they will most definately re-appear again shortly. Thats why the cracks have to be sanded or ground down to the base of the crack.

  5. #5
    Join Date
    Dec 2005
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    IN
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    Default Cracks

    If you want the repair to last, you should grind the gel coat off and put a few more layers of fiberglass mat over it, sand that down then finish off with bondo.There is no way to tell if the cracks are in the gel or all the way down into the glass without removing the gel first.Once you remove the gel blow it off good and clean it, you will be able to see all the stress cracks in the glass. Being a hood , A hood is going to vibrate and get slammed alot and this will cause the cracks to spread if they are not fixed correctly.

  6. #6

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    Thanks for the suggestions!... I will try grinding out the cracks. The rest of the hood seems to be fine, just this corner where the box was dropped by good ol' UPS.

  7. #7
    Join Date
    Nov 2005
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    Pensacola FL
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    Quote Originally Posted by Phil V
    The odds are about 99 - 1 that the spider cracking in your hood is just in the gel coat and not in the fiberglass matt.
    Of the thousands of stress cracks that I've repaired on boats, I've never seen a stress crack that was only in the gel-coat and not in the fiberglass underneath it.

    I also wouldn't reccommend that you "V" out the cracks, those types of repairs just aren't strong enough to hold up and almost always come back later on. I've also never drilled a hole in the glass where a stress crack ends and Im not sure why you would want to either.

    When I repair a crack like that, I grind down about 1/8 inch into the glass for about one inch on each side of the crack (2 inches wide total) and lay one piece of fiberglass cloth over it. After it sets up, lightly grind it and apply filler. Just be sure that you grind deep enough into the glass to make room for the layer of cloth you're going to put on top of it.

  8. #8

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    How can I tell if there are any more of these? I don't want them causing me problems later. Also would Evercoat "Tiger Hair" long strand reinforced fiberglass filler work as a patch after sanding down to fiberglass?
    Thanks Again

  9. #9

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    It should work, at least for a while, but having experience with boat repairs/fiberglass and seeing the location of your problem, the only thing that will last is what Jon E suggested. You need to grind out the area with the cracks, build it up with fiberglass mat and resin then sand it down and apply filler. When I first started with fiberglass repairs on boats I tried the v notch on the stress cracks followed by filler but it just didn't last. The crack would reappear within a few months.

  10. #10
    Join Date
    Mar 2006
    Location
    Columbus, Ohio
    Posts
    118

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    Ford,

    Don't use fiberglass cloth to fix the cracks, thats for boats and will show thru after its painted. Trust me, I've had a Corvette shop for 29 years. The easiest way to find thes stress cracks is to wipe the surface with a fast enamel reducer. Do small 1 square foot areas at a time. Look closely when you first wipe the reducer on. You will see small "dry" spots as the reducer goes down into the cracks. Mark these with a pencil so you can find them later. Also look carefully as the reducer dries. It will dry last in the cracks making them visible. Mark these also. Next take a 24 grit grinding disk and carefully grind down all the gel coat in the areas that you marked. Now retest this area again with the reducer. If you don't see any tell tale signs of the cracks, just feather these areas and fill with some Fiberglass Evercoat 994 SMC bonding adhesive and finish off with bondo etc. If on the other hand, you still see cracks after removing the gel coat, then you have fiberglass damage. Grind down this area about 1" in all directions. Grind down about 1/8" deep and taper this out. Now use fiberglass MAT to fill this area, usually 2 or 3 layers of ounce and a half mat will be sufficient. When cured, grind down and finish with bondo etc.

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