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Thread: Cracking bodywork

  1. #1

    Cracking bodywork

    I am finding hairline cracks here and there on my f355 replica.

    I am slightly concerned by this, although I expect that cracks are to be expected with the shell being fiberglass.

    Is this a natural occurance? need I worry about it?

    I look at other replicas and while I have noticed other cars with similar cracking, its not something people really talk about so I don't know how worried I should be each time I find a crack and what is 'normal' or excessive...

    Also are these cracks preventable in anyway? I think roads are mostly to blame... holes and bumps are awful these days!

    Any thoughts?

  2. #2

    Re: Cracking bodywork

    Fiberglass will eventually crack. 99% of fiberglass kits out there will have some sort of cracking going on so I wouldnt worry about it too much, keep an eye out though. How old is your kit?

  3. #3
    Senior Member
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    Re: Cracking bodywork

    erick, where are your cracks ?

    im guessing the roof is one , since fibreglass meets metal and the different expansion rates . Thats a tricky one to sort, but if they are other places and you can get behind the panel /corner with the crack you could do a few layups to re-inforce the area then have the paint repaired.


  4. #4

    Re: Cracking bodywork

    cracking most likely has occurred because of road impact stresses
    greater than the elastic limit of the material. if you decide to repair
    you should reinforce the weak area or else the crack will repeat.

    cracks will unlikely occur where steel is bonded to glass. the bond
    will first likely separate before any exterior cracks. road impact transmit significant force to the body. if not reinforced in areas where
    there are spans of body unsupported. the impact load will go the the
    weakest area.

  5. #5
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    Re: Cracking bodywork

    It's because of everything said so far that I treat the buildup a little different than most when I start a project. I do all of my fiberglass work, fill work etc. then get the body in epoxy primer and drive the car. I like to drive it for a minimum of a month and have waited as long as 6 months before moving on to final body work. That is usually enough time for unsupported areas or weak glass work to show up. Another problem that you have with most kits now has to do with time frames. When your order you kit it does not come from stock but is made "fresh" for you once you've put down your deposit. If you are still smelling fiberglass resin when you pick up your kit it is always best to leave it in the sun for a week or two for final "shrinking" of the glass work. If you don't have enough sun consider having a local paint shop put it through a normal bake cycle in a heated booth. If you don't get these fresh bodies to "preshrink" cracking will show up on your first hot day in the sun no matter how good of a job you've done.

  6. #6

    Re: Cracking bodywork

    For my 355, I built a lot of brackets. All body pieces have multiple mounting brackets. For instance, the front fender is bolted (not too tight though) to the stock hood area. I then have two brackets from the front part of the fender where the bumper bolts in to the car. And one more bracket from the lower part of the fender where the rocker panel bolts up to the car. It is amazing how stiff the fiberglass feels with all the brackets.

    The places I worried about are around the rear quarter windows, the door scoop and where the rear clip bolt to the fiero at the rear of the doors. For the quarter window area, we (as in not me) ground down where the two pieces of fiberglass meet and put in a 2" fiberglass matte over the joint. Where ever you have two pieces of fiberglass meet that need to look like one piece, you must grind down the gel coat and fiberglass in some matte at lest 1" over on each side. Other wise, you will get a crack in the future.

  7. #7
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    Re: Cracking bodywork

    Guys, 95% or possibly more is gel coat cracking. This is probably not a structural problem, the laminate is probably not cracked. Of course I have not seen it so I can't say for sure. Gelcoat is far more brittle than the laminate, the thicker the gelcoat the sooner it will begin to crack. A lot of kit car manufacturers have the attitude "they are just going to paint it so I won't buy expensive gelcoat" which adds to the problem. Or if they in a hurry, they will overcatalyze the gelcoat to go faster and that makes it even more brittle. I our shop, if it is fiberglass, the gel coat gets stripped or almost stripped and then it is sprayed with an epoxy primer or a polyester surfacer designed for that purpose. This will minimize and most of the time eliminate cracking. Now if you have a poorly layed-up kit with lots of issues and thin and thick sections, well, you can't turn chicken manure into chicken salad. You can add, mayo, some celery, maybe even a dash of dijon mustard and getting it looking pretty good, but YOU know it is still chicken manure.

  8. #8
    Senior Member Mr355's Avatar
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    Re: Cracking bodywork

    This topic is related to a problem I had with blistering of the paint job when my car was out in the sun. It looked like hundreds of little air bubbles were trapped under the paint. I have done nothing with the car since then due, in part, by this very disappointing discovery. Someone said that it may have been caused by trapped solvent. Can someone explain in better detail what went wrong? And Does the gelcoat have to be removed completely to fix this problem? Thanks, Rob.

  9. #9

    Re: Cracking bodywork

    I'm no expert, but my car was beginning to experience what you are describing before I repainted it. My painter said that it was because the previous owner used cheap, lacquer-based primer (probably the red spray can stuff) under decent white paint. The result was shrinkage/expansion that caused "pimpling" to occur. If you pick at those bubbles of yours, you see air underneath.

    I got my car stripped right down to the gelcoat, reprimed, painted and clear-coated. It cost a lot ($5K CDN), but I've put enough time and effort into it that if my paint crapped out on me after a year, I'd probably go postal on someone or something.

    If you can, strip it down, get it done right.
    Meddle not with the affairs of the Dragon, for you are crunchy... and taste good with ketchup.<br />http://www.rc-sub.com/resources/grap...ni/avatar2.jpg

  10. #10
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    Re: Cracking bodywork

    Yeah, blistering is really nasty, especially after you spent a lot of time and money getting everything to look "just right" and you think you're done. Problem is those blisters can come from so many sources. The gel coat can still be "off gassing" from manufacturing. The painter might have not allowed sufficient "flash time" on his base color coats. The clear coats could have been rushed over the base color. There can be moisture trapped in a high build 2k poly primer (the talc wicks moisture) and on and on...
    As said before stripping it all off and starting over is the only way to start eliminating all of these possible sources. You or your painter have to follow the product sheets like they were a religion to eliminate this from happening again. Watch time windows, temp.s, flash times, etc. to get a worry free job.

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