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Stepside beds and dually fender repair. SMC not fiberglass..

Discussion in 'Paint / Body / Detailing' started by 98nightmare, Aug 22, 2013.

  1. 98nightmare

    98nightmare Bill

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    Most people use fiberglass to shave the steps, gas door and even tail lights.. even bonding roll pans. This info will tell you why it always cracks.. Do NOT use fiberglass on ANY late 70s and up Chevy panels that look like fiberglass. They are actually made from a product called SMC. Hopefully this will explain the great myths of how to fix or customize stepside beds and or dually fenders...






    A new composite material is gaining widespread use in the automotive, industrial, and personal watercraft markets that presents unique repair problems. It is called SMC, or Sheet Molded Compound. Recognizing SMC from other types of FRP composites is critical so the proper repair can be performed. Parts made with SMC are produced in compression molds, so they are smooth on both the inside and outside. That is the first clue to look for when identifying them. Next, SMC parts do not have an outer gel coat, but they are usually painted or color molded. When the paint is sanded off, the underlying surface has a marble appearance. Finally, when damaged SMC is sanded, short coarse fibers are exposed and a dryer powdery dust is produced compared to conventional materials. These hints will make SMC identification quite straightforward. SMC is a polyester-based material, but it cannot be repaired with polyester resin. This is due to the mold release agent that is present throughout the entire SMC part. Unlike conventionally molded parts where release agents are applied to the mold surface, SMC is compounded with them in the resin mix for quicker processing. This means that as the damage is sanded to prepare a good bonding surface, fresh mold release agent is exposed. Polyester resin products are not strong enough to adhere to this surface. SMC SHOULD ONLY BE REPAIRED USING EPOXY-BASED RESINS, FILLERS AND ADHESIVES. When painting, use only catalyzed type paint systems. Once the extent of the damage and the type of material used is known, determine if the part should be repaired or replaced. If the manufacturer's specifications are available, check whether the damaged area is too large to be repaired. If no information can be reviewed, make a quick estimate of the materials and labor time needed for the repair and compare the figure to the price of a new part. A savings of at least 50 percent is the typical cut-off point to warrant proceeding with the repair.

    *** Most affordable product with the longest working time is a product called Marine Tex... It can be found on Ebay

    This is a link to a proper video of a repair, they use a two part epoxy that is the dual tube with mixing tip. http://m.youtube.com/watch?v=eGaF15W3mXA&desktop_uri=/watch?v=eGaF15W3mXA
     
    Last edited: Aug 22, 2013
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  2. DRAGGIN95

    DRAGGIN95 Warranty Killer! Staff Member

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    It is stuck. Great info!
     
  3. 98nightmare

    98nightmare Bill

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    Thanks bro!
     
  4. SCOTTYINWV

    SCOTTYINWV si vis pacem, para bellum

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    :handshake: thanks a million and sweet truck man!
     
  5. 88GMCtruck

    88GMCtruck I'm all 8-Luggy!

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    Great info.

    The stepside fenders on my 88 are de-laminating and cracking. I was lucky enough to pick up a pair of damn near perfect bedsides to replace them instead of repairing them.

    The driver's dually fender on my 98 has 2 cracks that I will likey repair unless i trip over a new fender somewhere.
     
  6. 98nightmare

    98nightmare Bill

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    Thanks guys! Wish id found this out a few years ago...lol
     
  7. michael hurd

    michael hurd Stalker be gone.

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    You can use epoxy to repair fiberglass, but not the other way around, and part of the reason is that polyester resin as it cures, it will shrink 3%. This action will weaken the bond, even if prepped with a coarse grit disc. Fusor T-21 is your friend when it comes to SMC repairs, and it works great on fiberglass as well, but it is pricey.
     
  8. dagen_1

    dagen_1 OBS 4 Me

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    thanks for sharing bill... i don't own a step-side bed (yet) but might end up with one some day. good to know!
     
  9. 94Sierra4x4

    94Sierra4x4 All out OBS.

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    And if anyone is curious - that Marine Tex is fvcking tough .. I had a little crack in the hull of an 18' boat I had a couple years back.. Bilge pump was always having a working out.
    Hit the crack with Marine Tex - let er set - smoothed it out a bit - and never turned the bilge pump on again.
     
  10. BHBurban

    BHBurban GMT 1600

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    Good info to have posted.

    I lost count how many times I've told people that stepside bedsides were SMC, not fiberglass...


    If you trip over it, you'll crack it! :lol:


    Funny how he's repairing 400 dually fenders in the how to!
     
    Last edited: Aug 26, 2013

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