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  • mike

    Nov. 13, 2011 11:13 a.m. mike Reader

    The hardtop on my '94 Miata has had a crack in it at the top rear corner of the passenger side window for years now. It never leaks water in the car, so I've taken the lazy road and let it be until now. It's about six inches long, so I figure I'd better repair it before it goes any further.

    Does anyone here know if the fiberglass for the hardtop was laid in with polyester or epoxy resin? I'd like to do the repairs with a compatible resin and it would be a great head start to know the original chemistry.

  • Woody

    Nov. 13, 2011 11:21 a.m. Woody SuperDork

    I had a SnugTop with a cracked rear window. It was a track car and I suspect that it was my own fault. I removed the Frankenstein bolts and replaced them with regular bolts. The rest of the top was secured with bolt-on barckets. I discovered that the rear brackets are mainly a locating device and not for securing the top. I went too tight.

    I fixed mine with a GRM decal.

  • MG_Bryan

    Nov. 13, 2011 11:39 a.m. MG_Bryan Reader

    The OEM top is made out of SMC (sheet molded composite) and actually has realease agent mixed into it. I would use epoxy, but I'm not sure what they used to start with.

    Here's and example of SMC http://www.idicomposites.com/en/products/sheet-molding-compounds. I imagine there are a lot of variations between manufacturers though

  • mike

    Nov. 13, 2011 11:47 a.m. mike Reader

    OK, employing a bit of Googleage, I have found a couple of links.

    GRM how to identify an OEM hardtop

    and

    The Miata HArdtop FAQ

    These are great references! I took a critical look at my hardtop and decided that it is an early OEM hardtop with no rear defroster, but with the OEM-style front latches, and alse with the little L-brackets at the bottom of the rear of the hardtop. I couldn't find the word "Snugtop" looking around the rear glass at the driver's side, either.

    As such, the top is made of SMC, sheet molding compound (MG Bryan wins a gold star). Thermosetting resin over chopped fiberglass. This explains why I am seeing what looks like chopper-gun glass fibers in the damaged area, but there's a smooth surface on both the inside and the outside.

    And, according to several sources (including Wikipedia), the resin is, you guessed it, polyester.

  • MG_Bryan

    Nov. 13, 2011 12:00 p.m. MG_Bryan Reader

    http://solutions.3m.com/wps/portal/3M/en_US/Marine/Home/Products/Catalog/?PC_7_RJH...

    Might try something like that since it's designed to stick to SMC

  • mike

    Nov. 13, 2011 12:14 p.m. mike Reader

    This seems to be popular with a lot of folks:

    Evercoat SMC repair

  • motomoron

    Nov. 14, 2011 6:34 a.m. motomoron HalfDork

    I've done a LOT of composite work for decades. Recently I finally got around to repairing a beater Miata top that had a lot of rashed-up and missing bits around the rear bottom edge, and I was mystified that the patches I'd laid up w/ fresh vinylester resin simply peeled off the freshly ground surfaces.

    Thanks MG_Bryan and mike!

    I just ordered a quart of the Evercoat SMC resin and can start this whole ordeal anew. Maybe I can have a hard top on before it's completely ball-numbingly cold out!

  • mike

    Nov. 14, 2011 8:01 a.m. mike Reader

    In reply to motomoron: Be sure to post up your results! Where did you buy the Evercoat?

 
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