proper way to prep glass hood & dually fenders

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PostPosted: Thu Jun 26, 2014 8:09 am
have a harwood hood and original gm dually fenders that have been soda blasted already, the hood is down to the white layer (assuming gelcoat), has a few hairline cracks that I plan on v grooving out and filling, just don't know what filler/product to use. I am using ppg epoxy & slicksand for a hb primer to block, epoxy 1st?. The fenders are down to the grayish layer with some glass strands visible, blast guy said looks the same as a vette body glass. need some help, want to do it right the 1st time, thanks

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PostPosted: Thu Jun 26, 2014 11:40 pm
First, welcome to fantastic plastic land.... And don't take this the wrong way.... but, why did you have fiberglas parts soda blasted???
From the paint failures I've seen over the last few years soda gets into all the micro cracks and crevices we have in fiberglas and can be very hard to neutralize once it gets down in those pockets. If every single spec. of that soda isn't out of there, including the acid neutralizer you will have peeling paint down the road.
To get to what you have, that Harwood hood is some pretty crappy just open lay up style glas made in an open mold. Nothing special there, you could use a product like Duraglas filler for any minor cracking. On those dually fenders, if they came from the factory, they could be SMC or Sheet Molded Compound which is made in pressure molds for speed and quality control. SMC has a mold release throughout it that requires SMC compatible repair resins or epoxy resins. I would not take a chance on using regular fiberglas repair products on those without knowing that they were not an SMC product. SMC can usually be identified by a slight chalkiness on the inside of the part and much smaller strands of fiberglas as seen on the underside. And yes, Vette body parts are pretty much SMC (with a few other types of plastic here and there).
So where would I head from here?.... First, I'd call the blaster guy and ask him what he did right after the soda blast? Did he neutralize it? If he didn't my first thought would be a wash of vinegar (white or apple cider style) on everything, then dry in the sun for a day or two moving the parts every few hours. Next I'd probably hit them with Dawn and hot water mix, let them set in the sun again for a few day. And finally I'd hit them by hand with a hair dryer on low heat/ high flow to force out anything that may be stuck down in the glas. I'd probably do my repair work right on the bare glas BEFORE epoxy sealing. My thought there is that the repair materials you'll use here should liquify any remaining soda into the repair resin itself and make it inert. After all the repair was done, then I would epoxy seal and continue on with Slick Sand. Tip on Slick Sand, that stuff can turn solid in your gun within 18 minutes or so in hot weather so don't get stuck with an expensive paperweight. Mix it, and shoot it all fast.
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PostPosted: Fri Jun 27, 2014 2:45 pm
yeah, prob created more work for myself with soda blasting, not too many options around here, but I am thorough with all the cleaning, hear all kinds of horror stories about failed paint jobs, but I've also heard many people that have no problem too. I think its like painting, if you don't spend the time to do the prep right, the final product suffers. prob should have 220 it and epoxy over it, but what if theres lacquer under there, you're screwed too! damed if you do-damed if you don't. it's so easy to screw up something with all the chemistry involved, thanks for the reply. fender are off the old body style 73-87 if it makes a diiference if they're smc or not

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PostPosted: Fri Jun 27, 2014 10:52 pm
Okay, got it. Well, one of the worst reactions you could run into is a release of Co2 (carbon dioxide) bubbles if any remaining soda is down in a crack, pocket, etc., and reacts with the epoxy seal coat. On the fenders that time period is still right for SMC. About 80% of fillers, resins, etc., are now rated for SMC so just buy that stuff. Putting an SMC compatible material on regular fiberglas does no harm but the other way around won't work at all.
Metal, wood, fiberglass, we work it all... www.furniturephysicians.com We can restore the irreplaceable!

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