I've been putting this off for two and a half years. I have to fix the body on the Viper. It's not a huge task, but a big one. The fiberglass bodywork is cracked in several places, some of them quite severely. An attempt had been made by the previous owner to fix the hood, but(unsurprisingly), the repairs cracked. That's not unexpected, I assumed that I'd have to grind out and redo that work anyway. The body damage is what made this car so cheap(relatively speaking anyway). To pay a shop to do the work would likely be $10K plus. Conveniently, I used to build kit cars for a living, so I know a thing or two about working with fiberglass.
The plan is to get the primary bodywork done this year, then paint it next summer. I have a good reason for this. Bodywork of any type will shrink a bit, fiberglass especially so. By waiting to paint it, the fresh bodywork will have several months to fully cure and shrink as much as it's likely going to. To prepare for bodywork, I haven't waxed the car all year, and I washed it repeatedly with Dawn dish soap. This should have left the surface free of wax buildup that would cause problems down the road. The repair area also gets wiped down with Wax and Grease remover.
I decided to start with the easiest repair since it didn't involve actually taking anything off the car. The passenger side quarter panel had a crack in the forward edge. It doesn't really look like much, just some chipped paint and a hint of a crack:
But, it's more damaged than it appears. Using just a pick and a knife, I broke out all the loose 'glass surrounding the damage. This is just the stuff that was already broken loose from the underlying fiberglass. You can see how much was actually damaged.
Up next is the best(or worst) part, taking a grinder to one of the best sports cars America's ever produced. To repair cracked fiberglass, you MUST grind out the whole crack. You can't just bridge across it with more fiberglass. If you do not completely grind the crack away, it WILL show up again down the road. I used my trusty Harbor Freight 7" grinder with a 24 grit disk. It's an astonishingly good grinder for what it cost, and has served me very well over the years.
You want to grind the crack completely out, and grind back the surrounding area where you'll be laying on new 'glass. With a grinder this big and a disk this aggressive, you've got to be careful not to grind too far.
Then we have to lay in some new fiberglass. Body filler alone, even fiberglass reinforced filler, wouldn't be strong enough and would likely crack again at some point. We also need to re-bond the fibers that have broken loose but aren't broken off, and bondo alone won't do that. Additionally, the Viper's body panels are made from SMC. It's still fiberglass, but a slightly different kind than you're used to. Because of this, you can't use standard fiberglass resin, it won't stick well. According to Evercoat, it's because of the mold release built into the SMC's resin. You either need to use epoxy resin, or an SMC specific polyester resin. I'm using Evercoat's SMC Fibreglass Resin. You also want to use fiberglass mat, not the woven cloth. The reason is that if/when it does shrink, you won't really notice the random pattern of the mat. If you use cloth and it shrinks, the square weave showing through will be very obvious. I put on a few layers of 'glass, adding more to build up the corner that was ground away. The tape comes in handy here, it'll help keep you from getting resin on things you don't want resined.
The repair goes all the way to the unground paint. Normally you wouldn't want to put resin over shiny paint because the resin won't stick well to it, but it doesn't matter in this case because that whole area will be ground back past that point anyway.
Up next, we get to use one of my all time favorite bodyworking products. My most favorite is SEM Color Coat plastic/vinyl/fabric paint. My second most favorite is this stuff, Duratec primer surfacer:
It's made specifically for fiberglass, and is essentially a sprayable catalyzed gelcoat(it also works fantastic on metal too). It's basically fiberglass resin with a lot of solid binders in it, and it catalyses with fiberglass hadener. Unlike most primer surfacers, it has virtually zero shrink. You can basically put it on as thick as you want, and it will work just fine. Duratec even says a build of .040" is acceptable. At $100/gallon, it's comparatively cheap too. Because it's made specifically for fiberglass, it will help seal the fresh 'glass better than most products will. Using my trusty grinder, I ground down the new 'glass until it was below my final surface height, then covered it with Duratec. I didn't spray it on for this part. Because it doesn't shrink, and most of it will get sanded off anyway, I put it on with a brush. Seriously. It works just fine that way and is much easier to deal with(less masking, less cleanup, etc).
One of the reasons I love Duratec is that it sands super easy and doesn't clog the paper. After knocking down the high spots in the Duratec with 80 grit paper, it was on to bondo. Like kleenex and sawzall, bondo, even though a brand name, has become the generic term for body filler. Bondo brand bondo is actually one of the worst fillers on the market. Granted, it's better than it used to be, but it's still not great. It sands like a rock, it absorbs moisture like a sponge, and it cracks easier than most other fillers. For just a few more bucks a gallon, you can get much better products. I'm using Evercoat Rage Gold. It goes on smooth, and it sands like nothing. I roughed it in with 80 grit, then finished with 220. The Rage Gold sands well enough that I didn't need any intermediate grits.
When doing bodywork, you always want to use the longest sanding block possible. Too short of a block can leave waves, and avoid hand sanding at all costs because you'll leave waves and finger grooves. I used primary an 8" sanding block for this small area. If you're new to bodywork, do not use power tools. Making panels flat with a hand block takes skill and practice. Making panels flat with power tools is nearly impossible. It's far too easy to sand too much off with power sanders, and you're likely to get waves and ripples that you won't be able to feel, but will see in the final paint. You can see in the pic that our repair area is spreading too. The repair needs to be feathered out into the non-damaged area to get a perfect blend.
After two coats of bondo, I was satisfied with the repair. Body filler will absorb moisture(which is why you should never wet sand it). It's less of an issue on fiberglass because the underlying panel can't rust, but it's still an issue. Many 2K primer surfacers will absorb moisture too. Since we don't want that happening, and the car won't be painted until next year, we once again turn to our good friend Duratec. It's completely waterproof, and will seal the bodywork. This time though, I did spray it. You'll notice I sprayed out past the repair and over shiny paint. Normally, you wouldn't want to do this, because the primer won't stick well to the shiny paint. But, this isn't a usual case. When I do the final bodywork just before paint, it will be block sanded down closer to the repair area, and the whole panel will be primered. The Duratec now is primarily for protection from the elements. You can see I did much more making this time too. My HVLP guns don't have that much overspray, but it's easier to do a little extra masking than clean off overspray.
Another thing with Duratec, since it's catalyzed like fiberglass resin, you MUST IMMEDIATELY CLEAN YOUR PAINT GUN. When properly mixed, Duratec sets up in 20 minutes or so. Once it's set, it's set. Unlike standard 2K paints and primers, there is nothing that will dissolve it. If it sets in your paint gun, you'll be buying a new paint gun.
With the Duratec set, I could unmask everything. I'm left with a repair that's 95% finished, and completely weatherproof so I can still drive my car. It took me a weekend of not working very hard to do this repair. The hood and left quarter are next, they'll be much more involved...
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