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Repairing Fiberglass Panels - Glass Act
CHP takes a look at repairing fiberglass body panels
Jan 12, 2006
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Repairing Fiberglass Panels - Glass Act
When Corvette hood meets Buick bumper, the Vette's fiberglass hood is the loser. Luckily, it's cost effective to fix this piece. According to John Morrow of Johns Customz & Performance, we could bond the missing piece back in place--if we had it. Lacking that, this area will be rebuilt with new fiberglass.
While we had the 'glass mat and resin out, we decided to fix this small crack in the Vette's rear fender opening. Our fiberglass expert, Johns' Adrian Herrera, ground away the damaged area before we could even take a picture, exposing clean, solid white fiberglass. This is a must if the new fiberglass is to adhere properly.
The second order of business was to remove the fourth-gen Vette's clamshell hood and flip it over onto a pair of stands. There was a slightly more serious crack on the right fenderwell, one that went all the way through the panel. To make a strong repair, Adrian prepped both the top and underside of this area to receive new fiberglass.
An underside view of the Vette's hood damage reveals that this will be a complex job. Our '84-vintage subject feeds air to the engine through ducts in the hood, and the renegade Buick bumper broke into this area, which part of this ducting will have to be rebuilt. Adrian started by using a die-grinder on the shattered fiberglass in this area.
During the sanding and grinding prep on this hood, large chunks of 'glass came loose. This piece illustrates why so much material must be removed. It's ragged, and it's dirty, a bad combination if new fiberglass is to be applied. Check out the thrashed topside of the hood behind this piece--a lot more original fiberglass would be removed.
If you need any further proof that prep is crucial to a proper fiberglass repair job, look no further. Adrian used a mirror and sandpaper to get inside the Vette hood's air ducting, ensuring that he'd be working with fresh 'glass.
By the time Adrian was done grinding and sanding, the full extent of the damage to this hood was visible, and parts of the inner structure that must be rebuilt are easily seen. Most importantly, note the beveled edge that has been created around the repair area. This adds strength to the repair area by providing more area for the new 'glass to bond with the old.
Adrian fitted a piece of sheetmetal around the area to be repaired, the screwed it to the hood.
Once the screw lengths are ground off, this metal will provide a mold for the new fiberglass to come.
With the prepwork done, it was time to get down to laying some new 'glass. Johns Customz uses marine-quality fiberglass mat for greater durability against the elements. The fiberglass resin and its hardener should be mixed according to the manufacturer's specs. Mar-Glass is a body filler that contains strands of fiberglass--it actually bonds with fiberglass mat. The bottle in the middle contains a body glaze, a light filler that will be used to smooth out the repair areas.
After tearing the fiberglass mat to the desired size, Adrian used a paintbrush to soak each piece with resin before applying. This stuff is like a sponge, so plenty of resin should be applied during application.
Adrian worked quickly, sliding the soaked pieces of fiberglass mat under the hood's metal ducting and into the repair area outlined by the metal mold. Note the brush, which helps position the mat and keep it wet with resin. Adrian built this area up until the proper thickness was achieved, which took 4-6 layers of 'glass mat.
Adrian continued the hood rebuild with layers of fiberglass in the groove area created by the hood's leading edge and the outside of the hood air ducts. Adrian used a small piece of cardboard to fill in the broken area of the hood box-like area at the front of the hood. Again, soaked layers of 'glass mat are set down until the proper thickness is reached.
On the cracked quarter-panel, Adrian simply laid on a few layers of 'glass mat over the area he had ground clean. The ragged edge below the wheel opening was trimmed down with scissors.
The more serious crack on the front wheel opening section of the hood got layers of 'glass on both sides to give this area strength. This area is ready to work--as you might have guessed, small areas harden more quickly than large ones, like the hood.
While waiting for the initial hood repairs to harden, we turned our attention to the fender cracks. Using 200-grit sandpaper on a wheel, Adrian showed his expertise by working the wheelwell radius. It takes a practiced hand and great care to sand down the excess 'glass in this area without cutting into the fender line. Go slow and be careful if you try this yourself.
In this shot, Adrian is showing one of the keys to making a repair area look like it was never repaired. Note how he's holding the sander parallel to the fender lip area, matching the original contour here as well as above it on the sloping fender side.
After further smoothing the repair area with 500-grit sandpaper on a D-A sander, Adrian does a little fine-tuning by hand. So far, so good, and the front wheelwell repair looks just as good.
The hood had time to fully harden while Adrian worked on the fender cracks. Removing the metal mold revealed that we were only half done.
After using the coarse-grit 400 sandpaper and sanding wheel to smooth out any rough edges in the new fiberglass on the underside of the hood, Adrian smoothed in a layer of Mar-Glass.
This fiberglass-impregnated filler material will provide a smoother, sandable surface while also adding extra strength to this area.
With the hood's underside done for the moment, Adrian flipped the lid over and, after resanding the repair area to ensure that he was working with clean 'glass, added another 4-6 layers of fiberglass to the repair area. In addition to making sure the hood is as strong as ever, this will provide material to create the proper hood contour.
Once this new patch had hardened, Adrian again got to work with the heavy sandpaper. Note how he sands from the outer edges in towards the middle of the hood in order to maintain the peak that runs down the middle of this panel. The action is similar on the front edge of the hood.
At this point, the coarse work is done. With this extensive fiberglass work, we've got the strength to make sure this hood is structurally sound, and the original shape is in place, albeit roughly. Adrian continued by applying a mixed layer of Mar-Glass and body glaze.
While the newest layer on the hood hardened, Adrian again turned to the fender repairs. After applying a layer of lightweight body glaze and letting it harden, he used a pen to trace the fenderline.
Using this line as a guide, Adrian sanded the glaze with 400-grit paper until it was smooth. The exact repair area is all but impossible to pick out, which is the way we want it.
Returning to a D-A sander and 400-grit paper, Adrian moved back to the now hardened hood. Again, note how he sands from the outer edge in, maintaining the original point on the hood's nose.
Among the things we learned during this project is that there's no substitute for feel. Here, Adrian is tracing the hood's centerline down into the repair area to make sure that he doesn't sand over this peaked area.
With the Mar-Glass/body glaze concoction sanded smooth, the care that Adrian took to maintain the hood's stock lines becomes more evident. This area was treated to a coat of straight body glaze before another round of sanding.
Entering the home stretch, Adrian masked off the appropriate areas of our newly re-glassed Vette...
...and sprayed on a few coats of high-build primer to fill any minute flaws and prepare the repair areas for paint.
The primer didn't take long to dry during a typically balmy California winter, so Adrian didn't waste any time loading up some 500-grit sandpaper to wet-sand the primer.
Don't be surprised if a lot of primer comes off--it is high-build material, after all. Special attention should be paid to the edges of the primered area; the ridge created by the primer will need to be smoothed out.
This cracked lip is history--the flaw is filled, and with the primer sanded smooth, this panel is ready to paint.
To fully rehab this Vette's busted snout, we ordered a new urethane front bumper cover from Mid America Motorworks. Also note the new driver's side fog light, which also came from Mid America. This is one of those jobs that looks harder than it is--side marker lights need to be transferred to the new piece, as well as the side mounting brackets, which are riveted in place. Check out the accompanying sidebar for more info on this process.
With the new bumper cover in place, Paul and John Morrow set the hood back in place.
As you can see, Adrian's careful work has paid off with a near perfect reproduction of the factory hoodline. We'll need to do a bit of fine-tuning on the bumper cover to complete the fit, but we're lookin' good. Next stop for this Vette: tons of sanding, then the paint booth!
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