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Dear All - has anybody succesfully removed its luggage rack from their car (I have a C3, but I guess it applies to all corvettes), filled the holes and repainted the car without ending up with shrink cracks etc soon after that. I assume it should be possible but it likely requires a more drastic approach; anybody tips (do's and don't s)?
Eric
It can be done but it takes some time. This is the method I use. First you grind back the holes at a taper and make the patch 2-3 inches on each hole. I use glass mat that I tear up so all you have is loose strands. I put down a layer of resin then a layer of mat and build it up and finish by rolling the patch while the glass is still liquid. With this base and good finishing and blocking I have had great results. Glass the holes shut when you first start the project as the longer they dry the better. This was the method taught by an Ecklers worker at a school.
Thanks Joe - I have used the 'search' button, and no results, but for some reason if you use the 'archives' section you will be successful. Thanks again!
What I am trying to say, although badly, is that every repair of this nature that I have seen done (about four cars total, using various methods of repair) eventually became detectible. In other words, I have seen, after a period of time, that the repair was made. Usually takes years, unless someone just fills the holes with bondo, then it takes weeks.
I wonder if it has anything to do with resonance / vibration of a large flat piece of fiberglass.
The one that I saw repaired that never did show through (as far as I know) involved replacing the entire deck panel with an NOS panel.
If were to attempt this, I'd find a chunk of OEM rear deck fiberglass and cut 3" diameter patches from areas with the same contour as the areas needing filled.
I would then enlarge the bolt holes in the deck to approximately 1.5 inches and then step grind half way through the deck skin out to the 3 inch diameter to match the patch.
Next I would step grind half way through the patch down to the 1.5 inch diameter.
The end result would allow the patch to nest into the repair area with approximately 3/4 overlap around the patch area. With all the fitting work complete, the patch would be flush on both the inside and outside surfaces of the repair area.
I would then remove the patch and clean both surfaces of the overlap area. When completely dry, I'd mix up some high strength epoxy paste, smear it onto overlap area of both the rear deck and the patch and then push the patch back into place.
I would then cover the repair area with wax paper and put a sandbag over the patch to maintain some contact pressure overnight.
Let the repair cure for a week and then block sand and finish with a good fast build primer surfacer and paint.
I had a similar project but it was with the antenna hole. I ground the underside and took a piece of an old panel and used REN to hold it in place.I then ground out the hole and laid mate and resin using a roller.I am not sure if this is applicable to your problem but it is probably one of the best ways to fix a hole..
Hmmm...Let's see if I have this right; You have a 1/2" diameter hole you want to fill, so you would start by making the 1/2" hole into 1.5" hole before you start? Seems like the wrong direction to me, Tracyman.
Since the ideal repair should have resin and mat laminated first on one side, and then on the other, the 1.5" patch you propose would essentially be ground away to nothing from grinding on both sides, and the 1.5" hole you made would be filled with fresh resin and mat. If I'm adding fresh resin and mat to replace missing fiberglass, my preference would be to keep that new fiberglass to a minimum; i.e. a 1/2" hole plus what's necessary to fill the gound tapers.
Actually, Lyle's first description sounds closest to what I have heard and used most often. They tell you to tear the mat like Lyle describes, but besides being somewhat inexact and tedious, I found by the time I tore the mat piece to size, it bore little resemblance to the shape of the ground area I'm trying to fill. I typically build the resin and mat above the contour, and then grind/finish sand back as close as I can to contour. In that case, cutting or tearing the pieces to size has no effect on the final finish.
My description isn't clear enough. There is no added stand fiberglass or resin. The repair is flush on inside and outside surfaces with no added glass or repair material on the bottom side.
The biggest enemy of any repair of this nature will be thermal expansion and contraction. My method uses the same material that the deck is made from and is the same thickness as the deck when completed. There is no added mass with disimilar resin systems or extra back-up structure on the underside.
I've never had to repair a deck but I have repaired fender flares using this method. It require some finesse but like I said, this is how I would do it.
Be sure to grind a tapered area around the hole, starting at about 2"-2.5" radius from the hole center and tapering to almost half the thickness depth at the center. Use about a 36 grit disc for the grinding, and cut (or tear) your mat pieces to cover the ground area.
They say to use 3 layers top surface, and 3 layers bottom surface, but I like to use at least four, and cut the diameters of the mat pieces progressively smaller to reduce the build up at the edges. Mask everything except the ground area leaving a 1" or 2" margin around the outside of the ground area. As you roll the laminated resin and mat, the sticky area is going to grow. If you get resin on top of the masking tape, it's OK, but you'll probably have to grind/sand the resin off to remove the tape...leaving the tape in the repair is not an option.
Final contour is probably best done with body filler; you can grind/sand the fiberglass to contour if you're careful (no filler), but it's tedious work...if one stroke takes too much, then you have to fill anyway.
I would not use any backing strips or other additional thickness material, or leave the cured mat rough and ready in this repair.
The reason you grind the taper into the edge of the repair is too increae the bonding strength of the new fiberglass. You laminate both sides of the panel for the same reason...strength. Once you return the laminated material to contour on BOTH sides, and used the same material (polyester resin and fiberglass mat) as the original panel, you have brought it back as close to a whole, homogenous panel as it's ever going to get.
My objective would be finish the top to contour, and on the underside to flatten any thickness in the lamination area down to near contour...in this relatively hidden area, how close to contour, is left to the individuals discretion. For a judged car, my objective would be to completely hide the repair from the judges, even those that could turn their heads completely around to look up under the deck.
Flares are a little bit different deal. The C3 deck is virtually flat, an literally so over an area 5" in diameter. Restoring the more complicated shape of a wheel opening forces you to replace the flare with donor piece...lamination techniques should remain the same.
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