Corvette bumper ghost line

5

540goat

I molded in the front and rear bumpers on my 80 vette. I used the flex fiberglass bumpers on the car. I added fiberglass to the inside of the bumper to make them more rigid. I bolted and bonded on the bumpers. Then I ground a V into the seam and laid my fiberglass mat and resin in there. I used the proper resin for this body. I used Evercoat resin for SMC panels. After I sanded the cured fiberglass I filled the indents and pinholes with filler. I then primed block sanded straight and then epoxy coated the whole car and then the next day wetsanded with 400 and put on my base. PPG black. I then put on my universal clear. With the paint not cut and buffed you don´t see anything, the areas look perfect. But after I buffed out the rear bumper area I could see a seam line. You can only see it from different angles and not straight on. The panels are perfect with no ripples in the body work. It also seems to stand out more after I run the buffer over it.
The front bumper which I did the same way is fine as are the top of the rear bumper. I would post a picture but it didn´t show up in it. If you looked at the car you probably wouldn´t notice it unless I pointed it out to you.
 
glass just like steel expands and contracts with heat. buffing equals heat . a whole lot of uv rays will eventually reduce it. did you use epoxy resin ?
 
shine;28257 said:
glass just like steel expands and contracts with heat. buffing equals heat . a whole lot of uv rays will eventually reduce it. did you use epoxy resin ?
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I used Evercoat SMC panel resin. It wasn´t epoxy. It what was recommended to me. Normally I would have used regular resin. I have been using regular resin on corvettes for a long time and never had this problem. I don´t understaand why it didn´t show up on the other panels.
 
With any fiberglass car, especially a black car, you MUST heat cure the repair beyond what it will ever see before final painting....I bet you would be fine with reblocking and reshooting this fall after a summer cure...Dave
 
flynams;28271 said:
With any fiberglass car, especially a black car, you MUST heat cure the repair beyond what it will ever see before final painting....I bet you would be fine with reblocking and reshooting this fall after a summer cure...Dave
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Anytime I paint a car for myself I always let it sit for a few months before I paint it. The rear bumper was done a few weeks ago, whereas the rest of the car was done last September.
 
you need to set it in the sun for a while . polyester resin takes a while to stop reacting to heat. setting inside is not good enough
 
shine;28273 said:
you need to set it in the sun for a while . polyester resin takes a while to stop reacting to heat. setting inside is not good enough
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As soon as we get a warm sunny day on Long Island I will get it out there.
 
Aren't those bumpers urethane? I would have thought that an epoxy based semi-rigid adhesive filler something like SEM 39767 would be indicated. I honestly don't think very highly of repairing a flexible material with a rigid one; I've seen multiple failures with this technique.
 
crashtech;28305 said:
Aren't those bumpers urethane? I would have thought that an epoxy based semi-rigid adhesive filler something like SEM 39767 would be indicated. I honestly don't think very highly of repairing a flexible material with a rigid one; I've seen multiple failures with this technique.
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I molded in fiberglass ones. I stated it in the original post.
 
crashtech;28336 said:
Sorry, I saw "flex" but not fiberglass.
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No problem. But I will tell you I will never use the flex bumpers again. They are very thin and if you hit them woth the grinder you will go right thru without a warning. I had to add fiberglass to the inside to stiffen them up a little. They also are very wavy. I wanted the glass bumper because the urthane warps over time. These came pre warped. I had to do alot of work to get them straight.
 
Every fiberglass part I've ever worked on came pre warped, some worse than others, but they all required hours and hours of work. Dissimilar materials will always have different expansion and contraction rates and hard lines in bond/repair areas will also show this more during temperature changes. Chances are you don't see the swelling in the repair areas when the materials are at the same temp as when the repairs were made? Always grind a good taper so your materials feather out well so you see a more gradual difference in expansion and contraction in different temps-hope that makes sense.
 
Bob Hollinshead;28399 said:
Every fiberglass part I've ever worked on came pre warped, some worse than others, but they all required hours and hours of work. Dissimilar materials will always have different expansion and contraction rates and hard lines in bond/repair areas will also show this more during temperature changes. Chances are you don't see the swelling in the repair areas when the materials are at the same temp as when the repairs were made? Always grind a good taper so your materials feather out well so you see a more gradual difference in expansion and contraction in different temps-hope that makes sense.
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I was just in the garage and you couldn´t see the line. I really don´t think anyone else would notice it. It just annoys me now and will be repaired in the fall. When I did the rear bumper I tapered it about 1 1-2 inches on both side a total of 3 inch taper. I have alway done it like this.

I also did the front bumper the same way, same materials, it just sat longer than the rear before paint. It dosen´t have any ghost line in it at all.
 
WSell today we have our first 90 degree sunny day. Put the vette into the sun to get everything baked good. The funny thing is I don´t have the ghost line or any shrinkage on the top of the rear bumper or the front bumper. I only have it on the sides of the bumper. I did everything the same on both parts.
 
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