Products needed to cut, shorten, & splice a bumper cover

Schroeder

Schroeder

Promoted Users
I picked up stinger fiberglass front and rear bumper covers for weight savings on my '77 trans am. The rear cover fits pretty bad. The angle on the outside where the cover merges with the bottom of the quarter panels is wrong. The bumper cover is too wide by almost an inch at various places on the outside edge.

I am hoping I can get away with cutting a little splice on the bottom web where the side " wings" of the cover go out to meet the quarter panels, but I think I'm going to have to cut and splice this thing in 2 places. I'll have to cut somewhere in the middle of the straight section under the tail lights on the right side, and do the same thing on the left side. Cut, take the appropriate amount out to get a good fit on the outside, and re-splice together with fiberglass.

Is it possible to do this and still end up with a strong bumper cover? In a thread on another forum someone mentioned that they used a company called US composites. The website looks pretty basic. I was wondering if I just need to call them, describe my situation, and see what sort of bill of materials they can put together for me.

I probably also need to build up and reshape the radius where the bumper cover comes into meet the quarter panel under its tail extensions where houses the tail lights. Do I just build this up with multiple layers of fiberglass? Is there any way to do this sort of thing with the endura bumper? It fits a little better. The radii on it would still need built up, but I just asked somebody this week and another thread about how they did something similar on a nose piece on a GTO. They use some 3M plastic product. I have it listed in my private messages.

I have looked for YouTube tutorials on this. There are lots of videos every repairing fiberglass bumpers but it is usually on something that still maintains some form of attachment to the rest of the bumper. For example, it's like somebody hits a parking block and a section of the lower bumper is hanging off. They grind a v into the crack interface, and fill it with product to form it back to the large section of the bumper. I'm not sure that's entirely applicable here. I want to cut this thing All the way through in two places. It's probably less than a quarter inch thick.


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fiberglass parts are just a basic starting point. they almost always need to be cut apart and glassed back in to make them fit right. some are better than others though. us composites is a big industrial supplier. they really arent going to educate you on what you need. you need to call them and already know what your looking for. if glass is done correctly you can certainly cut that bumper apart and reglass it and have it be stronger than it was before. the only thing you should need is some chopped mat, a gal of general purpose polyester resin, some body filler and primer. with those you can make the bumper into whatever you want.
 
Jim C said:
fiberglass parts are just a basic starting point. they almost always need to be cut apart and glassed back in to make them fit right. some are better than others though. us composites is a big industrial supplier. they really arent going to educate you on what you need. you need to call them and already know what your looking for. if glass is done correctly you can certainly cut that bumper apart and reglass it and have it be stronger than it was before. the only thing you should need is some chopped mat, a gal of general purpose polyester resin, some body filler and primer. with those you can make the bumper into whatever you want.
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Thanks for the reply. Do you have a recommended supplier or product line? Anything I should stay away from? Is US composites a good source?

Evercoat rage ultra does list fiberglass as a suitable substrate, but is there something else I should use for the best longevity? Fiberglass flexes more than metal. Will the ultra hold up the best?
 
not all but most fiberglass is polyester. bodyfillers are also polyester so yes the two work great together. as usual, keep bodyfiller thin as possible. you should get everything built up with actual glass then grinded, sanded and blocked then the filler is just there to fill pinholes and smooth things out. us composites is a fine source.
 
Check the overall contour of the bumper. A lot of times these parts are popped out of the mold way too soon and then not supported properly. My guess is that the bumper may have lost some of its curve, especially at the corners, and has been flattened out. You might be able to take some tie down straps and pull the ends together a little, and sit it in the sun for a week or so. You can support it on wood blocks on the ends, inside facing up, and this along with the straps might encourage the bumper to go back into a more correct shape. It's hard to say without being there to look at it, but we've done corrections on 'glass parts before. It's really easy if they are still "green."
 
Nearly every fiberglass aftermarket part like that I've ever fooled with has fit like that. I still have nightmares of a Honda Civic body kit I installed years ago. Nearly quit my job because of it. Good thing is, it's fiberglass so you can modify it to fit. Be prepared for it to be a ton of work though. Do as Jim C says and build it up with actual glass and resin. Don't be tempted to cheat by using fiberglass filler.
 
I used epoxy resin and cloth to reattach a bumper that I split in half.
Polyester resin is a good option too, but the epoxy resin is very strong.
I used total boat' epoxy resin because these bumpers will see lots of vibration.
 
crashtech said:
Check the overall contour of the bumper. A lot of times these parts are popped out of the mold way too soon and then not supported properly. My guess is that the bumper may have lost some of its curve, especially at the corners, and has been flattened out. You might be able to take some tie down straps and pull the ends together a little, and sit it in the sun for a week or so. You can support it on wood blocks on the ends, inside facing up, and this along with the straps might encourage the bumper to go back into a more correct shape. It's hard to say without being there to look at it, but we've done corrections on 'glass parts before. It's really easy if they are still "green."
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Thanks for the reply. This has been sitting in a box for a couple years. I doubt it's green, but it's in the mid '80s around here right now. I can try doing as you said. I don't think it can hurt.

Chris_Hamilton said:
Nearly every fiberglass aftermarket part like that I've ever fooled with has fit like that. I still have nightmares of a Honda Civic body kit I installed years ago. Nearly quit my job because of it. Good thing is, it's fiberglass so you can modify it to fit. Be prepared for it to be a ton of work though. Do as Jim C says and build it up with actual glass and resin. Don't be tempted to cheat by using fiberglass filler.
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I was not planning on cheating at all. From some YouTube videos I have watched I am thinking I need to cut this as I described and showed in the pictures. Next I angle a large, long sloping v back away from the cut. Next I take a long 2x4 and clamp it to the bumper way away from the cup. This will keep it flush and planer and hold the multiple pieces together. Next I bridge the gap with fiberglass and resin. I build this up for several layers. I don't know how many times I have to do this. I guess I just look and kind of see what I think is enough? After all this dries undo the clamps and repeat this process on the back side with the clamp on the outside of the bumper cover. Then I sand it down and sand off all the matting I just put on. A fairly small area should be left that just spans past the groove I sand it in where the splice occurred. Is this more or less right? Is this what you consider the "right" way?

ahhgaragetime said:
I used epoxy resin and cloth to reattach a bumper that I split in half.
Polyester resin is a good option too, but the epoxy resin is very strong.
I used total boat' epoxy resin because these bumpers will see lots of vibration.
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Thanks a lot for the reply. And do you have specific products and part numbers that you care to share? I know as soon as I just go and buy something under the general terms that people speak about here I will post the name and somebody will say,"that stuff sucks! I had X and Y experience with it!" haha. I'd like to get it right the first time.
 
Most likely your parts were made with polyester resin. Buy it from a place that specializes in fiberglass supplies, like boat repair supply for example. What you want is laminating resin, it has no wax in it like the big box store DIY resin. The glass random strand mat has something in it to bind it together that the polyester resin dissolves but is not compatible with epoxy resin. So if you want to use epoxy resin make sure the glass mat is compatible.
The way I would make splices is to grind a decent taper on both sides of the cut (inside or outside surface) about half the thickness. Precut strips of mat that go from narrow and progressively wider. Mix resin and stack them in the bevel wetting the mat out. When that cures grind a taper on the other side right to new laminate along the cut and repeat the process.
 
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metalman said:
Most likely your parts were made with polyester resin. Buy it from a place that specializes in fiberglass supplies, like boat repair supply for example. What you want is laminating resin, it has no wax in it like the big box store DIY resin. The glass random strand mat has something in it to bind it together that the polyester resin dissolves but is not compatible with epoxy resin. So if you want to use epoxy resin make sure the glass mat is compatible.
The way I would make splices is to grind a decent taper on both sides of the cut (inside or outside surface) about half the thickness. Precut strips of mat that go from narrow and progressively wider. Mix resin and stack them in the bevel wetting the mat out. When that cures grind a taper on the other side right to new laminate along the cut and repeat the process.
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I'm looking at the medium epoxy resin EPOX-635313 here. This is their "thin" epoxy system. I'm looking at the 6oz e mat FG-C0638 here.

I figure I'll get some rollers, brushes, and shearers. Is this a good selection of products?do I need any anti-bubble stuff or side products? I saw a 3M anti-bubble product on the US Composites site.
 
You dont want to use woven mat like that. You need chopped stranded mat. If you ise woven then your pai tjob will look like a screen door when you pull it out in the sun. The read through will be terrible. While i am a big advocate for epoxy, in your situation its going to be a waste of money and slow you down. The whole bumper will be made of polyester so you will gain nothing from the epoxy. Epoxy is much slower to kick off than poly and poly is a little easier to work with.
 
Jim C said:
You dont want to use woven mat like that. You need chopped stranded mat. If you ise woven then your pai tjob will look like a screen door when you pull it out in the sun. The read through will be terrible. While i am a big advocate for epoxy, in your situation its going to be a waste of money and slow you down. The whole bumper will be made of polyester so you will gain nothing from the epoxy. Epoxy is much slower to kick off than poly and poly is a little easier to work with.
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Here's some 1.5oz chopped mat. Here is a SM-435025 polyester resin I'm considering. It's general purpose. This is actually the 2nd choice. Their high strength version has a long lead time due to the scamdemic. My first choice is one of their 700 series resins SM-700025 in a quart. Is this a must or a lot better option if available? It can be found at the same link and page.
 
Yep ounce and a half mat and regular general purpose resin is all you need. No need to get any special. They would have ised the cheapest materials available to make the bumper so its a waste to go beyond that. If this was a really high end part that you spent a couple grand on then my recommendations would be totally different but i have dealt with parts made to the level of what you have there.
 
Whether epoxy or polyester resin, make sure it's fresh enough. Epoxy is stronger & shrinks less but it's messier & more expensive. Can epoxy over poly, but not other way around. For new stuff I'd personally use poly resin. Save the expensivd high tech stuff for repairs on aged product. Be sure to have enough matt per resin in the mixture, as resin alone is weak & more crack prone. Chop up some matt into strands for packing a little extra into low spots. Be careful about working out air pockets.
Boat stores that regularly turn over material can have decent general resin, homestores & local body shop supply stores usually have old stuff.

Basic fiberglass methods with basic materials haven't changed much in forever. A 50 yr old boat repair manual can have good basic info. Different ways of attacking things. For the front side of things, always good to bevel back material around cuts or breaks, tears , etc. You could duct or aluminum tape together front side & put a layer over backside to hold together initially, then fully bevel front side & build up to flush enough for body filler after sanding. Evercoat g-2 or similar is also great for fine tuning & blocking everything. Can use regular filler on top of & more g-2 again if needed to not abuse thickness of g-2.

With ANY fiberglass work, including condition of new products, Fiberglass always shrinks & cures to the hottest temperature exposed to. So setting supported or installed parts in sun & or artificial heat/ uv lights in cycles will help to stabilize parts before final blocking. Otherwise your hard work will go to crap in fitment & ghosting lines.

Stinger's stuff is pretty fair quality compared to some, believe it or not.
 
jlcustomz said:
Whether epoxy or polyester resin, make sure it's fresh enough. Epoxy is stronger & shrinks less but it's messier & more expensive. Can epoxy over poly, but not other way around. For new stuff I'd personally use poly resin. Save the expensivd high tech stuff for repairs on aged product. Be sure to have enough matt per resin in the mixture, as resin alone is weak & more crack prone. Chop up some matt into strands for packing a little extra into low spots. Be careful about working out air pockets.
Boat stores that regularly turn over material can have decent general resin, homestores & local body shop supply stores usually have old stuff.

Basic fiberglass methods with basic materials haven't changed much in forever. A 50 yr old boat repair manual can have good basic info. Different ways of attacking things. For the front side of things, always good to bevel back material around cuts or breaks, tears , etc. You could duct or aluminum tape together front side & put a layer over backside to hold together initially, then fully bevel front side & build up to flush enough for body filler after sanding. Evercoat g-2 or similar is also great for fine tuning & blocking everything. Can use regular filler on top of & more g-2 again if needed to not abuse thickness of g-2.

With ANY fiberglass work, including condition of new products, Fiberglass always shrinks & cures to the hottest temperature exposed to. So setting supported or installed parts in sun & or artificial heat/ uv lights in cycles will help to stabilize parts before final blocking. Otherwise your hard work will go to crap in fitment & ghosting lines.

Stinger's stuff is pretty fair quality compared to some, believe it or not.
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What's G2? By the way, I am watching a couple YouTube videos on fiberglass repairs. Why need any gel coat products? I already placed my order with US composites, so I will need to know quickly to get it added to the order.
 
G-2 or other sprayable polyester primer surfacers have some of the characteristics of your typical fillers, but give a slightly harder fiberglass type surface. Mixes with the same mekp hardener as fiberglass resin. Makes a great substitute for gelcoat as it is harder & more durable than basic filler, BUT is more prone to cracking if flexed if thickness is abused (too thick), just as with gelcoats. Sprays rough & sands smooth, which acts like it's own guidecoat.
I'd definitely finalize with spi epoxy, which does have strength in thickness & sands well.
 
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