Let's suppose that I wanted to create a custom bumper with a somewhat stock appearance, but with unique forms molded in. Let's also suppose that I am too cheap and demanding to simply hand a design to a custom fabricator. If I took my time with cutting up the stock urethane bumper and created my forms with foam and cardboard, could I safely lay fiberglass over the entire bumper? I will prep the bumper of course. I plan to lay the initial outer layer with the bumper on the car, then carefully remove it (for alignment). Then add another layer front, two back, and around all edges. Aside from the fact that my finished bumper will have increased slightly in dimension, is there any reason this will fail? I figure it's like a surfboard. You just glass around a core. The fiberglass is strong in tension, so it only needs to be on the surface. The core does not have to be ridgid, just keep the surface layer from collapsing. Once I have a continuous layer of fiberglass on the bumper, I am free to add more glass or thin layers of fiber-reinforced body filler, correct? Worst case scenario, the fiberglass delaminates from the urethane. The urethane is encapsulated, so it will not form a visible crack or allow water to penetrate, right? Am I crazy?

PS: I already took a jig-saw to my bumper tonight!

Corbin

'95 ESI-T
Now with more power and fewer leaks



Gimme fuel...Gimme fire...Gimme that which I desire

Originally posted by Corbin
Let's suppose that I wanted to create a custom bumper with a somewhat stock appearance, but with unique forms molded in. Let's also suppose that I am too cheap and demanding to simply hand a design to a custom fabricator. If I took my time with cutting up the stock urethane bumper and created my forms with foam and cardboard, could I safely lay fiberglass over the entire bumper? I will prep the bumper of course. I plan to lay the initial outer layer with the bumper on the car, then carefully remove it (for alignment). Then add another layer front, two back, and around all edges. Aside from the fact that my finished bumper will have increased slightly in dimension, is there any reason this will fail? I figure it's like a surfboard. You just glass around a core. The fiberglass is strong in tension, so it only needs to be on the surface. The core does not have to be ridgid, just keep the surface layer from collapsing. Once I have a continuous layer of fiberglass on the bumper, I am free to add more glass or thin layers of fiber-reinforced body filler, correct? Worst case scenario, the fiberglass delaminates from the urethane. The urethane is encapsulated, so it will not form a visible crack or allow water to penetrate, right? Am I crazy? PS: I already took a jig-saw to my bumper tonight! Corbin '95 ESI-T Now with more power and fewer leaks Gimme fuel...Gimme fire...Gimme that which I desire

-MIKE-

Stroked 2.2L

I agree with eclipse982nrRST to a certian extent..

This is the way I would do it.

Like eclipse982nrRST said, get some PVA and put atleast 3-4 coats on your (clean) bumper. You can actually brush this stuff on. Just to inform you, this stuff is water soluable, so dont get it wet.

Now this is where it gets different.

Get some gelcoat, enough to do atleast 3 coats, I wouldnt do anymore than 4. If your wise, you will get something lite, like white since your bumper is a dark color. Just make sure you get everything nice and covered. You need to wait inbetween coats atleast long enough for the gelcoat to tack up. Then I would atleast let the coats of gelcoat cure for atleast 12hrs depending on the temp its sitting in. The colder of course you want it to cure a lil longer. This stuff cleans up with Acetone.

Then get some chopped mat and put atleast 3-4 coats on top of the gel coat. Just like the gelcoat you want to wait inbetween coats for it to tack. You also want to wait a little longer because resin warms up and actually gets hot, so if you pile a bunch on, it will warp and deform your gelcoat. Also, while your laying the mat, becareful of air bubble, ecspecially the first coat. If you get an airbubble in there, there is a chance it will cause a brittle spot in your gelcoat. Just take your time. Id let that cure as long as you cured the gelcoat. This also cleans up with Acetone.

After thats cured, then peel your bumper out. If you find any imperfections you can wet sand them out with 400 grit and refill with gelcoat and wetsand that smooth 400 grit and finish off with 1000 grit.

After you have your mold the way you want it, go out and buy yourself a can of bees wax. Its in the same kind of can you would find turtle wax. I would wax the mold atleast 5 times. You dont want to do all the coats at once. I would do a coat, then wait an hour. The idea is letting the wax soak into the gelcoat. So the longer you wait between coats, the better.

Now that you have it nice and waxed, go ahead and brush some PVA on the mold. You prolly want atleast 3 coats. After the PVA has dried, it is the same process as making your mold.
1. Gelcoat
2. Fiberglass, how man layers is up to you

Peel it out of your mold and your ready to go. Now to make a modified bumper, you can do it 2 ways.

The way I just described and when you pull the fiberglass bumper you made, you modify that, then do the whole process over again. Then you'll have 2 molds, so you can change design when ever you want.

Or modify your stock bumper first, then make your mold.

Your best bet if your going to use foam, is use the stuff in the cans that you use for insulation or use that fiberglass board that you use for insulating walls. Ive found that the resin and gelcoat will melt your normal styrofoam.

You can use this process to make anything. Of course it might be wise to start with something simple then move up the more advanced you get.

This process also holds true when fabricating anything out of Carbon Fiber. The only process you change, is replacing the fiberglass with CF and using clear gelcoat instead of colored. The best gelcoat I have found to use, is the same that is use for surfboards.

Good luck Corbin, just remember to take your time and think things through.

Only problem with gel coating first, especially over a release agent is it will run VERY easy and not be the same thickness everywhere. I have tried this with making several sub box enclosure molds, just doesnt work as a first mold.

-MIKE-

Stroked 2.2L

Huh, never had that problem....

Corbin, I'm actually doing the same thing, but I bought an extra bumper from a local 2gnter to work on. It's been in the backyard for a while, but now I'm getting back into it. When I'm ready to make the mold, I'm going to mount it on the car too so that the shape stays true.

The key is to find a material that shapes well on top of your bumper. After trying everything from putty to clay and aluminum siding, I finally found an excellent media - it is artisitic wire mesh. You can bend it however you want and it remains in that shape. I'm going to put fiberglass over the old bumper/wire mesh to make the mold.

My issue is this, and Corbin I'd like to hear your feedback on it - how are you making the part of the bumper that raps into the wheel wells? To make a bumper with this back part, I may have to make a 3-piece mold. (unless I make the fiberglass very thin and flexible, he he, so I can actually get it out of a one piece mold)

Question for you other guys - where did you get that gelcoat, PVA, and wax (exact names of the manufacturers and source). I used to surf over at fiberglast.com (Excellent info there) and was contemplating buying their stuff - however there products might be overkill for my one bumper.

I buy all my goods from here....a great company to order from and they ship very fast. I think dj, myself and a few others use them also.
http://www.shopmaninc.com/hybrids.html

http://www.murderpimp.com





2gnt T-shirts&swag
http://www.cafepress.com/mads

-MIKE-

Stroked 2.2L