I truly apologize for not getting back something written for you sooner. I'm going to run down a step by step as if I were doing the repair. The thing about fiberglass is that there's a million different ways of doing it and allthough different, most are feasible.
Items needed: I would definately have an inside area to place this project, such as a garage with decent ventilation. 1.) You will need resin and catalyst from your local auto parts store. 2.) Fiberglass material 3.) paint brushes to apply the resin mix 4.) bondo & hardner plus various sandpaper for the finishing work 5.) Masking tape, thin wire, tinfoil, C clamps, angle iron (thin metal strips or short 2x4 peices will be ok also). 6.) Protective eyeware, acetone, rubber gloves and dust masks. Items from number 6 should be near for all fiberglass projects.
Step #1 Place your bumper on a solid work surface in a well ventilated work area. Wash all areas to be fiberglassed with acetone.
Step #2 We'll start with the cracked areas such as
and
These areas can be fixed by lining up the crack as well as you can. Try to make the crack appear as if it weren't there. When the sides are lined up correctly, you can apply masking tape to the "outside" area (the facing side or gel coated smooth side. This will keep the resin from bleeding through the crack and onto the gel coated side. You can also use the metal strips and C clamps to keep the crack as straight as possible. Just remember not to crank down on them or you'll be repairing more cracks! Once the crack is lined up well and covered from the front to keep down the resin bleed, lay out enough fiberglass material to cover at the minimum 3 inches all around the crack. Do not cut the fiberglass material either! Don't make it a perfect square! Pull it apart so that there's a ragged edge of fiberglass strands. This will ensure better sealing of the fiberglass. Rip enough fiberglass to make 3 layers over the crack. Mix only enough resin and catalyst to do the job at hand. Follow all of the instructions as to the proper proportions of catalyst for the type of resin that you're using! Use the paintbrush to soak the resin into the first layer of glass over the crack. Continue laying down the next layer and "paint" over it with resin. Finish with the final layer of fiberglass. Do not over use the resin! You only need enough to make the fiberglass material wet, you do not want it dripping. Too much resin will cause a brittle end project. Allow this to completely dry before moving on to the next crack!!!
Step #3 Repeat the same steps as #2 for the next crack as pictured above. Allow it to dry before moving on also, I would suggest repairing one crack a day to allow the fiberglass to fully cure.
Step #4 Fixing the large "open areas will be a much tougher job. If you have the missing pieces, it will make the job much easier! WE will start repairing these now
If you do have the missing pieces, simply insert them into the opening, tape them in and proceed repairing them much like the above cracks.
I'm assuming that you do not have the missing pieces though. You will need to create a rough curvature by using the thin wire and tinfoil. This is hard to explain, but you will need to tape the thin wire to the existing sides much like you're creating a 3D model. You can then fill between the wire with tinfoil to give you a workable surface to lay fiberglass on.
Step #5 Lay up your fiberglass the same way that you repaired the cracks above. Allow it to fully cure before removing the wire and tinfoil.
Step #6 The hardest part you will have is the finish work! You will have to bondo the gel coated side in order to fill the gap between the good surface and the fiberglassed areas. This will take alot of sanding and filling. Once you have a good clean surface that matches the original gel coated side, you will need to either brush in some gel coat or paint it. Since the large missing areas are underneath, I would simply get a clean matching surface and blend in some black paint.
I know that this is fairly hard to understand without pictures. I hope that it came across ok, but if ya need any help, kust let me know. Like I said in the beginning, there's a million different ways to do fiberglass. Please do not post that this way is wrong, I've been doin fiberglass for well over 10 years. If you have ideas on a better way of laying it up, please feel free to jump in and write it down. I hope it helps. Sincerely Tony G.