DarrelK wrote:There used to be one specific video with a guy using both plaster of paris and just plain old drywall mud for casting on Youtube but it looks like it isn't on there anymore. It's been about 7 years back or so that 80-Grit Guy on this forum was describing how he used drywall mud to make his larger molds. Try and look up posts by him on here. I do mostly fiberglass molding of parts and don't get into these large molds too often. Most of my stuff is "lost foam" casting of original parts that I make, entirely different than what you need to do to replicate a bumper cover.

DarrelK wrote:Once you have actually made the new fiberglass bumper you can usually just make a simple metal sub-frame for attachments. L brackets can be fiberglassed into the back at points, then drilled and connected. Some guys will mold simple electrical conduit tube right into the back of the bumper giving them infinite points to drill into for attachment. With a lot of cheaper kit cars I've had no type of attachment points for the bumper and simply had to block it up in place and then figure out by looking up into it for attachment points.

DarrelK wrote:Ok, let me catch up with you here.... any surface to be molded from needs to be as smooth as possible, taking epoxy out to even 1000 grit would be my minimum.
Ok, your last post is probably going to be the easiest thing to do based on what I am seeing. Looks like a fairly natural modular break in the lines and should work. Again, the goal is to not try and "graft" different plastics together but making sub-assemblies that bolt together works well.