Spoiler:
I’ve always wanted to build a hatch spoiler for this car. The first thing I did was make a template of the contour of the top of the hatch out of 1/4” MDF. Then, when I had it shaped the way I wanted, I made several copies with the table router to create a mold to do the top part of the spoiler.
Easiest way to make a part off this is to glue down some foil and spray it with PVA mold release.
Then I vacuum bagged a layup of two layers carbon and two CSM fiberglass layers.
Then I figured out about how much I wanted it to stick out and trimmed it to match the contour of the hatch opening. Adding holes to access the hatch mounts.
Next I masked off the top of the hatch. The tip here is to plan ahead. Lay down some double backed tape and mask over that. That will create space for adhesive later.
Next I laid down three layers of CSM fiberglass and while it was still wet I added the top layer.
Once dry, trim and check fit.
Next, tape off all the outside surfaces and add two part expanding foam. Then shape with razor knife and sandpaper (shapes easy)
Then I brushed on a layer or two of fiberglass resin to create a skin then bondo smooth
Next, mask off (again) all the outer surfaces and add multiple layers of masking tape around the edges. Then I gently (so it doesn’t crush the foam) vacuum bag two layers of carbon to the bottom.
The reason for multiple layers around the edge is so that you can grind the new carbon back around the perimeter until you get to the tape and the other surfaces will be safe.
Next comes a couple layers of clear gel coat. Interesting note: fiberglass resin is air inhibited. Meaning that it stays tacky when exposed to air so that you can add layers and have them stick to each other. In my experience, if you want a surface cure on your gel coat, you can spray PVA over the gel coat and it’ll seal the surface. Then when you sand the PVA will peel off.
Once it’s sanded flat, I clear coat with automotive clear to add UV protection.
Then it’s time to install. I use a combo of 3M tape (now stick) and urethane adhesive (long term stick).
Rinse, dry, repeat. The whole process took about a week of mornings and evenings in between trying to troubleshoot my cooling issues. It’s not perfect, but it sure is good enough.