The Choprical Fish: a Human Powered Party Bike

Step 25 Sand and smooth fiberglass surfaces using a gel coat.

By this stage in the process, you have finished the structural and functional aspects of your party bike. It's time to work on the visual details, like smoothing out the surfaces. If you use fiberglass on the outside of a positive form, as I have done, then the exterior surface will have the texture of the fiberglass fabric, similar to the texture of a cast on someone's broken arm. This is generally considered 'unfinished'. It's strong enough to use and test, but it will not look good, either painted or unpainted. In order to have a smoothly faired surface that you can polish or paint, you need to use a gel coat, and then sand till you're satisfied.

A gel coat is basically a thicked epoxy coat that includes no fiberglass. You paint or smear it on the fiberglass. Then 24 hours later, you sand it down. In my case I repeated this procedure 3 times. In the photo you can see that in a couple spots, I was sanding all the way through the gel coat to the fiberglass fibers. This is a no-no, since it means you are sacrificing strength. If you aren't happy with the curve yet, and you're sanding down to the fibers, you have to add more gel coat, then repeat the sanding process.

Most fiberglass products handle the gel coat a little different. Take a fiberglass boat, for example. Instead of laying up the fiberglass over a positive form, they would lay the fiberglass inside a negative mold. Before adding fiberglass, they'll paint in a gel coat. This way, once the glass hardens, they can pop it out of the mold. The gel coat, which was touching the inside of the mold is now the exterior surface.

In my case, the complexity of dealing with male - female molds, was greater than I wanted to take on for my one-off Soul Cycle. So I had to deal with sanding and gelcoating repeatedly.