Fiberglass adds strength to the rocket, but it also adds the need for some finishing work. Fibrglass resin leaves pits in the surface wich need to be filled in. I use a profesional glazing putty made by Bondo and available at any local auto parts store. This putty can also be used to clean up the transition between sections of fiberglass and fixing the transition between the fins and airframe. After sanding the rocket it is time for primer. I use 2 coats of a sandable filler primer and finish the preperation for paint by sanding the entire rocket with 400 grit sand paper.