Good apprach. If the area is pretty broken up, you can reshape it by
hand, use masking tape on the top surface to hold it together. Go
behind it and grind it out with 220 grit. Reshape it with your hand
and then paint a little resin in there. Place your already cut to
shape and size cloth on the wet resin. Take a cheap paint brush and
brush your cloth flat again with more resin. Using the paint brush
helps you get any air out and carefully lay the new cloth flat,
brushing it out flater. If you need a second underlayment of cloth,
do it the same way now. Before it really sets, you can reshape it
with your hands. The closer you get it to it's final shape, the
thinner your repair will need to be. I've gotten them right on
perfect by working it wet. Let that dry and harden. Now your ready
to go back on top to the original fiberglass which may have cracks
from impact. You will want to take a die grinder (I use a dremel)
and gently cut out' carve out every crack that is in the fiberglass
mat to make a little V. On most glass cars this winds up being a V
about a half inch wide. Basically you are taking a tiny crack and
widening it from that crack down in the bottom of the V to .5 inches
wide at the top so that you are going to reglue/repair it with a
wider/stronger patch. Every significan crack must be ground out to a
V and repair to return the panel to it's original strength. I've
seen guys try to glue two broken pieces together on race cars and
they are recracked within three or four races. (Ok, it was me and my
brother). Basically, we learned that it just takes a little longer
to do it right the first time. For the little crack channels, you are
going to want to cut up some of that fiberglass mat into little .25
and .33 and .5 inch hairs, mix it with some resin and paint it into
those channels. Keep a little of the mat on the side. Dab it into
the channel, and keep a little resin only on the side, also to paint
it in. Be careful not to get too much outside of the channel because
you are going to be sanding it all back down to a finish surface.
Also, don't mix your resin too hot (with too much hardener). If you
do it will dry too fast and be too rigid when you are done. You want
it to be a pliable repair. Once you get your repair structurally
fixed, you are going to want to go over the final surface with a
thinner, flexible fiberglass repair like bondo. (Others will
complain if I say MarinTech. And then the final finishing with
sandable primer. When you get the repair surface both smooth (not
wavy) and no pin holes, your ready to go to paint. I would advocate
at least a 6 inch flat block sanding to make sure you don't have
waves. You can use a guide coat, which is misting black paint over
the grey or red primer, then sanding. When you sand off the all of
the black with a flat 6 inch long block without seeing any black in
the "lows", you'll know you got it flat and not wavy.
