Some Thoughts on Sanding Fiberglass

I'll be sanding the entire shell now to get it as smooth as I can.  This operation could wait, but I think it's best to do it before the doors and hatches are cut out.  Quite a bit easier too.

The first thing I did was to sand down the edge where that third layer of fabric laps over the roof.  This will be the only place where 80-grit sandpaper is used.  Right now you can clearly see the edge of the fabric and the sanded area to the left looks dull, but if I temporarily wet it down with denatured alcohol . . .

 voila!, it looks quite a bit shinier and that edge has almost disappeared.  If I could have taken the shot quicker, before the alcohol started to dry, it would be even glossier--closer to what it will look like with high-gloss varnish, but you get the idea.  The round-over will be sanded by hand.  A machine sander will cut through to bare wood very quickly.  The manual recommends a sanding block, but I will be using a sanding sponge wrapped with sandpaper, so it bends around the round-over better.

Here, I am starting to sand the flat portion of the rear deck.  There are some lines I had noticed before which appear to be creases in the fabric, even though I was very careful with it.  There are also shiny spots.  These areas are un-sanded and will be a bit rougher.  Also, varnish will not stick nearly as well.

So the object is to try to achieve a uniform matte surface.  This feels very smooth at this point, sanded with 120 grit.  Eventually I will go over the whole thing again with 220 grit.

And here's that approximate same area wet down with alcohol to give a better idea what it will look like after varnishing.  (You can see some shadows of my finger and head near the bottom of the picture.  I was working fast to get the shot before the alcohol could dry very much.)