Composite Building Newsgroup

[cub builder]

Hello Bob,

One of my big hang ups is the finishing process. I've taken the EAA's two day seminar on composites and the short one at Oshkosh (a couple of times). These were great for the learning the basics of layups and joints but they didn't go over the finishing.

One of the first steps in my Jabiru construction manual was to sand down the interioir of the pre made fuselage. They stated this is needed to clean up any rough fiberglass that might cut or scratch you in the building process. I couldn't help myself; I turned a three hour sanding task into 30 hours of turd polishing.

I'm also concerned that I might leave things too rough and regret it when it is time to do the finishing.

As as you can imagine, not knowing where I should be on the "make it smooth" or "slap it together" scale has me somewhat paralyzed in my kit building progress. Any advice?

I also have questions about: fuel tanks, hard points, trim tabs, and other misc items.

Ill look into getting Andy Marshall's book.

As previously mentioned, avoid sanding into the weave of the fabric.

Be fearless when working with fiberglass. There is nothing you can screw up so badly that you can't grind it off and build it up again.

When finishing, use a cheap rattle can of spray on primer to check your work. If you think it looks good, or you want to see how good (or bad) it looks, spray a light coat of cheap primer over the part. All the imperfections will suddenly come into focus. You're going to sand off the primer anyway, so there is no need to use an expensive primer.

Pinholes are easy. I brush on a coat of really cheap Rustoleum high fill primer bought at the local autoparts store. Then I brush on some more while it's still wet. Then I brush on some more again while it's still wet until I have a half dried slurry of primer. I squeegee the primer back and forth over the pinholes until it starts to get too thick to work. Let dry for 30 minutes or so, then wet sand with 220 wet. Again, expensive primer isn't required as you will sand off everything except the primer that is left filling the pinholes. After wet sanding, shoot a light coat of cheap rattle can primer as it will show any remaining pinholes. Wet sand the cheap primer back off, and repeat the process if you still have any pinholes. It's inexpensive, and quick.

Finish on fiberglass is never perfect. You just reach a point where you are tired of sanding and want to fly, so you prime and paint.

Feel free to peruse my personal web site as there are some areas that cover a lot of glass work that I've done when modifying the KR that I built many years ago. I never put the original photos on line from when I built the plane as photos were still done with film back then, so I didn't take as many and never scanned the ones I have in for the web site.

-Cub Builder