Fiberglass 101

Text and photos by Jeff Stai.

OK, here goes, experts correct me as appropriate!

• First off, DON'T PANIC! If you can build a rocket, you can do this.
• Other first off, SAFETY FIRST! Wear rubber gloves. Be well ventillated or work outside. Wear a dust mask. Wear eye protection. Take steps to make sure you don't get the stuff on you, or on anything else (you know, put down newspaper like your Mom always said ;-). Assume the stuff is poison, kinda like that Bud Light yer drinking, only worse.
• OK, the easiest to try is to glass a fin. When I do thru the wall, and I can slide the fin/motor tube assy up the main airframe (slots cut all the way to the end) I will often glass the fins to the motor tube. When my Magnum blew up, the only part that survived was the fin and motor tube unit.
• After you have done all the assembly AND FILLETS between the fins, motor tube(s), and centering rings, you are ready to glass. Everything is clean and sanded.
• Cut the glass fabric about one inch larger than the fin, with extra along the fin root. Just do one, you're going to do one fin at a time to start.
• Mix a small amount of epoxy. I use the West System with the 5:1 mixing ratio and I bought the pumps; it's really a breeze using the pumps! I mix at most two pumps worth, and usually only one (two is actually enough for a good size body tube.)
• A flat mix dish is best. A dish because the West is a bit runny, and flat because it keeps the stuff cool. Epoxy self heats, which makes it cure faster, and you don't want that!
• Paint a light coat of epoxy onto the fin and motor tube, everywhere the glass goes. Get a handful of those cheap 1" brushes. Yes, you will throw it away, that's why you want the cheap ones! DON'T GOOP IT ON!!
• Gently lay the glass onto the wet surface, pat it down with your fingers lightly; you ARE wearing rubber gloves right?
• Get most of the excess epoxy out of your brush and lightly smooth out the glass, working the epoxy behind it into the weave. RESIST THE URGE TO GOOP MORE EPOXY ON! You want to use just enough to thoroughly wet the stuff, but NO MORE. Excess epoxy will sag, run, and generally be a pain. It mounds and pools and you end up with extra sanding. If the weave is visible but completely wet, THAT'S PERFECT! If all use see is smooth epoxy and no weave, it's too much epoxy!
• Don't leave any bubbles, make sure the cloth is totally flat against the tube, fillet, and fin - that's why you did the fillets first! Any bubbles will have no strength and will break when you sand them.
• Try to curve the excess around the fin edge if you can do that without causing a bubble behind it, but in general you will just leave then hanging past the edge. Resist the urge to trim them before the epoxy dries!
• Once all is neat and flat and you have brushed or pushed off any excess epoxy. Leave it to cure. Sometimes I use a small lamp to generate warmer air. This time of year that can help you get a better cure. DO NOT MAKE THE EPOXY HOT! You just want -warm-. If you hold your hand between the lamp and the wet surface and it feels at all hot, move the lamp back - 18-24 inches is actually good, 6 inches is probably too close. The stuff will bubble up if it gets too hot!
• With the West stuff, after an hour or two, the epoxy is dry to the touch - not sticky like the honey puddles the kids leave on the table for your elbows to find... At this stage, if you work carefully, it can be easiest to trim the glass, and to also remove any runs that got away - my usual is to have a run going down one of the other fins. Quick work now with an X-acto trims it away before it really sticks down.
• When completely cured, about 24 hours, you can sand it. Now, here is the really cool part: you can use a Power Sander!!! Just don't go nuts with the really coarse stuff - try and stay over 200 grit, unless you made a really big booboo! Just beware, you can raise a LOT of dust, so be sure you use a dust table to suck it up. (I got a Black & Decker with a built-in dust bag for Xmas I have yet to try out...)
• What I usually do is do enough sanding to smooth the surface of the glass, but leave it a little scratchy; 220 grit is good. At this point, you can brush on a thin coat of epoxy to cover the weave, or do another layer of glass.
• I don't worry about the fin edges, the epoxy coats seem to make them tough enough.
• After the final thin coat of epoxy (you might need two coats), sand it smooth and you are done!
• Doing a body tube is almost as easy. I do the tube before any construction, cutting slots, mounting fins etc. Don't worry about pre-cut slots, you can easily recut them later.
• The Easy Way is to hang a broomstick on two pieces of string hanging down from the ceiling. Put the broomstick thru the tube, and tie a string to each end. Arrange all this at a comfortable working height - maybe about 'elbow height', more or less.
• Do the same steps as for the fin - cut the glass about one inch too big all around, or more. Plan to overlap an inch or two. Draw a line down the tube for reference. Paint the whole tube, work quickly, start at the line and work around, patting and smoothing like with the fins.
• My overlaps are always kinda messy. I've seen tricks where you get the weave perfectly aligned by plucking out threads, but I'm not that patient. I just do the best I can to smooth out the overlap, and let the Power Sander fix up the fiber blobs...
• I don't know anything about vacuum bagging. You're on your own. Seems expensive and seems to need space...

I think that about covers it. What did I leave out?