THE DARK ART OF COMPOSITES

Part Two (How To)

I started this two-part series by explaining that I once found the mysterious netherworld of composite construction to be unusually frightening. For the unsuspecting neophyte this is a common phenomenon. In an effort to exorcise these demons of infernal torment, I set out to explain some of the main components of composite construction. This time we unveil the ancient rites that must be followed in creating a composite laminate. These descriptions will be pretty simple -- for while I feel confident that I know the ancient dances well enough to convince the uninitiated, I may still occasionally misstep and conjure up a plague of locusts when I really intended to just bring rain.

For general descriptions of various kinds of composite materials, click [HERE!].

Make sure you completely understand the instructions that come with your resins and follow them diligently. The proportion of resin to hardener will vary by product, as will pot life and curing time. Pot life refers to the length of time available to work with the mixed resins before they harden. Curing time refers to how long the chemical reaction takes to be fully complete. There is a period of time right after the pot life has ended where the resin will be green -- the surface is no longer tacky and the resin is a rubbery solid. The excess fiberglass can be trimmed with a regular knife while the resin is green.

Getting Started

1. Trim the cloth to a size slightly larger than the part to be covered. Cut all your pieces before you start.
2. Mix the epoxy resin and hardener per the instructions that came with the product.
3. Spread mixed resin on the part using a cheap brush or roller.

4. Lay on the glass cloth.
5. Use a brush, spreader, roller, or spatula to completely wet the cloth. Brush on more mixed resin as necessary.
6. Use a spreader or roller to remove and all air bubbles under the cloth and excess resin.
7. Perform tribal dance of your choosing while the resin cures.
8. Repeat. The number of layers you build up will depend entirely on the amount of reinforcement needed and the amount of weight you can afford on your rocket.

Next come the finishing steps. The weave of the cloth will be obvious when you finish step nine, and many hobbyists will either sand off the weave or add more resin until the weave is filled. Neither is ideal; sanding hardened resin is real work, and you remove strength as you remove fibers. Additional resin is heavy and doesnt add measurable strength. So we add microballoons -- millions of tiny hollow resin or glass spheres -- mixed with resin this will harden to become both lightweight and easy to sand

9. Combine two parts microballoons to one part resin/hardener mixture to form a honey-like consistency. Apply across the surface of your part to completely fill the weave of the cloth and let it fully cure.
10. Sand smooth.

The vacuum conundrum

Some hobbyists use an elaborate vacuum device after applying resin to their fins or tubes to create a cured part that has no excess resin and no weave pattern to fill and sand. This really works -- but before you invest in vacuum equipment, consider the drawbacks. Its easy to collapse your tube if you arent careful. Also consider the expense. The vacuum method works especially well when glassing an intricate part with complex surfaces, but if the item you are fiberglassing is flat (like a fin) or cylindrical (like a tube), the investment in equipment may be more than you need.

Instead, try this bit of glassing magic that is both easy and cheap and reduces the sanding and finishing work to almost nothing:

Before you start, cut a piece of ripstop nylon slightly larger than the item you are laminating. After youve worked out all the air bubbles in your glass cloth, apply the ripstop nylon to the surface of the wet resin. Use a wadded paper towel to remove bubbles, smooth out wrinkles, work the resin up through the ripstop nylon, and to soak up any excess resin. Let the resin cure until it is green, then peel the ripstop nylon off of the surface. There will be no discernable weave pattern in your work, only the fine texture of the ripstop nylon! This is easily sanded smooth with little or no additional preparation. Caution: make sure the resin is sufficiently cured so you dont pull up the fabric, but not so far cured that the nylon cant be removed.

Other Tips:

• Use vinyl or latex gloves, and put on two pair. You can strip one pair off if you need a clean hand.
• When glassing Kraft tubes, remove the Glassine (shiny) layer first. Resins dont adhere well to Glassine.
• Select a hardener with a pot life of at least 30 minutes. You dont want your resin to set up before you finish your lay-up.
• Mix the resin/hardener thoroughly. When its fully mixed, stir it again. Repeat.
• Click [HERE!] for a write-up on the Fiberglassing Rotisserie Stand.
• Click [HERE!] for a write-up on the High-Speed Tube Sander.
• Chanting, whirling, and self-mutilation are purely optional. The use of goats blood and chicken feet are not recommended.