Let's Play With Fiberglass

by Steve Sharp

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Okay, let's do it, we're ready. Let's see, let's build something. Remember those gaping holes that had to be cut to clear the headers? Well since the headers have been redesigned and the gaping holes are no longer needed you need to close them up. Also, you need a couple of bumps were we didn't have them before. The mission at hand, make some patches that will close the gaping holes and allow extra clearance where it's needed, piece of cake.

First you need to select your mold material. I have found the urethane foam available in hobby stores to work very well. This is the green or brown crumbly stuff that comes in bricks usually 3" X 4" X 8", six bricks to a package for about $3. I like to build up an oversize block using the bricks in alternating positions secured with adhesive. I have found 3M 77 Spray Adhesive works very well, spray it on, let it dry (contact type cement), stick the blocks together until the appropriate sized block is created, and start shaping. Sanding and knife cutting is probably the best. DO NOT TRY TO HOT WIRE - TOXIC FUMES WILL RESULT.

Something else that works well is "Pour Foam" which is a two part urethane foam used in taxidermy and in building boats. Check with your local boat builder/repairer, they may have some you can play with. Small batches here as this stuff billows to about 30 times it's liquid size. It cures in minutes and can be shaped once the foam has cooled. Cutting is accomplished with a knife, sanding, saw, whatever. This foam cannot be hot wire cut.

Another product that works okay is the "foam in a can" insulation available at home centers (Great Stuff). The problem here is the foam takes about twenty-four hours to cure and is spongy when cured. This makes shaping more difficult. Also, it is tends to have large voids which can lead to problems, I use it only as a last resort. It can be shaped with a knife, saw, sandpaper, rasp, and file. Hot wire cutting is not an option.

Another ideal product is Styrofoam (blue foam). This can be cut with a hot wire - very accurate, can be sanded, cut with a knife, filed, rasped, sawed, however you want to cut it. More on this at a later date.

Time to start, Pour Foam is the foam of choice for this application. Since it can be expensive you might consider throwing in a filler block of the green urethane foam as well. The foam will be totally discarded when the pieces are made so the properties of the material need to be easily shaped - that's it. There are no structural considerations to think about. While you're at it you remembered you need a couple of round tapered "bumps" to clear the mufflers. A piece of four inch cardboard tubing will work, just a few simple bandsaw cuts and some hot melt to hold the pieces in place will do.

Step 1

Mount the cowling in place and using duct tape and pieces of cardboard construct some dams that will reduce the amount of foam required and also keep the foam off of any components that don't need foam all over them. Some plastic also helps keep things neater. Just a cut-cut here, a whack-whack there and the dams are done. The dams are not pretty, but then who cares, this is purely functional.

Step 2

Mix up the Pour Foam and pour it into place. I love to watch this stuff expand. While you're at it why not pot in a couple pieces of urethane foam blocks into place and pour the Pour Foam around them securing the urethane foam into place. This saves time and money.

Step 3

Foam is cured, time to carve. Tools of choice: small saw, butcher knife, rasp, Stanley Sure Form, 36 grit sand paper. The foam is shaped and contoured to smooth curves and faired into the areas where bumps are needed. Taking your time is critical here, symmetry is important. Make a mistake, mix up a dab of Pour Foam and fill it in.

Step 4

Sweep up the mess and admire the handwork. Total time so far, maybe one hour. Since the foam will be discarded when all is done you need to apply the mold release - duct tape. The entire foam surface is covered trying to retain the compound curves you were so careful to make, trying to prevent making any folds or creases in the tape, lots of duct tape. The tape needs to extend out onto the actual cowling for attachment later. You need to allow an extra couple of inches for this.

Step 5

Cut the fiberglass cloth to fit. Cut the glass oversize allowing about 2" overlap on all edges, this will be trimmed later. Cut as many plies as needed. It's okay to splice pieces together, allow about 1" overlap at each splice. Splicing sure saves glass!!

Step 6

Time to get messy. Mix up some resin/epoxy per the instructions. When thoroughly mixed using a small disposable paintbrush coat the duct tape with the resin/epoxy, a light coat is okay. Place the 1st ply of fiberglass cloth on the duct tape and smooth out getting the cloth worked into and around he compound curves. The cloth will absorb some of the resin/epoxy, using the brush apply more resin/epoxy until the surface is coated and there are no white spots visible. Ply one is now wet out.

Lay down the second ply and work the resin/epoxy up through the second layer with a squeegee and a stippling action with the paintbrush (a light stabbing action). Don't apply any additional resin/epoxy yet. A hair dryer and localize heat help reduce the viscosity of the resin/epoxy and aid in wetting the second layer out.

Repeat for the third, fourth, and fifth layers. Make sure all of the sir bubbles are worked out with the squeegee and the stippling. A small bubble here and there isn't an issue, a large one is and will present problems later on, get ‘em out now while you still can. A thin coat of resin/epoxy should be applied to the just wet out layer in preparation for the next ply. Remember, there is no strength in the resin/epoxy, it's only the "glue" holding the fiberglass together. All of the strength is in the fiberglass. It's better and lighter to have the excess resin/epoxy on the floor than on the piece.

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