Creating Fiberglass Components Using the Lost-Foam Method

The lost-foam process starts by creating a plug or blank out of foam and applying fiberglass cloth and resin directly over it. Once cured, the foam is manually removed or dissolved using lacquer thinner or acetone leaving only the fiberglass shell behind. Advantages – The foam is readily available at local hardware stores and is easily shaped using simple tools and sandpaper. Also, there are no complicated molds to build. Disadvantages - You can only create one-off pieces since the blank is destroyed.

There are two basic types of fiberglass resin. Epoxy resins - Low odor and ideal for layup use. They provide high strength, low shrinkage and low brittleness. They can also be used as an adhesive when used with filler or micro-balloons. Polyester resins - Less expensive than epoxy but have toxic fumes which require use of a chemical respirator. Polyester resins are more brittle than epoxy and are not foam-safe. Types of Fiberglass Resins

I use West Systems 105 Epoxy with a 206 slow hardener. Working time is about 90 minutes with a recommended temperature range 60 to 90 degrees F. The hotter the temperature is the faster the cure time will be. West Systems also offers 300 series Mini Pumps which are designed for convenient and accurate metering of epoxy resins and hardeners. They mount directly on the resin and hardener containers and eliminate the mess involved with measuring by weight or volume. The pumps are calibrated to deliver the proper working ratio with one full pump stroke of resin for each one full pump stroke of hardener.

Fiberglass resin can be messy and toxic. Carefully protect your floors, work areas, as well as yourself. Cover the floor with plastic sheeting and wear protective eyewear and gloves. Always work in a well-ventilated area. A particle mask is recommended when sanding cured fiberglass cloth.

Dense, pink, grey, or blue foam insulation board is easy to carve and holds its shape better during layup and sanding. It is commonly found in local hardware stores and is comes in sheets of varying thickness. Glue foam sections together to create a large blank. However, be aware that the glue lines will not have the same density as the foam and will be more difficult to remove. This can leave ridges in the finished blank. Use standard shop tools (knives, saws, etc.) to get a rough shape and then use drywall sanding pads to finish sand. For round pieces, use a drill press to function as a vertical lathe and shape with sandpaper of different grits until the proper shape has been created. The dimensions of the blank should be slightly smaller than those needed for the finished piece due to the additional thickness of the cloth and resin. Take this into account when creating the blank. Cover the surface of the foam with clear packing tape if you plan to remove it after finishing. Otherwise you can apply the fiberglass directly over the blank. Making the Foam Plug

Cut the cloth material to shape prior to applying epoxy. Make sure to leave ½ to 1” of material where it overlaps another piece. It will make it a lot easier to create a smooth finished surface if the cloth is precut to conform to the contours of the blank. Mount the blank so you have easy access to all surfaces. For example, use a nail on each end to hold it above the work surface or use a rotating mount when working on round pieces. Apply one layer of 2oz or 3oz thick fiberglass cloth or wallboard tape, using 3M#77 spray to hold the cloth before the epoxy is applied. Mix your epoxy per the manufacturer's recommendations. Brush epoxy into the cloth, thoroughly saturating it, using a dry brush or squeegee to remove excess resin. Apply additional layers of cloth and resin as needed until you get the thickness and rigidity needed. Allow the epoxy to harden for 24 hours. If additional layers are needed after 24 hours then you should roughen up the surface with sandpaper first. Fiberglass layup

Removing the foam is easy but can be messy. Simply pour small amounts of lacquer thinner or acetone on the foam core over a disposable paint tray or bucket. The foam will melt away and leave a hollow shell. If weight is not a problem you could leave the foam core in place as it provides some rigidity. Removing Foam Core

After the epoxy has hardened, rough up the surface with medium sandpaper. Mix up a blend of epoxy and filler so it is just liquid enough to be brushed on, but no so fluid as to be runny.. Brush the filler all over the blank and let it harden until it can be sanded. Don't let it harden any longer than necessary, because it just makes it more difficult to sand. Using sandpaper of decreasing roughness, sand all the mixture off, except what is left in the hollows. One application may be enough to get a smooth surface, but you may have to touch up a few areas. Spray with primer. Wet sand almost all of it off. Repeat this until you are happy with the surface smoothness. Finish with two coats enamel. Finishing

Project #1 Estes QCC Explorer Upscale Nozzle

Project #2 Iris Booster Nose Cone

Project #3 Sky Cycle POC Headrest