How to Fiberglass like a Pro

Fiberglass, as a term, is really a misnomer. Fiberglass is one of the many materials that can be used along with resin (plastic) to create a strong and light structure.

In truth what most people call fiberglass is properly referred to as Fiberglass Reinforced Plastic (FRP). It is also a composite material, much like Carbon Fiber Reinforced Plastic (CFRP) today. FRP predates carbon fiber by at least seventy years.

One of the earliest uses of FRP was by the military in making helmet liners. (see picture at right for a World War II liner)

After the war returning GIs began experimenting with the material in the form of car bodies and boats. Sailboats first and later powered watercraft. Because so little was known about the strength of FRP in those years boats and car bodies made then are still around today. Almost indestructible in their strength.

In many ways it is an ideal hobbyist material. With a bit of patience it is fairly easy to use with most of your effort going into preparation not actual creation of the item. No special tools are needed. In fact I recommend using old food containers to mix the ingredients in and purchasing or using cheap bristle paintbrushes and dowels for applying the resin.

FRP can be used to make auto repair, boat repairs, or even to create new structures that have not existed before. It is also possible to use FRP to create molds for FRP objects.

Fiberglass is the actual cloth or mat made up of glass fibers. List below contains common designations for this material.

• Woven Roving
• Glass cloth (AKA bi-axial)

• Woven fabric (AKA bi-axial)

• Glass mat, this material has no weaving or set orientation
• Knitted fabric has the typical cloth pattern with additional runs of fiber at forty five degree angles.

Well, almost everything. You'll need the right weather conditions, the right tools, and the right surface preparation to get a qualilty job. Likely, you'll also need to know how long it takes for a piece to cure, when you can add to it, and how to protect it once it's finished.

Weather is very important. Ambient temperature should be between sixty (60) and eighty-five degrees (85) Fahrenheit.Tempertures below sixty will mean extremely long cure times or no cure at all. In fact if ambient tempratures are at or near freezing the resins won't set.

Relative humidity should be below sixty percent though epoxy is not as suseptible to humidity. You do not want to layup an FRP job in the rain. Trapped moisture will not stop the curing process or even slow it down, but water bubbles in your layup can cause the lamination to come apart months or years later. This in turn will compromise the strength of your creation so just avoid it if possible.

Basic Tools: You'll need sandpaper, acetone or denatured alcohol, tack cloth, distilled water, glass cloth, resin, mixing containers, and a roller. Patience too.

Tools are probably the cheapest part of this. The cloth the next cheapest and the resin the most expensive. I strongly recommend using Polyester resin for this first attempt. it's easier to use and much more forgiving.

Safety Wear: Since the resins are hard on your skin you'll want to have latex or nitrile goves and eye protection. Nothing fancy for the eyes you just don't want the resin to splash into your eyes. Since the cloth and mat are fully formed you shouldn't have to worry about getting fiberglass particles on your skin. A long sleeved shirt and blue jeans should be fine.

Cutting: I recommend an old pair of scissors. The cloth is much harder to cut with a knife though it can be done.

Mixing Containers: Of course you'll want an accurate measurement of your liquid components, but you can get an inexpensive measuring cup at a paint or hardware store.Save your money on mixing containers. Since you don't want to start out with a huge job you can do this with old margarine tubs, or other used food containers. Just be sure they are clean and dry. This way you won't feel bad throwing them out afterward either.

Spreading/Leveling Tools: Use old cheap paintbrushes or the cheap synthetic paintbrushes. The brush does not have to be the same high quality you'd use on a paint job because all you'll be using it for is moving the resin around. Do not use a foam brush; it will melt with polyester resins.

You'll also want 1/2" thick wooden dowel material to serve as a roller. You'll use this to make sure all the air bubbles are out of your work. You could buy a specialized fiberglass roller, but they cost more than dowel, are harder to clean up, and are only worth the cost if you plan to do this pretty often. Wooden dowel, on the other hand, can be cut to the right width (about six inches) and thrown away without much worry.

Sandpaper: You'll want a 60 grit and a 120 grit at least. If you are doing finish work (work that will be painted) use higher grits in the 300 and 400 range.

Solvents: Like acetone and/or denatured alcohol are used to degrease and clean the areas you are going to fiberglass. Oil and grease will prevent the resin from sticking (hint) so you don't want any residue, not even from your hands, on the area to be fiber-glassed. Acetone will remove most types of paint so start with alcohol until you gain some experience.

Final Cleaning: Your final cleaning will require a tack rag and distilled water and lint free cloth. This is probably not really necessary, but I always go this extra step and have never been sorry.

This is basically what you'll need. Oh, and the reinforcing fabric and resin of course.

First: Figure out how much resin you are going to use (assuming polyester). If you are fiber-glassing a one foot square area figure on one cup of resin and however many drops of hardener recommended by the manufacturer. Do not prepare the resin yet.

Assemble the tools you'll need. Cloth, resin, gloves, glasses, measuring containers, dowel or roller, sandpaper, alcohol (denatured), water, clean lint-free cloth, and paintbrushes.

Second: Prepare the surface to be fiber-glassed. You want to use a rough sandpaper and remove any paint, varnish, and/or dirt. It's best if you sand right down to the original surface. You can use a power sander if you wish. You do not even have to get the surface particularly flat.

Third: This is the point at which you want the gloves and safety glasses. Clean the surface. You want to vacuum it or use denatured alcohol on a lint free rag to get any of the sanding debris off. Do this two or three times to make sure that the surface is perfectly clean.

Fourth: Clean the surface a final time with distilled water and a lint free cloth. Let air dry or blow dry with compressed air. Use the tack rag last to make sure every contaminant is gone.

Fifth: Cut your cloth to the size of the repair. The easiest way to do this is to cut the cloth, hold it to the repair area, and trim some more as needed. Set the cloth aside on a clean work surface.

Sixth: Prepare the resin. Following the manufacturers instructions pour the resin into the measuring cup to the recommended amount (see above) and carefully add the hardener drops. Stir this mixture thoroughly and slowly. Avoid churning air into the resin. You'll notice it's about the consistency of syrup. If you are using epoxy then you are looking at a half and half or possibly two (2) parts resin to one (1) part catalyst.

Seven: Apply a layer of resin S.L.O.W.L.Y. Because of the viscosity it will tend to run off of your paintbrush in long strands and get everywhere. Working with it slowly will ensure it goes where you want it to go.

Eight: Apply the cloth layer (You should have your gloves on remember?) and press it into the resin with your fingertips. It should stick readily. Now, add more resin on top of the cloth working from the center of the cloth outward. As you do this look for air-bubbles and use the paintbrush to brush them out. Use the dowelling if necessary to press the resin/glass sandwich together and remove any air bubble. Bubbles are bad; they weaken the composite.

Nine: Wait! Curing will take from two to four hours depending on the resin. Check the manufacturers label.

If you are planning to add another layer watch this cure time closely. The resin will cure to a hard, yet sticky state after the prescribed (two to four hours) amount of time.

When the resin is hard and sticky is the ideal time to add another layer of resin and glass without any preparation. Mix another batch of resin, apply it, the fiber (cloth or mat) and more resin. Roll out the composite with dowel and wait the prescribed curing time. You can do this many times as long as you add the next layer before the resin cures to a non-tacky surface.

If you let the resin cure for a full twenty-four hours you will have to sand it and clean it as outlined in the third and fourth steps above.

If it's getting late in the day and you have leftover pre-mixed resin it can be put in a covered container and stored overnight in your freezer. It will not cure at or near freezing. The next day pull it out of the freezer and as soon as it thaws use it.

Using the method described above successive layers of glass and resin can be layered, ending with glass mat for a paintable surface. I strongly recommend using a primer then finish paint for a professional look. Paints should be polyurethane or two-part epoxy. The two part epoxy paint is tougher, but harder to come by (some states now ban it's use by all but certified professionals). Epoxy paint is also better for "immersion service" e.g. use below water.

Note that the pigment (and often additives) in the paint prevent epoxy based paints from reacting to ultra-violet or sunlight.