FIBERGLASSING FOR MODELERS
(Part 1)

By Cecil Collum

Safety First!

Fiberglassing is a fast, easy way to strengthen an airframe or to create lightweight, strong parts. There are some dangers associated with fiberglass and resins, so let's briefly go over them and some countermeasures we can take to protect ourselves. Fiberglass and Epoxy materials present a potential safety and health hazard if we don't follow the proper procedures for working with them. A few safety basic considerations are fumes, MEKP, gloves and eyes.

Polyester resins all have a distinct odor about them; that odor is the Styrene Monomer in them. Acetone, MEK, many solvents, and gasoline all have distinct odors and they should warn us that the liquids are probably flammable and we shouldn't breathe much of them. When working with materials that give off potentially hazardous or flammable fumes it's important to work in a well-ventilated area.

The best protection against these fumes is an Organic Vapors Respirator. This is normally a full-face mask with replaceable cartridges that absorb organic vapors. Always store your respirator in two plastic bags to prevent their absorbing odors after you are finished for the day. Learn how to check the valves in your mask; if they are damaged, they will leak. One easy check is to don the mask and spray or pour some lemon oil close to the mask. If you smell the odor, your cartridges are no good and must be replaced prior to continuing.

MEKP is an acronym for Methyl Ethyl Ketone Peroxide and is the catalyst for most polyester and vinyl resins. Be extremely cautious when handling this stuff; if you get it on your skin, you will get a chemical burn. If you get it in your eye, it can blind you! ALWAYS TREAT MEKP WITH RESPECT AND CAUTION! Also, don't confuse MEK and MEKP. MEK is a solvent; they look the same but smell different.

Wear gloves while handling fiberglass and resins. Any one of us can develop an allergy to these chemicals at any time and most will develop an allergy if exposed over time. Epoxies are especially damaging to the skin and once you become sensitized to epoxies, you won't work with them again. Latex gloves are an inexpensive and simple solution to hand care. Nitrile gloves are available for anyone sensitive to latex. Avoid the clear vinyl gloves used in food service, they will dissolve when styrene or acetone hits them.

Eye protection is a must for fiberglass work. Many people have been blinded over the years by chemicals (MEKP) or objects thrown from a grinder. We only get one set of eyes and when they are gone, they are gone for good. I personally like a full-face shield for this operation. Wear safety glasses, which are made of shatter-resistant material and have side shields to protect against objects thrown from either side. DO NOT WEAR REGULAR GLASSES! They will shatter and become imbedded in your eyes.

Let's recap safety:

• Safety is an attitude as well as a way of doing things.
• Safety is a way of looking at a job or situation and recognizing potential dangers and avoiding or preventing those dangers.

It really doesn't matter how experienced or skilled we are, machinery and chemicals don't know or care!

Now let's discuss resins:

There are two basic kinds of fiberglass resins:

1. Polyester, and
2. Epoxy.

Polyesters are commonly used in boat building, storage tank, construction, hobby projects (finishing resin) and many other products. They are inexpensive to buy, easy to use and have predictable characteristics. Most polystyrene resins have a distinct odor caused by the styrene monomer added to dilute the very thick base resin. The smell is quite strong and can overcome a person in a short time so wear your respirator and ventilate the work area when using polyester resins.

Polyester resins are called thermosetting plastic resins because heat causes them to set up and cure. They will actually set up in the can in 3 to 18 months, depending on the type of resin. Most jobs have to proceed at a faster clip than this, so we add a catalyst to the resin to obtain a much shorter set and cure time.

The most common catalyst is Methyl Ethyl Ketone Peroxide or MEKP for short. MEKP reacts with other chemicals (promoters) that have been added previously to the resin. This oxidation reaction generates internal heat and causes the resin to begin setting up. This process is called "polymerization." Once the resin has set up it will remain hard and cannot be softened by heating. It's very tough stuff!

We can control the time it takes for the resin to go from a pourable liquid to a gel, and then to a solid, by varying the amount of MEKP added and also by adding external heat or cold. The reaction is very controllable and predictable, as a general rule, and can vary somewhat depending on the individual resin you are using and the amount of "promoters" added.

Polyester resins "catalyzed" 1% by VOLUME (or 6-8 drops of MEKP per ounce of resin) equals 20-25 minutes working time @ 72 degrees Fahrenheit. Remember, polyesters are very controllable. The reaction we saw previously was at 72 degrees F.

What if the temperature is hotter or colder? Let's say the temperature is 54 degrees F. The resin is now much colder and has less heat than before and has less heat to begin with. It has less ambient heat. If we double the catalyst amount to 2% by VOLUME (12-16 drops of MEKP per ounce of resin) we find that the working time is about the same - 20-25 minutes.

The extra catalyst caused a "hotter" reaction that compensated for the colder resin temperature.

Now let's suppose it's warmer than 72 degrees F., say it is 90 degrees F.: The resin is now warmer and has more ambient heat. You have probably guessed that if we halve the MEKP to ½% by VOLUME, 3-4 drops per ounce of resin, the working time remains the same. Since the resin is hotter to begin with, we didn't need as much catalyst to get the same reaction and working time. Remember, these are approximate ratios and times. If uncertain, run a test batch.

One other caution, these times are based on using 3 ounces of resin. If we catalyze a gallon of resin and leave it in the pot, the working time will be shortened because of excessive heat. If we spread that same gallon in a thin layer, increasing the surface area, it will dissipate the heat faster and working time will be lengthened.

This is not an exact science but with a little practice you can predict your working times and catalyst ratios very close. In very hot temperatures you may have to use ½% by VOLUME of MEKP and work very fast, whereas in colder temperatures one may be tempted to keep increasing the MEKP but this is not a good solution. You may increase the ratio to 3 or 4% but you are better off adding some external heat to speed the reaction. Too much catalyst can cause excessive exothermic (heating) action and cracking; the resin will literally cook. Too little catalyst and it may not set for months, if ever. When in doubt, try a test batch!

Next month we will discuss epoxy resins, which are stronger than Polyester resins, but more difficult to sand.