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Let's Play With Fiberglass

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It has been thought that making parts with fiberglass has to be performed by the experts. With a little practice, very little practice, anyone can be an expert - literally. There is no black magic to laying fiberglass, the old stereotype itching from the glass fibers is not an issue for the most part, it's not difficult, compound curves suddenly become easy to produce, the finished parts are light weight and strong (some stronger than steel), and most of all easily produced and modified. Hopefully this will give a description in enough detail that anyone can produce fiberglass parts that will meet their specific needs with minimal work and expense. Chopped fiberglass requires special equipment to apply and will not be addressed here. Also, the application of gel coat will not be addressed here.

First we need to define some terms so everyone understands the language that will be used in the discussions.

Lay ups
Lay ups is the process of laminating the fiberglass into the desired shape. A lay up can be anywhere from one thickness of fiberglass to 1000 layers.
Each layer of fiberglass is referred to as a "ply". If we refer to a 4 ply lay up there will be four layers of fiberglass.
These are the "glues" that hold the fiberglass together. For calculation purposes the resins/epoxies contribute no strength to the part.
UID Fiberglass
UID implies the fibers of the glass cloth run in one direction only. There is a small thread of glass strands that is interwoven but that threads sole purpose is to hold all of the fiberglass strands, or "toes", together. This type of fiberglass cloth is very strong in one direction only - parallel to the direction of the glass fibers.
BID Fiberglass
BID implied bi-directional, fibers running ninety degrees to each other much like regular cloth. This type of glass is very strong in two directions because the concentration of "toes" is in the two directions. For most applications this type of fiberglass cloth is used with the glass being cut along the "bias", or at forty-five degrees (45°) to the fibers directions. This is done for strength.
If we take cotton fiber and chop it into almost a powder we get flox. Flox is used for some structural areas where a hard corner or hard point is required. The flox is mixed with resin or epoxy to a paste consistency and then applied to the area requiring the added strength and hardness.
Little tiny glass beads, microscopic in size, very light weight, absolutely no structural strength, that's "micro". Micro is used when fiberglass is applied to a foam mold where the foam is part of the structural make up of the part. If you look at styrofoam you will see the foam cells are all open (open cell foam). If resin/epoxy is applied to the foam and fiberglass is applied over it the small cells in the foam will have to be filled with the resin/epoxy before the fiberglass cloth can be "wet out" with the resin/epoxy. The result is a heavy piece with poor structural properties. If microshperes are mixed with the epoxy first and then squeegeed onto the foam the result is a light weight filler that helps hold the fiberglass to the foam - a mechanical bond of sorts. When micro is mixed with the resin/epoxy the resultant mixture is referred to as "micro-slurry". Depending on the amount of micro added to the resin/epoxy determines the consistency of the micro-slurry. For most applications where the Styrofoam is being filled a "peanut butter" consistency (smooth, not chunky) is best. A very dry mixture can be used for surface filling and contouring.
Peel Ply
This is the "poor mans gel coat". Peel ply is nothing more that 100% dacron cloth, like lining material or shower curtain material. It needs to be 100% dacron, no substitutes. Also, weaves like "blouse weave" is a no-no, hard to get off. I like to use a off color for my peel ply as it's easy to see, I can be sure it's all removed before the next step. The use of peel ply will simplify finishing ten-fold.
Mold release
When we want to form fiberglass but don't want it to stick to the mold - what ever that may be, we need a mold release. Plastic packaging tape (clear or brown), duct tape, plastic, what ever works well. I like duct tape and good old 6 mil plastic.

You need some tools to do the work. I would recommend the following:

  • 36 grit cloth backed sandpaper
  • Butcher knife
  • Stanley Sure Form
  • Files of various cuts
  • Air compressor
  • Nylon disposable gloves
  • Hacksaw blades
  • Duct tape
  • Rasp(s)
  • Dremel (optional)
  • Shop vacuum
  • Latex disposable gloves

Please note, the nasties from the resin/epoxy can pass through latex gloves, latex gloves are porous. I like to wear nylon disposable gloves (Wal-Mart specials) with latex gloves over them. If I need to do big lay ups where I will be hours I don butyl gloves and put latex gloves over them to protect them as the butyl gloves are $$$. Take what ever measures are possible to keep the resin/epoxies off your bare skin, these compounds can be very nasty with long term exposure - ask me how I know.

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