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What is Fiberglass?

Fiberglass is a composite material widely used in the automotive industry, kit cars are often made from fiberglass as are many sports cars including the Chevrolet Corvette.

Fiberglass is an incredibly versatile material and it comes in several forms. Almost everyone has seen fiberglass insulation and anyone who has touched it will recall the itchy feeling often with a little rash which develops afterwards. This Is because the minute shards of glass cut into the skin and cause irritation.
The fiberglass used in the automotive industry is different from insulation fiberglass. It usually comes in a mat, tissue or cloth, although a chopped strand mixed with resin is often used for large applications such as boat hulls.

Working with Fiberglass is an unpleasant business due to the fumes from the resin and itchiness of the fiberglass. Whenever you are working with fiberglass use gloves, overalls and a respirator, take frequent breaks for fresh air if you are in a confined space. To reduce the itching of fiberglass try not to scratch . Instead wash the affected areas gently with cool water as often as possible.

Gelcoats are the shiny face of fiberglass, gelcoats are what you see on most fiberglass vehicles (which haven't been painted) or boat hulls. Gelcoats consist of a thick gel-like resin mixed with a colored pigment, it is the first thing laid into a mold and therefore when the mold is removed it becomes the exterior.

Below is simple diagram showing how many fiberglass bodies are constructed, there are other methods and this is just a common example.

fiberglass tissue

Fiberglass tissue as the name suggests is a very thin tissue like layer of fiberglass, it is very smooth and porous and the tissue sits underneath the gelcoat. Tissue helps to smooth out the inherent roughness of fiberglass matting, while also adding strength.

fiberglass mat

Fiberglass matting makes up the bulk of any fiberglass bodied car. Several layers are built up one on top of another until the desired thickness and strength is achieved. This is what you might see if you look at the inside of a fiberglass panel.

fiberglass cloth

Fiberglass cloth is strong and is often used where it may be visible and therefore aesthetics are important. One of the downsides of fiberglass cloth is that because the strands are neatly woven the layers do not intermesh like they do with the disorganised and loose strands on the fiberglass mat. Therefore the layers of cloth sit on top of one another, rather than meshing together like the fiberglass mat.

Resin and Hardener
Without resin the fiberglass itself would be useless for building anything requiring rigidity. Resin is mixed with a catalyst before application to the fiberglass. The drying process involves a chemical reaction which has several variables including, the amount of catalyst, temperature, humidity, and any water present in the fiberglass resin (water shouldn't be there!).

As a personal example I once added sand to fiberglass resin to achieve a rough texture needed for this particular application. The sand was ever so slightly damp. The resin without sand dried quickly and without event, the resin with sand in took several days to fully harden.

When the chemical reaction between the catalyst and fiberglass resin takes place heat is produced, depending on the thickness of the resin the temperatures can get quite hot. Enough to melt plastic in extreme cases.

End result
The results which can be achieved with fiberglass are quite impressive. Its properties allow anyone to make an exotic bodyshell for a car. Once fully hardened and sealed with resin or a gelcoat fiberglass is waterproof, relatively light weight and when done properly it is extremely strong. It is reasonably inexpensive when compared to the alternatives, in short it is an ideal material for the automotive field.

What is Carbon fiber?

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