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Car Audio - Fiberglass Basics
Do you really need to use fiberglass?
Working with fiberglass is a very messy and time consuming process:
Prepare area, lay fiberglass, wait for it to dry, sand/cut if necessary, lay more
fiberglass, wait, sand, an so on. Once you are done with fiberglass, repeat the
process with Bondo (car body filler) for finishing: Apply, wait, sand, reapply,
wait, sand. It might take several days, even weeks to do a nice set of kick panels,
subwoofer box or amplifier rack.
If possible, try to determine if you can use an alternate material
such as wood and then shape using Bondo. Keep in mind that fiberglass is
strong when bent. Straight fiberglass panels have to be very thick (read: time and
money) for adequate rigidity. Sometimes a combination of wood, MDF or particleboard
(for large flat sections) and fiberglass (for round, odd sections) works best.
- Fiberglass mat or cloth, resin and hardener.
- Bondo (body filler), hardener.
- Box of disposable gloves, respirator, protective clothing.
- Paint brush, plastic sheeting, aluminum foil, mold release or WD40.
- Tools such as sander, multi-purpose shears, screws, etc.
For small projects, such as small amplifier racks or small kick
pods, you can buy all the supplies at a car parts store such as Trak Auto. Products
can be found at the "body repair" aisle. For bigger projects, supplies can
get pretty expensive. Boat supply stores sell products in larger quantities, but at
lower overall prices.
Fumes and dust particles are a very important concern when working
with fiberglass. Get a respirator or a dust mask designed to work with fiberglass.
Wear gloves at all times when handling fiberglass and resin, or sanding.
Protect ALL exposed skin, especially when sanding.
Work in an open area! Resin/hardener mixture fumes are bad for
your health. If you work with resin indoors, the smell will remain in the area for
days. Do not handle fiberglass mat or sand dry fiberglass indoors. It causes
rashes and itching.
Read instructions and warning labels carefully.
Before any work starts with fiberglass, plan the whole project.
Look ahead into how you are mounting speakers, components, fastening the panels,
panel finish, etc.
Once resin falls on carpet, upholstery, or other parts in your car,
there is no way to get it out. Cover areas to be worked thoroughly. If
possible, remove panels, seats, carpeting, etc in case an accident does occur.
Cover area to be molded with fiberglass with aluminum foil.
Fiberglass can be laid over the foil and once it dries, foil can be easily peeled off.
Making a Mold
If you are creating a shape in "mid air", you need to make
a mold first. There are different options available. Some people like to make
a frame out of aluminum foil and/or chicken wire. Other people use modeling clay or
shape dried spray expanding foam.
Another option is to make a "skeleton", shape it with
cloth and then fiberglass over it: Make a top and bottom part out of fiberglass,
wood, plastic, existing car panels, etc. Join both with wood or metal braces.
To fill the gaps, glue or staple sweatshirt material or pantyhose. Apply resin to
the cloth or pantyhose. Once they dry, lay fiberglass over it.
The third option is to use an existing shape, such as a spare tire
hole in a trunk. After removing factory panels and carpeting, apply mold release,
aluminum foil or WD-40 to surface (to avoid fiberglass from sticking). Lay
fiberglass, and let dry.
First, mix resin and hardener. Only mix what you will need.
It takes a lot of practice to get the resin/hardener ratio right. Too much
hardener and it will dry right away, too little and it could take several hours.
Temperature in work area also influences drying time. The hotter the
temperature is, the quicker resin will dry. Also, keep in mind that resin will get
warn when drying.
Cut fiberglass mat to size. It is better to cut a bigger size
than what you need for the first layer. You can always trim excess off when dry.
There are two ways to "wet" the fiberglass mat: By
dipping it in the resin/hardener mixture, or by applying resin with a brush. In most
cases, it is easier to dip the mat.
Once you have a wet mat on your hands, place it on the area that
will "shape it". If you are a beginner, this might be a bit tricky.
The mat will tend to stick to gloves and other stuff you don't want it to. Spraying
some WD-40 on your gloves will help a bit solving this problem. This first layer
would become the foundation of the piece you are building.
Once the first layer is dry, remove it from the car. In most
cases there is no need to work inside the car for subsequent layers.
Cut and sand excess fiberglass from fist layer, clean dust.
Add next layers in same fashion as fist layer. Try not to have any gaps or bubbles
between layers. You can use a cheap 1" brush to help get rid of bubbles.
Do not worry about imperfections at this stage, you just want a rough shape with no major
protrusions. All gaps and imperfections will be fixed at the last stage.
Shape and use of the object will determine amount of layers
required. For kick panels, 3 to 4 layers is usually enough. Subwoofers boxes
require more layers.
Once you have a defined shape, no major holes and a pretty sturdy
piece, you need to smooth out by sanding rough edges.
Bondo is very similar to fiberglass. Just add a few drops of
hardener and drying process begins. Spread Bondo over you panel. Try to fill
in gaps and valleys. Do not worry about smoothing it out much. Once
Bondo dries, sand. Repeat the process as many times as necessary: Add Bondo,
let dry, sand.
On the first steps, a power sander can be used to quickly remove
excess material. On finishing stages, manual sanding might be required, depending on
Finish smoothness depends on what material you are using to cover
the piece up. Carpet is very forgiving when it comes to imperfections. Vinyl
is less forgiving, you need a pretty smooth surface (a couple extra steps of Bondo might
be required). If you are finishing with paint, then you do need a perfectly smooth