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
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
- Paint brush, plastic sheeting, aluminum foil, mold
release or WD40.
- Tools such as sander, multi-purpose shears, screws,
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
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
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
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 desired.
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