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· former owner
7,435 Posts
Discussion Starter · #1 ·
Fiberglass 101

Ran across this info while learning how to do this. It's a lot of reading, but it really helps to get us "do-it-yourself"-ers started.
You can cick the links below, or in case the websites get shut down or remove the pages, I also copied the info directly to the post.

->Fiberglass Basics<-


Blistering: A phenomenom which occurs in boat hulls because the materials used to manufacture the hulls is water permeable (generally FRP). The laminate absorbs moisture which collects on the surface, intermediately or deep. Eventually, the pressure from this water buildup is high enough to form bulges in the surface.
B-Stage: Intermediate stage of curing. Not yet fully cured. Will not flow, but will yield to pressure.

Cohesion: The state in which the particles of an adhesive are held together.

Composite: A combination of materials that result in an end product with characteristics superior to any one of the elements singly.

Core Materials: The central member of a sandwich construction. Normally low in density, light weight material used to separate structural skins. Typically weight is expressed in pounds per cubic foot.

Cure: The change from liquid to solid caused by chemical reaction of the components of an adhesive.

Fiber Content: The amount of fiber present in a composite.

Fiberglass: One of the oldest, strongest, and lowest cost reinforcement materials of all fibers today. Does not burn, shrink, stretch, or absorb moisture. The fibers are available in woven and non-woven forms.

Fiber Reinforced Plastic (FRP): A general term for a composite that is reinforced with cloth, mat, strands, or any other fiber form and resin.

Fillers: Materials which are added to resins or gel coats for special flow characteristics, to extend volume, or to add strength to the article being produced.

Hand Lay-up: Refers to prewetting mixed resin using a brush, roller, or squeegee. The fabric product is placed over or into the resin-wet open mold surface and resin is again applied as necessary to achieve a totally wet laminate. Successive laminates and or core materials are added into a designed schedule.

Heat Deflection Temperature (HDT): The temperature at which a material will begin to soften and deflect under load.

Laminate: Product built up by bonding two or more layers of materials.

Microballoons: Tiny hollow spheres made from various inert substances, i.e. glass. Mixed with resin, Microballoons increase the volume and make the cured resin easier to sand.

Primary Bonding: Bonding situation where laminate is completed in one continuous cycle without total curing of intermediate plies.Primary bonding is advantageous over secondary bonds as interlaminar properties are enhanced when a chemical as well as a mechanical bond is present. Sometimes the part size, thickness or manufacturing sequence preclude a continuous lay-up, thus requiring the application of wet plies over a previously cured laminate, known as secondary bonding.

Post Cure: Heatng solid during curng time to increase physical properties.

Pot Life: Amount of time between the mixing and gel stage in which an epoxy remains usable in the pot at 77oF. Pot Life for epoxies depends on temperature, shape of container, and hardener used. Pot Life is different from Working Time.

Print Throuqh: Teleqraphing of the image of glass strands throuqh the gel coat film. A visual phenomena caused by low Tg temperatures when air in entrapped in the glass fibers.

Secondary Bonding: The joining of two or more already cured composite parts using adhesives. The only chemical or thermal reaction occurring is the curng of the adhesive itself.

Strength: The measure of the stress required to deform or break a material.

Tg: The temperature at which a thermoset resin will begin to loose stiffness properties.

Thermosetting: A resin that polymerizes when subjected to heat. Epoxies are thermosetting.

Thin Film Set: The surface becomes tack free. A thumb print will show on the surface, but no epoxy will come off onto your thumb (Please wear gloves!)

Toughness: A measure of the energy required to break a material.

Viscosity: Thickness of a liquid. Honey is very viscous, water is not. Expressed in cengpoise (cps). The viscosity of water is 1 cps. Higher numbers represent thicker material.

Wet lay-up: This method is normally used for building fiberglass boats. Dry glass reinforcing mat, or cloth is laid out on the inside of the mold and covered with resin from a bucket or spray gun. A roller is then used to press the resin into the glass and to work out air bubbles.

Working Time: Length of time during which a formula remains workable after it has been applied.

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.


  1. Fiberglass mat or cloth, resin and hardener.
  2. Bondo (body filler), hardener.
  3. Box of disposable gloves, respirator, protective clothing.
  4. Paint brush, plastic sheeting, aluminum foil, mold release or WD40.
  5. 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.

Car Preparation

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 Layer

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.

Additional Layers

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.

Bondo Stage

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 surface.

· I Like Fire....HaHaHa
5,295 Posts
If you guys have heard me explain fiberglassing in the past and never understood where or how to get some of the supplies I've talked about such as Micro-Balloons, Epoxy, various weights on fiberglass sold by the foot rather than the cheap stuff Walmarts got thats all folded and creased up. I am providing a website and a series of links to all of these various supplies, to even include various desities of foam for sanding and shaping as a base for fiberglass in lue of an mdf skeleton and even the 1/8" thick plywood I've described previously too. Hell, you can even get plexiglass and a number of other materials for fabrication.

The company name is Wicks Aircraft Supply. There you can get so much stuff related to fabrication its really not funny and sort of overwelming at the number of stuff they have.

Lets not forget that aircraft have far more involved in terms of making them fly and look good in comparison to cars. Obviously this site won't have V8 engines or car related parts per-say but everything you could possible need for fabrication on some level, even metal and aluminum, can be found here:


Bellow are direct links to some of the key materials us mini-truckers might use that this aircraft supply site has.



Fiberglass (many weights available):

Epoxy and Resin Fillers (Micro-Balloons):

Fiberglass Reinforcing tape:

Making Molds:

Kevlar (Excellent for Woofer enclosures not using a full mdf skeleton. This shit after several layers is super freak'n strong. Lets not forget bullet-proof vests and composite armor are made with many layers of Kevlar):

Lexan plexiglass:

Lexan plexiglass Cutting Tools:

1/16", 3/32", 1/8", 3/16", 1/4" Plywood:

Metals (stainless, steel, aluminum, rod, angle, tube, sheet....what ever you need)

Tools (various depending on the function and purpose):

Hole Cutters for custom dash guages, door speakers, woofer enclosure....anything needing a hole:

I know your thoughts will be, "damn this place is expensive". I too agree but if you have no other means of getting the proper materials locally then this is a great option for you.

Also, some times doing an outstanding job on a project means taking your time and spending the extra money on the proper supplies for that project rather than coping out to the costs demons and use cheap ass supplies which consequently make it harder for you to turn out a decent product. These materials will make life easier.

My father builds airplanes like we build cars or trucks. His airplane was a show winner twice at Oshkosh EAA airshow in Wisconsin because he took his time and used supplies strictly from this company to get things done. Cause of the cost it took him 10 years (obviously cause its an airplane and needs far more shit from this site than you and I would) but being on the cover of 4 magazines with his plane made those 10 long years worth it.

Try the site and links out and feel free to pm fiberglassing questions when ever you need.
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