Composites 101: Carbon Fiber, Fiberglass, etc.
I thought this might be a good place to start a discussion about building with composite materials such as fiberglass, carbon fiber, and Kevlar.
Over the past year, I have done a bunch of research on the subject(s), and have hit some pitfalls along the way. I have also had some small successes through trial and error and some very useful stuff I have found on the web.
I was hoping to utilize the wealth of knowledge on this site to compile a roadmap for do-it-yourselfers who want to build with composites.
I will attempt to keep up-to-date on the posts here, and use page 1 as a repository of useful knowledge, with links, so one need not search through pages of the forum to find the information they seek.
Since I came into this thing with absolutely no background in working with composites, I will try and keep it simple for people like myself; a sort of Composites 101.
Disclaimer – most of the chemicals used in building with composites are dangerous as hell. If you blow yourself up, or cause yourself physical harm in any way, blame yourself for not using the proper safety equipment.
To begin, just some basic theory:
The idea behind building with composites is that you begin with very light material such as fiberglass, carbon fiber, or Kevlar. These materials are composed of fibers that are oriented in a way so that the sum of fibers is stronger than the individual fibers. The fibers are then arranged in sheets, and the sheets are layered atop one another to further increase strength.
The layers of composite sheets are held together by “glues”. These “glues” are generally referred to as resins.
Resins are thick/viscous liquids that are very sticky. As they dry, they become stickier. Eventually they harden – almost like sap from a tree. The most common resin for composite building is made from polyester.
Resins will harden over time, but the time to harden (or cure) can be decreased by the use of a catalyst. In the world of chemistry, catalysts make chemical reactions more energetically favorable. Think of it this way, many chemicals won’t react with other chemicals, because it takes too much energy to start the reaction. They are very lazy. Catalysts make it easier for two chemicals to begin a reaction. Once the reaction begins, heat generated from the reaction itself, will create energy that propagates the reaction.
In the case of polyester resins, the catalyst most commonly used is Methyl Ethyl Ketone Peroxide (MEKP).
Other factors that effect how quickly a resin will harden are temperature, humidity, and pressure. The higher the temperature and pressure, the quicker a resin will harden. The role of humidity is more variable, but in general, the more humid the air, the slower the process of hardening. Pike Bishop has added his experience with epoxies: the more humid the air, the faster the cure time.
The amount of catalyst can also effect cure time. With respect to polyester resins, increasing the volume of catalyst decreases the cure time. This is usually not desirable, because if the resin cures too quickly, it often compromises the strength of the resin, and therefore the composite. Adding too little catalyst may result in a product that never really hardens as it should.
Epoxy can also be used to glue the sheets together. The advantages to epoxies are they are much less caustic and much less dangerous. Unlike polyester resin, epoxy does not dissolve plastics and Styrofoam. When making plugs and molds, it is often desirable to not dissolve everything. Like polyester resins, epoxy requires a catalyst. In the case of epoxy, it is usually called the hardener.
The disadvantages to epoxies are that they are much more expensive, and they weaken when exposed to ultraviolet radiation. There are UV-resistant epoxies available, but the price is even higher for these.
Some great links about epoxies provided by Pike Bishop: West System User Guide Epoxyworks free online magazine
Now a word about some common materials needed:
Fiberglass comes in a variety of weaves and thickness. I haven’t spent much time working with fiberglass, so I will limit my discussion to saying that the least expensive way to build with composites is to use fiberglass and polyester resin. I have no experience in how to build a strong fiberglass piece that is cosmetically appealing.
Carbon fiber comes in a variety of thicknesses and weaves. The more complicated the part you are making, the thinner you will want the sheet, so that it will lay over bends and contours. Carbon fiber is significantly more costly than fiberglass. The adage that carbon fiber is stronger than steel, yet lighter than aluminum is true, but it really only applies to carbon fiber pieces that are created in a very specific way (requires the application of vacuum, heat, and pressure). The stuff that one can build in a garage will likely not have these optimal characteristics.
It is possible to purchase sheets of carbon fiber that are already impregnated with resin. However, this practice is generally limited to aerospace and Formula-1 race teams who have serious cash resources to purchase (and store) impregnated carbon fiber.
Hybrid cloths combine Kevlar and carbon fiber into a weave. The really cool thing about these fibers is that they come in a variety of colors, yet retain characteristics of carbon fiber. However, a word of warning: once the resin is added to the hybrid, the color changes significantly. Think of it this way – if you spill water an your cotton T-shirt, the wet spot has a distinctly different color than the dry spot. The same happens with these hybrids; the color may be spot-on when dry, but once resin is added, the color changes, and the cured product is a different color than the dry cloth. Kevlar is very good at dissipating energy - hence its use in bulletproof vests. Kevlar can be combined with Carbon Fiber, or even fiberglass to make a cloth, but can also be purchased as pure Kevlar. Kevlar does not resist UV-light very well. Kevlar, and thus its hybrids are generally more expensive than carbon fiber.
Polyvinyl alcohol (PVA) is a blue liquid. It is essentially like liquid Saran Wrap. Applied in liquid form to molds or plugs, once it dries, it forms a micro-thin barrier that will prevent resins, epoxies, and gel-coat from sticking. It is easy to find, and pretty inexpensive.
Gel Coat is essentially a polyester resin that has been thickened and pigmented; and therefore comes in a variety of colors. Gel coat is what gives fiberglass parts that super shiny smooth appearance (think of a fiberglass boat hull). Since Gel Coat is made from polyester, it retains similar characteristics; UV-protection, tends to melt plastics and Styrofoam, and requires MEKP as catalyst. Gel coat is a very good material for making molds because when it cures, it is super smooth and sandable. There are different types of gelcoat, and they are generally quite expensive ($60-$100/gallon). Gel Coats will clot up if they sit around unused for long periods of time, so when you buy it, make sure it has been made up recently, or the seller is willing to guarantee the Gel Coat will be free from clots. Tooling Gel Coat is designed for mold-making. It is supposed to be harder and tolerate the rigors of multiple pulls from one mold. I have had no luck whatsoever with tooling gel coat. It is more expensive than regular gel coat, and it tends to crack when it dries. I have given up using it entirely.
If you are committed to using gel coat(s), I have personally had much more consistent results using it when the ambient temperature is 70 degrees or less. When it is hot outside, even though I am in an air-conditioned environment, my results have not been as consistent as when it's winter outside, and I am running the heater in my shop. That being said, since I started making molds with epoxy, I doubt I will ever use gelcoat again.
Mold Release Wax is essentially just wax like you would use to wax your car. Other than being heat-resistant, I don’t know what other properties it contains. A can of mold release wax will cost about the same amount as a can of good car wax.
Vacuum bagging is a whole other process and is discussed here.
The first build:
At a minimum, I think one needs the following items to create a carbon fiber part:
1. Carbon Fiber
2. Polyester Resin
3. MEKP – usually comes with the polyester resin - do not be fooled into buying methyl ethyl ketone at Home Depot - it is not the same stuff
4. At your local Home Depot you can get a good pair of scissors
5. A well-ventilated area, or a respirator
6. Latex or nitrile gloves
7. Some cheap paint brushes (chip brushes)
8. Disposable paper measuring cups that are not lined with wax, or disposable plastic measuring cups (but if the resin and catalyst are left in plastic for more than an hour, it will dissolve the plastic) - if you are using epoxy, you can use Styrofoam cups
9. A syringe for measuring MEKP (can be obtained from a corner pharmacy)
10. Polyvinyl alcohol (PVA)
Where does one go to get all this sh*t? I recommend Jamestown Distributing. They have a large variety of products, they are good about offering free shipping coupons, and they ship quickly. Other places I have purchase from include Elite Motoring on Ebay, USComposites, and Fiberglass Supply.
Another excellent resource is YouTube. There are some great instructional videos on how to fabricate with CF. I highly recommend watching as many of these videos as possible before starting your first project. 3 hours on Youtube can save you 3 hundred dollars, and 3 months in the garage. Jamestown Distributors also has a repository of awesome instructional videos.
CF parts can be made in a variety of ways. One of the simplest things to do is just layer CF over a part that is already made. Okay, so this is not really a part made of CF, but it does have a nice look.
Essentially, all you need to do is buff the plastic so it has a rough appearance, paint on a layer of epoxy with hardener, put on a layer of CF, then repeat. Once you have 2-3 layers on and it is dry, add one to two more layers of epoxy with hardener to give it a nice gleam. The final product will still have a somewhat rough appearance, and it will not retain the most desirable characteristics of plastic or CF…it just looks cool.
The next thing one can do is to create a mold from a piece of Styrofoam. Then using epoxy, layer CF atop the Styrofoam. Once the CF is cured, Acetone can be poured on the Styrofoam, and it will dissolve without dissolving the CF and epoxy. Here is another link to building atop Styrofoam.
This is a piece I made with Foam Core Posterboard. It took me just a couple days to whip this out:
The strongest and most ascetically pleasing pieces are also the most labor and time-consuming, and will cost a bit more to make. This process involves building a plug, then a mold, then using the mold to create your piece…
This is a piece I made recently. This is the piece freshly pulled from the mold. This is before sanding and finishing, and already it has a beautiful appearance.
Get some books on composite boat building. There is all sorts of info on vacuum bagging in your garage.
Looking good! I played around with making a few flat panels several years ago. How did you keep the weave from distorting around the curves on that last piece? Uscomposites.com was where I purchased my supplies from. "competition car composites" (a book) gave me a bit of unconfizzling as to the process.
So where to begin? I wanted to add a rally-type fairing to my bike. To begin with , I used foam board that can be found at any crafts store, or even your local Wal Mart. Using a razor blade and tape, I made the design of my plug.
The foam board plug was then covered in Bondo, and sanded into the desired shape. I use 4-5 coats of Bondo to increase the strength, and the thicker Bondo allows me to sand down hard edges. The picture below shows hard edges on my mold - I paid for this later as my plug was destroyed as I pulled it from the mold.
I have since found that the best way to do this is to use some wood glue, and glue the foam board plug to a piece of plywood.
By gluing the plug to plywood, the Bondo can be flared onto the vertical portions of the plug, and the plywood makes pulling the plug from the mold easier in later steps. I have found that it is best to leave about 3-4 inches of space between the edge of the plug, and the border of the plywood.
By far, making the plug is the most critical step when making a really good composite part. A good plug yields a good mold, which gives a good piece. The plug should be as free from blemishes as possible. Some other pitfalls to avoid:
1. The demarcation between the plug and the plywood is the hardest area to keep free of blemishes. For that reason, when I make the plug from foam core, I extend the perimeter of the plug by 1-2 inches all the way around. In that way, the blemishes on the final product will be on excess areas, and can just be cut away
2. The plug cannot have angles more acute than 90-degrees relative to the bottom. The lower parts of the plug, the parts closest to the plywood, should always be wider than the top parts of the plug. The reason for this becomes obvious when you make your mold. It only takes getting a plug stuck in a mold once before this concept is solidified in your brain.
3. The edges of the plug should be rounded off. Sharp edges and carbon fiber don't mix.
Now that you have the basic shape of your plug, it needs to be as smooth as possible. In the past, I have spent hours with sandpaper, starting with 40 grit, working my way to 800 grit, to make the Bondo as smooth as a baby's bottom. This is incredibly time-consuming, but effective.
I have recently found a much more efficient way of doing this. Now I just sand it down to 100 grit, then I cover the plug with West System's Epoxy:
Although West System's epoxy resin and hardener represent a significant expense. I have found that they save lots of money and time in the long run. The cost of a gallon of resin ($82), 1 quart of hardener ($36), and the resin/hardener "300 mini-pumps" ($12) is significant. However, once I realized I could save hours of sanding by using epoxy, I would pay twice as much if needed.
Anyway, once the Bondo-ed plug is sanded, I cover it in a couple of coats of epoxy. I just use a cheap chip-brush to brush on the epoxy. The plug in the picture needed about 400 mL (13 ounces) of resin to do 2 coats .
When dry, the resin is super smooth, and fills most of the major blemishes in the plug. Trust me on this one, I have spent DAYS sanding a plug, and I will never do it again. Covering with epoxy is quicker, easier, and the final plug is smoother and stronger.
The epoxy has a tendency to create tiny little bubbles when it dries. A blow dryer or heat gun can be used to pop the bubbles before they dry, but there will always be some left. They leave tiny imperfections in the plug that need to be sanded away. 100-grit sanding, followed by 600 or 800-grit wet sanding is all it takes to smooth out these tiny bubbles.
Any big holes or blemishes in the plug can be corrected with Loctite's Epoxy Glue . I just put a dab on the blemish, and use my finger to wipe it away.
This is the plug after 2 coats of epoxy, then about 20 minutes of sanding with an electric hand sander; 100-grit, then 600-grit wet sanding:
The next step is waxing. I usually put on 3-4 coats of mold release wax. The wax will fill any tiny holes, and further smooths the plug. This is just like waxing a car Daniel-son, Wax on, let it dry, Wax off.
The next step is the PVA. I found the best way to apply this is with an HVLP paint gun and air compressor. I have tried applying the PVA with paper shop towels, and with cans of compressed air, but the best results have come from using the paint gun.
I mix the PVA with 10-20% water, then I spray 3-4 coats of PVA over the plug, allowing time between coats to dry. In the dry heat, and under a West-Texas sun, the diluted PVA dries within 10 minutes. After the third coat, the HVLP gun is cleaned out by running copious amounts of water through the gun (about a gallon). After one coat:
After 4 coats:
The PVA has run in some places, but those won't be on the final part, so I let them be.
Once I have a few layers of PVA on, I build a box from plywood.
The box sits around the plug:
There is always a small gap between the plywood the plug sits upon, and the plywood box.
I just add some Super Duper Fabricating Material (duct tape) to the outside to prevent epoxy from seeping through the gap.
Next step is to layer coats of Epoxy and hardener atop the plug. After the first coat (about 300 mL).
I will use 3-4 coats of epoxy, allowing it to dry to a tack (when you touch the epoxy, it's a bit sticky, and your fingerprint remains) between coats.
The last step of making the mold/plug involves adding 1-2 layers of fiberglass and resin to strengthen the mold.
The more pulls you plan to do, the stronger you will want the mold, and therefore the thicker will needs be your epoxy layers and fiberglass layers:
In a West Texas summer, I will let this cure overnight before attempting the pull. If it is winter, I will let these cure for 3-4 days before attempting the pull.
Next step - pulling the plug from the mold...This is where you find out if all your hard work, time, and money have paid off. Scary!
After letting it cure overnight, I pulled the plug from the mold:
The green patina atop the mold is the PVA. I will wash this off with water and a soft kitchen sponge.
Here is the plug after the pull:
It is in the same condition it was before making the mold, so it can be used in the future, if I want to alter the plug and/or make another mold.
Allow me a few lines to say that using West System's epoxy is by far the fastest, easiest, least labor-intensive, and least expensive way of making the plug and mold. Again, it represents a larger initial investment than Gelcoat and Polyester Resin, but I literally have wasted hundreds of dollars and hundreds of hours of time working out the nuances of gelcoat - and I still don't have a single perfect mold to show for it. I have a bunch of shoddy molds that have needed repair and a dumpster full of failed molds and plugs. Also, the investment into an HVLP paint gun will save money in the long run, because it makes pulling plugs and pieces SO much easier and effective. If you already have the air compressor, the HVLP gun is a small investment compared to time and supplies saved. One last thing is the vacuum pump. Vacuum bagging is not necessary, but if you want a really light, strong part that looks really good, you need to vacuum bag.
I will relate my experience: Trying to save money, I used polyester resins and polyester gelcoat. It spent months building plugs, sanding them to perfection, applying wax, then PVA with a cloth, then making molds from Gelcoat. Without fail, when I have pulled the plugs from the molds, either my plug or my mold has been irrevocably destroyed each time. This destruction means lots of time and money lost.
The last two plugs and molds I made using West Systems Epoxy and the HVLP gun as described in the steps above. The last plug and mold I made took me about 10 hours total from start to finish. Quite literally it has cost me a fraction of the time, and a fraction of the money, and both my plug and mold are intact.
Vacuum bagging represents another large investment, but again will save time and money, and yields a better product. I will speak more on vacuum bagging later.
Great job! I'm looking at doing some CF for my ST2 Project bike so am keenly watching.
Excellent write up!! I have worked in fiberglass for a dozen years. Your 101 information is spot on and full of good info.
If anyone is in So. Illinois or St. Louis area I would be happy to sell you any of my chemicals/ fillers/ etc. at cost. G.P. resin $20 gal.
Great info - thanks for taking the time to write it up.
i have a vintage fiberglass skidplate i'd like to reproduce in cf. i've laid up fiberglass before, but not cf. i'm assuming they are pretty similar, wth cf just being more critical to looks when laying it up. dimensions are not critical for this skidplate.. i'm assuming i can slap some mold release on the original plate, and lay it up? also, how many layers and what kinda resin/hardener for an EFFECTIVE skid plate ?? how can i stop edges from fraying - i've had cf pipe guards that frayed the edges relatively rapidly.. also where can i get inexpensive cf (3k?) about 12"-16" wide. cosmetics are not so important....durability is.
defender.com is a good source for FG cloth, kevlar and other composite reinforcing materials.
"Epoxy Works" is a free magazine (also online) produced by the Gougeons of West System epoxy; it's a really good resource and well worth checking out.
I've done a fair bit of marine FG work.
The time-consuming part will be sanding the original skidplate so it is smooth as can be, before adding the wax and/or PVA. When you begin, I would have the resin without catalyst already measured out, with pre-measured catalyst ready to go. Also have all your CF pieces cut and ready to go. Once you add the catalyst and hardener, you're working against the clock.
Once it is cured and ready to cut, I use my Dremel and a diamond-tipped cutting wheel, to prevent frayed edges.
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