Fiberglass Step by Step

A step by step guide to creating with fiberglass

by: Drew Wilson

I am often asked where I learned to work with fiberglass, or where an individual can go for a good write-up in order to learn how to fiberglass. I've never had a good answer until now. I didn't "go" anywhere to learn other than the Internet and my garage, and I can't recommend any of the Internet sites I'm familiar with as each has distinct drawbacks. It seems that they are either corporate write-ups that are only out to promote their own expensive products, amateur write-ups that are thrown together and may have inaccuracies, or manufacturer's sites which simply show the steps taken in great detail without the necessary background (Alpine's site for example). I am in no position to discount any of those sources for information since they are basically all I have had in my personal fiberglassing education, but I hope to go beyond their usefulness to the every day weekend customizer. I plan to do so by bringing the information from those sites together with my experience and presenting the information as simply as possible. I will focus on keeping costs and the time involved down as much as possible, but the advantages of using fiberglass will always come with an added cost in both dollars and time when compared to  "cookie-cutter" MDF, and stock speaker location installations. Finally, although I have achieved some level of success and certainly a ton of experience for an "amateur" I attribute most of that to the amount of time I'm willing to spend redoing my own mistakes rather than to any talent or special knowledge. If you think you know a better way to do something you should, obviously, do it your way.

There are a few basic concepts in fiberglassing, which a thorough understanding of will allow you to create practically anything. What I mean is that the same basic skills that enable you to build a kick panel or a subwoofer enclosure can also be used to create a bumper. I've decided that the best way to present those underlying concepts and to help people with their projects is to go through a couple of ways to build shapes in fiberglass, then briefly present a third method. The idea is that the reader will be able to just follow the instructions to do most typical projects or to use the concepts in them as a springboard to creating virtually anything.



The materials you will be working with are the most important determinant of the outcome of a fiberglass project.  They are also a great place to save some money.  I'll not go into the normal tools such as an angle grinder or the wood saws that you'll be using, but I'll make sure to point out the specific materials needed

You will need to find a local distributor for fiberglass resin and mat.  This may be difficult for many of you due to geographical constraints, but if you're determined to find one you should be able.  I know it took me a year of using the inferior "Home Depot" branded resin, before I got off my butt and found a place locally to sell me the good stuff, mainly because I thought the good stuff would cost more.  The truth is that I save about 35% by purchasing from my local distributor in 5 gallon pails (5 gallons is too much for virtually any single project), but even if I weren't saving money it would save me a ton of time and improve the end quality of my work to use the good resin.  When you buy from Home Depot or Walmart or any of those places you get resin that is thicker, sets-up slower, and sets-up weaker than the better stuff out there (you'll know if you have the better stuff if it is at least as fluid as cooking oil, the bad stuff resembles molasses).   Try calling around to local audio shops or marinas until you find what you need.  It is also possible to mail order, but the cost seems prohibitive to me. Single gallons should be $25-30 and 5 gallon barrels should be around $100-$120 with the necessary hardener.

Buy "chop mat" from the same place you buy the resin.  I'm not going to go into the different weights of matting, but obviously the heavier weights are "stronger" and the lighter are easier to use (forcing a heavy mat over a curved surface without either cutting it up into tiny pieces or creating air bubbles can be an impossible challenge).  You won't need woven matting for most projects.  There is only one other thing I would recommend purchasing from your fiberglass supply store and that is a sprayable polyester body filler, or what Duratec calls their "base primer".  "Base primer" can either be sprayed through a primer gun or painted on with a brush and can be applied very thick.  It is easy to sand and when you plan on painting your finished product it allows you to jump ahead rapidly if you paint it on after initial sanding with 36 or 40 grit paper and then begin sanding it with 80 or 100 grit.  It is roughly $40-50 for a gallon, but if you build a large enclosure or a fiberglass rollpan using it might save you many hours.

Fleece is necessary for most projects.  I most often just use whatever fleece is cheapest at Walmart.  The fleece is basically only going to be used to provide an initial backbone which the mat will add strength to, don't fall into the trap of thinking that fleece and resin alone is rigid or durable enough for much of anything.  There are "special" fleece's available from a few sources that claim to be thinner, stronger, stretchier at a much greater cost, you will be able to make do with the cheap stuff and any time you could have saved with the specialty fleece will be more than made up for in savings. You are going to be looking at paying between $4 and $7 a yard for fleece.

The only other "specialty" material that is universally needed is body filler. You will need to use some body filler to smooth your fiberglass work even if you are going to cover the final product with vinyl, and the brunt of your work will be at this stage if you are trying to prep for paint. In keeping this simple, I will break body fillers into those that have some ground up fiberglass strands in them and are meant to be used to provide some strength and those that do not and are exclusively designed for "finishing" and "feathering". There are times when you want the body filler to "hide" your errors earlier in the project and you need to put it on somewhat thick. Whenever you need to add any thickness of filler use one of the products that provides strength (also note what you did wrong and correct it the next time- you don't want to ever be in that situation if you can help it). The "finishing" filler always follows the other or in cases where the shape is correct from the beginning it is all you would use. I personally use Duraglass and Rage Gold respectively.  I have found that it is distinctly not worth trying to save money by using inferior products when it comes to body filler. You should pay just less than $30 a gallon for either of those. Everything else you will need you either already have or probably wouldn't appreciate my advice in purchasing.


Basic Stand Alone Subwoofer Enclosure


Here are two examples (Thanks to my brother Ryan and friend Pierre):




 In order to build a box like this you start with an MDF frame. You can choose to make as many sides of the frame as you wish MDF. Here are a couple of shots of frames from my friend Pierre's Explorer's box and my brother's Escape's box -

The key is to get a feel for what your frame will look like once you have stretched fleece over it. At first you will likely end up with nothing close to what you were expecting for your final shape. Be certain that you take your time creating your frame because if it isn't square you will waste a ton of time making the final product square later. Make sure you plan out where any LCD screens, amplifer(s), ports etc. will be going at this stage and remember to think about where any wires will run. At times you have to be very creative in how wires will get from one place to another inside a box (ex. the wires going to the 13" screen in the Escape's box above).

Once you are happy with your frame you will drape the fleece over it making sure that you have plenty overhanging all sides. Start in the middle stapling the fleece to your frame stretching it hard and working outward in an even radial manner. You need to be certain that you start in the middle and stretch out in each direction from there evenly. Upon completion, place your work on a drop cloth, put on some latex gloves, and mix your resin. I recommend using a flexible Tupperware type bowl (approximately 40 oz size). With Tupperware after any unused resin hardens you can flex the bowl and crack the resin out so you can recycle the bowl for quite a while. Be sure to follow the directions for mixing the accurate amount of hardener. Finally, "paint" the resin onto the fleece. The tendency is to not apply enough resin and there is no real drawback to applying too much so be aggressive. After that stage your enclosure will look something like this-

That is my little brother Ryan's current box in his Escape. Hopefully, your garage will look a bit better. You'll have an hour or two to go watch TV or whatever while the resin hardens. When you come back use a Rotozip or something similar to cut out the holes where the subs go and any other holes that are supposed to be in the box. Use a flap wheel on a grinder to clean up the edges (the bottom edge above had a big lip on it where the resin and fleece had built up).

 At this stage the enclosure is flexible and weak. The mat is used to add strength. You are going to have to make a determination based on the size of the enclosure and the output of the subs you will be using how many layers of mat you will need, but it will be at least three and probably not more than ten. The size and shape of the pieces of mat you will use will be up to you in each situation. I would recommend starting with 4"x6" pieces." Paint" some resin onto the surface of the fleece, place the 4"x6" piece of mat on the fleece and then paint over the top of the mat to completely soak it with resin. Move quickly until the entire surface has been covered, slightly overlapping each neighboring piece of mat. Use whatever method of dabbing or brushing enables you to avoid air bubbles to the fullest extent. A trick to help avoid bubbles around curves and edges is to tear the mat rather than cut it with a scissor. The torn ends are much easier to force into a shape of your choosing. Take care around the edges where the fleece meets the MDF. The mat and resin will stick and seal to the MDF as well as they will to the fleece and you want to take full advantage of that fact to be certain the edges are sealed. Repeat this process as many times as is necessary in order to achieve the level of strength you need. With enough properly applied layers fiberglass can withstand incredible abuse.

 One way to possibly save yourself a lot of time is to apply the mat and resin to the non-cosmetic inner surface of your work. When you apply the mat on the side you are planning on eventually painting, no matter how carefully, it will result in you having to add some Duraglass in order to smooth out some high and low spots. If you can get away with leaving the bare hardened fleece on the cosmetic side you may only have to use the finishing body filler and can save a ton of time sanding. I did this with my current box in my explorer. It requires leaving one side of the box "open" so that you can reach in and apply the resin and mat like this-


In most situations doing it that way would have been more trouble than it was worth, you have to make the decision on the basis of each project.

Once you are comfortable with the number of layers you have applied and the strength of your enclosure it is time for body filler. You will have to use your own judgment in deciding with which type of body filler to start with. In the most extreme cases you will have to do multiple coats with Duraglass just to get the shape and curves under control. I like to sand the early coats with a 40 or 60 grit flap wheel on a grinder focusing on the general curves. Whether you are painting, or covering the enclosure with some sort of fabric you need to get it completely finished to the 36 or 40 grit sandpaper stage. Once again focus on the general shapes and curves being certain they are as you want them. When you are at that stage you could wrap the enclosure with vinyl or another fabric and call it quits. I may do an addendum later describing that procedure and the products I've found that are easiest to use to that end. If you are planning on painting the finished project you are now ready to apply the base primer if you have it. Brushing or spraying the base primer on will basically allow you to skip from 36 or 40 grit all the way to 80 or 100 grit sandpaper. Once you have used it I assure you that you will never go back to working your tail off applying coat after coat of "finishing" filler and sanding with 60 or 80 grit (but if you don't have base primer you'll have to do exactly that). Once you get to 100 grit you can use regular sand-able primer rather than body filler between bouts with the sandpaper. I don't do my own finish paint work, but in general I try to finish everything to 220 grit before turning it over to whoever is doing the painting.



You can use the same skills to create another type of enclosure with just a couple of changes in how you set-up the "frame". First here are two examples of "spare tire enclosures" that I've done recently-

That is a true example of a "spare tire enclosure" in that it uses that space and no other space at all. Those are pictures of my Audi A6 Avant. The following pictures of my friend Rhys' J-spec Toyota Supra also show an enclosure I would consider a "spare tire enclosure" although it has sort of grown out of that space a bit-

The key common denominator between those two enclosures is the need to use as much of the airspace available as was possible. The spare tires from both cars were removed in order to gain space leaving me with a very uneven surface that would have precluded any efforts to make an MDF frame that used all of the space available. The "frame" in this case actually becomes the car itself. With a few layers of aluminum foil and masking tape carefully protecting the surface you are "molding" or "framing" off of you can skip straight to adding mat in order to create a piece of fiberglass fit perfectly to the space available-

On the left is the Supra (I used fleece rather than mat in order to save as much mat as possible-I think we had purchased all the mat on Grand Cayman for our projects at that point and I was afraid of running out), and on the right is the Audi. You will notice the MDF ring that was placed around the top of the space I was molding in the A6.That ring gave me a base to build more MDF off in order to make the top of the enclosure. Here is an inside peak at the MDF framing that occurred in the Supra-

There was still more MDF added later in order to house the Memphis Belle amplifier (and its wiring) and the plexi window into the sub (which was finished on the inside with brushed aluminum) but that gives the general idea of what you are trying to do. Once you are at that stage in the process it is no different than making a "normal" fiberglass enclosure.



The third method of making a frame I often use is with foam. The advantage of foam is that you can literally cut or shape it by sanding to make any shape. That is how I made my bumper, side skirts, rollpan, grille, and hood on the Explorer.


I use the green foam available at most craft stores and Walmart which is primarily intended for making fake flower presentations. It is widely available in 2"x12"x36" pieces that can be glued together with liquid nails. I've seen Chip Foose using suspiciously similar looking foam in huge blocks, but I haven't yet figured out where to purchase those. The beauty of this foam is that you can cut it with a knife blade or sand it with 36/40 grit sanding paper into any shape you choose. Once you have made the desired shape in foam you can then either lay mat directly onto the foam (mix the resin a little cold or else as the resin's exothermic reaction takes place as it hardens the foam will literally melt away) or you can devise a way to wrap the foam with fleece. You can use liquid nails to attach the foam to just about anything, such as the bottom of the stock bumper or the side skirts to which you're trying to add some depth and shape.



I could go into a lot more detail about exactly how to do a lot of the details such as how the Audiocontrol EQX was sunk into the enclosure in my A6 or where the wires for that screen in the Escape do go. However, I think its better that each prospective hobbyist figures those types of things out on their own project by project. I know I hate just "copying" someone else's design or ideas. I don't know any other major techniques other than what I've presented here and I have been able to make a ton of other parts that I never would have though possible before I started working with fiberglass such as the dash in my Explorer.

Which reminds me how far behind I am with taking pictures (it does have a finished fiberglass center console too).

I hope that this gets people started in the right direction for their initial forays into working with fiberglass, and that it might provide some new ideas to people with experience. Anyone can feel free to email me on AOL instant messenger at wattsupcustoms or at with any questions or comments. I wish I had more complete pictures of the procedures outlined, and for that manner more completed projects.