Fiberglassing (on a budget) 101

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Intro and Supplies
Design and Setting Up
Resin and Strength
Sanding and Finishing

Design and Setting Up:

In this tutorial, we have already gone through the decision process to choose what type of enclosure we would like, and what we want it to look like. This is a simple sealed enclosure with a fiberglass baffle.

Finished Fiberglass:

Starting Out:

First off, we have cut the panels for the base of the enclosure, glued and screwed the top, bottom, and sides together. This tutorial assumes you know how to do that. Here is where we are so far:

Click all pictures to enlarge.

Note the 'dowel rods' we are using here are nothing more than scraps of particleboard cut to length. You'll need to take the speaker ring and position it where you want it to go. Take note of about how far away from all four sides the ring is so you know about where to position the dowels. Position the dowels where they need to go and hot glue them into place. Note: this may take several attempts to get the ring exactly where you want it. It is more trial and error at this point than anything else if you did not take the time to measure out each dowel (Not many people go that route).

Got the ring in place? Good, now try to remove it. Don't take a sledge to it, just pull and push on it a bit, make sure it is good and secure. Remember that you are going to have fleece stapled to this ring pulling on it constantly, and it has to last until the resin dries completely. If you are unsure about the strength, squirt more hot glue around the dowel rods, or use more rods. The process takes a lot less time than having to re-do your enclosure because you didn't take the time to set it up properly.

Instead of buying dowel rods, use 1/2" or larger strips of scrap wood (mdf works great). If you do not have a staple gun for the fleece, use the hot glue gun, it takes a bit longer, but you don't have to buy a staple gun!

Now lay your fleece over the area to be covered (note: white fleece works better in our opinion, it is easier to see what are has been completely soaked in resin).

At this point, start stapling. You'll want to staple on the side of the ring, if you staple to the top, you will have much more sanding to do, as well as have to remove the staples for a nice clean look.   We generally start stapling the fleece to the ring first, and then stretch the fleece to everything else. It makes it easier to get it stapled to the ring. On this enclosure, we decided to go with a raised look, so we stapled the fleece at about half way down on the side of the ring.

If you staple the fleece right up to the edge of the box (shown below), you can trim off the excess and will have less sanding time in the near future.

Get Fiberglassing:

You are now ready to start fiberglassing. Put that shiny new organic respirator on. Get your mixing cup out and measure out the correct amount of resin and hardener. There are two methods to do this depending on where you get your resin. The first, and most used by DIY'ers is to count drops of hardener. Follow the directions on the can - so many drops per ounce of resin, and so on. The second is mixing by weight. Using a scale, you will measure out the resin you need and add (usually) 1-3% hardener. Again, follow the directions on the can. You'll want to mix the stuff for a good two-three minutes to get it completely mixed. *Important: Try to get as close as possible to the desired concentrate of hardener in the resin. Do not just guess. If you get too much hardener in there (mix it too 'hot'), your resin will dry too quickly, it could warp your part from the heat, or your part could even catch fire! If you mix too little hardener in the resin, you could let the part sit for a week and it will still feel tacky.

Instead of cleaning out your mixing cup every time, line it with plastic wrap or some kind of plastic material that will not break and is not very expensive so you can just take it out and throw it away each use.

Now, before the resin dries (you have anywhere from 5-10 minutes of working time before the resin starts to harden), you need to soak the fleece with resin. You can use a paint brush, plastic squeegee, even your fingers if you dare. DO NOT be afraid to do this in two stages. If you feel you need to mix much more resin to coat the fleece than you will be able to use before it dries, do it in multiple steps. You also may have to do a coat on the outside, then flip the thing over and do a coat on the inside.

The fleece will dry in an hour or two. (Note: You do not have to remove the dowel rods at this point. You do run the risk of warping the part due to heat from the resin curing if you do. If you take your time and lay one layer on at a time, this will most likely not happen. The choice is yours) Once it dries completely, you can carefully pry the dowel rods from the ring. Take care in removing them because the fleece may be hard but it is still brittle without any reinforcement - remember it only has resin on it, not fiberglass. You will then want to lay fiberglass on the inside of the panel. Always tear the mat into strips about the size you need. Mix the resin as you have done before and apply a thin coat to the back of the fleece. Once you have applied resin, lay the strips of fiberglass mat on  fleece, and apply more resin to the top of the strips. Make sure to "wet out", or 'coat completely', the strips of fiberglass mat, but do not over-apply the resin.

You can do two layers of fiberglass mat at a time if the part is not too large. On a larger project, try to only do one layer at a time. If you use two or more, the heat from the additional resin hardening could warp your part, causing you to start over. Wait until the resin is at least mostly dry (1-3 hours) to apply a new layer of mat and resin.

HOW THICK DOES IT NEED TO BE?

Ah, that is the question everyone asks themselves from time to time. Our answer? Thick enough to have adequate strength to jump on. Rough estimates? Remember that fiberglass is stronger when curved then when straight. Try to use MDF on straight planes when possible. On a small part like this box - try three layers of mat, and test it. On a larger part? Try five layers and test it. How do you test it? When the resin is dry, try pushing on the part to see if it flexes. Use your thumb and push hard against the largest area of fiberglass - does it flex? No? Ok, put it on the ground and stand on it. If there is no flexing, it should be OK. In general terms, if you would not feel comfortable jumping on your part - you should not feel comfortable putting a sub in it. If nothing else, a good rule of thumb is about 1/4" - 3/8" thick on a normal size enclosure.

Now, to be honest, most subs will not blow your box apart if it is not adequately reinforced. But it will have that "fiberglass" sound to it if it is not built properly. A main key to proper sound is to have adequate strength!

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