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Fiberglass in hatch

8548 Views 29 Replies 5 Participants Last post by  GarryGraves
Over the past few months, I've tried about 6 times to build myself some fiberglass enclosures to sit on both sides of the cubbies in the hatch. Needless to say I failed each time, and the serious lack of information on the subject coupled with frustration has led me to almost give up all hope of ever getting the huge box out of my hatch while keeping my bass. So what I need from y'all is one of three things:

1. A dumbed down walk trough to working with fiberglass
2. Somebody to build the molds themselves for me
3. Approval to use the existing plastic panel as the base of the mold itself

Any info or help would be greatly appreciated, this is the home stretch to finishing my interior once and for all.
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Garry, have a look in this photobucket album of mine.
Hatch Enclosure Photos by gstoddard | Photobucket

It is a pictorial documentation that covers when I built a sub enclosure into the rear hatch door. Different spot but similar process.

Do not use the plastic as part of the enclosure. Fiberglass does not bond to plastic worth a **** and it is not strong enough to hold up to the pressures a sub enclosure produces. You can use it as a mold to build the base off of, like I did using tape in the hatch door.

What problems are you having specifically. I've done this for years(10+) so I've got a little knowledge on it.
As said above, you have to use mat. The resin is just to bond the mat fiber to each other. Resin by itself will just crack and shatter as you have discovered. The tutorials that zinger posted are good ones to read. One thing to keep in mind when making the base mold is that it needs to be able to come out. You don't want sections that will get stuck as you are trying to pull it out of the car. If needed block those sections off so that the mold will release easily.
Alright now I finally getting the info I've been needing. 1 final question though, how do I apply the mat? Do I apply the wet resin onto the masking tape and throw the mat on it, then resin mat resin mat til it's thick enough?
Exactly! For any large flat areas just use 3/4" MDF, it's quicker and stronger than fiberglass and you can bond the fiberglass to it easily.

Keep in mind is you want as little resin as possible, just enough to wet out the mat. The strength in fiber glassing is all in the mat, the more resin you have the weaker and more brittle it becomes. Also if it is hot when you do it, mix small batches of resin and use less catalyst than recommended so that the resin doesn't harden up too quickly on you. I generally use 8 oz. of resin at a time.
Follow question for you Greg (since you seem to know what you're talking about):

I am trying to figure out the best way to fasten an enclosure to the car. I've seen a few places recommend industrial strength velcro. I'm worried that may not be strong enough. I don't want it to become a deadly projectile in an accident. I know the factory (Bazooka) sub installation calls for cutting a hole in the plastic to gain access to a nut welded to the inside of the quarter panel. Do you think it would work to put a piece of mdf on the back where the nut is and glass it in, then drill a hole in the mdf to bolt it down? I'm guessing I should use a rubber washer on the bolt head to seal it since I want a sealed enclosure.
That should work fine. I'm a big fan of bolting enclosures to the car, you'd be amazed at what can come flying loose in an accident. I'm not clear on where you are wanting to glass the mdf to though. That would be my only concern as fiberglass doesn't bold to metal or plastic well at all. And definitely yes on the rubber washer.
OK, that makes sense now. Yes, what you are thinking of doing will work great and give you a solid mount to the car.
Rule of thumb is that when built the enclosure should not flex when pushed hard with your thumb. :)

Generally if it is 1/4" thick it should be strong enough. I would say 4 layers is not thick enough, but it depends on what weight mat you are using. I generally use 1.5 oz. mat and build up at least 6 layers, if not 8-10. Also remember that fiberglass is stronger in curved area than it is in flat areas.

Do not drill a hole as this will change the characteristics of the enclosure and also you will get whistling as air is forced through the small hole.
Alright so update: over the past few days I've managed to add 2 more layers of resin and mat each, then mounted the speaker ring in the right side enclosure and covered it with fleece and 2 coats of resin. I wanna do 3 more coats of resin on top of that and add in the mat inside around the ring and the sticks to reinforce those as well. Tomorrow I'll be doing a testfit and a dry run with it to make sure its going to be stable, then its just a matter of making it look nice and securing it well enough. I can't quite thank you guys enough for all the help you all have been, especially Greg, you're my hero bro hahaha!

Just make sure you actually mat and resin the whole structure, especially the fleece. Fleece and resin is not strong enough to withstand the forces of a subwoofer. The fleece is just for shape it still has to be glassed just like the base for the same strength levels. Once the fleece is completely soaked and sturdy you can go ahead and remove the sticks completely, they were only there to get the ring positioned, you don't need them in there any more.
Why not just mat and resin the ring scaffolding into place? A little extra framework is well worth it.
There's is nothing wrong with leaving the framework in there but it does take up airspace and if the rest of the enclosure is build to strength the braces aren't needed. If it was large parallel flat areas then yes, absolutely you want bracing in there. With curved fiberglass surfaces they are very strong and sturdy, the bracing become redundant.
I keep having a scene in my mind where everything's hooked up, then the sub just blows the enclosure apart.
Just remember to record the first time you start it up, I want to see it explode. >:D

Actually wait until you get to the sanding stage, it's tedious, mind numbing work.
I was going to say looking at the picture that you should do a few layers where the fleece meets the mold from the inside. With that sharp of a transition you are bound to have leaks, but I guess you found that out. Yes, it would be a good idea to do the same on the backside of the ring to fleece transition as well. And yes it is a pain to do it but it gives you a double layer at a easy failure point. The learning curve for glassing is pretty steep but once you get there it gets a lot easier.
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