Starting Fiberglass sub box!

**Shadow** · 10-04-2006, 01:16 PM

Baum, that was posted no less than 3 times. It's still good advice, but it's a reeeeeeeeeeeeeee.

**psychotic** · 10-15-2006, 11:17 PM

SOOOOO
I've been following this, and i'm thinkin about making a sealed box, and then putting a fiberglass design that goes over/around this box (probably with foam, but still...) and then covering it with a black vinyl material for a leather look.

ok... fiberglass resin, and hardner. is this like expoxy? must mix for it to activate?

when he refers to soaking things in apoxy to harden it, what is the "apoxy?" Does he mean the fiberglass resin/hardner combo?

fiberglass matte - fiberglass cloth - wool

for my application, (correct me if any part seems wrong, or an easier way) I think am going to use foam(suggestions on type?) and shape it around the mdf box, since the f/g itself isn't the box.

To reshape foam, I hear you need to prime it before using bondo, because it will eat away the foam?

So I glob it all up with plenty of bondo *(w/ the fibers, kitty hair or whatever) and shape it with, something like a putty knife and a grater, then sand smooth...

then, do I need f/g cloth, or just layers of resin on top of the bondo?? also, is there a way to mix coloring in with the resin to give color a deeper appearence in case I decide not to wrap them??

Then for the 6.5 speakers, I'll use the mdf circle and pull... wool?? right?... over it to form the curves and meet up with the foam before it has resin, apply resin, and then layer on my matte or cloth... does it matter? is starting with matte and then going to cloth a good idea?

for my aplication, I'd think a couple layers of matte, and then a couple layers of cloth will be good, especially since the speaker will be in its own box, and the only thing the f/g will be supporting is 6.5" coaxials on each side of the box.
This fiberglass is meant to cover the entire rear deck under my rear window in my 06 sentra SeR... the whole thing doesn't need to be fiberglassed, cause I can just pull vinyl over the flat surfaces, but still, most of it will be f/g... so I'll need to mess around before I go for the real thing. Give me some tips guys... this seems a little different considering i'm making a sealed box out of mdf and then fiberglassing...

The sub box will be bolted down to the metal frame on the back deck, and that is what will keep everything in place (hopefully)

**GoHybrid** · 10-16-2006, 01:02 AM

I would highly recommend against *globs* of bondo/kitty hair. just get your foam to exactly the shape that you want and then start laying chopped mat/resin over that. If you're using the foam as a male mold and calling it good, then you can use bondo as a SURFACING aid. i.e. filling tiny little pits and low spots.

But yeah, if you're using a styrene based foam, you need to put a barrier coat over it to prevent it from being attacked by the resin Use latex paint, not rattle-can primer or anything with solvents in it. The good news about this approach is that you can melt out the foam when you're done and have a fiberglass shell that you can put things in. An example of styrene based foam would be the pink or blue sheets of insulation you get at home depot, or a styrofoam cup.

One way of getting around a barrier coat is to simply use a resin that doesn't contain styrene monomer. This would be an epoxy resin. Epoxy resins tend to produce slightly stronger parts, don't smell as bad, and are pretty straightforward to work with. The benefit of polyester resin is that you can vary your working time with the amount of hardener you mix in. That way you don't have to worry so much about the environment you're working in.

Urethane foams are a different animal. Almost completely resistant to any chemicals, so unless you can separate your fiberglass part from the foam (by using appropriate mold release), it's pretty much captive. Urethane foam would be RenShape or Great Stuff types.

As for coloring, i wouldn't bother. You'll have to do so much levelling and sanding with these approaches that no color you mix in will look reasonable. Just prepare your surface, get it smooth, use a good primer and paint it if you want color.

Lastly, you can use all kinds of fabric to stretch over your speaker rings. It kind of depends on how delicate your touch is. Fleece is popular because it absorbs lots of resin and gives you a good quick starting place to start laying in your reinforcements. I don't like BECAUSE of it's appetite for resin. I tend to use much thinner fabrics with less surface texture. Takes a little bit softer touch to handle while reinforcing, but it saves some resin and finishing time. Thinner fabrics can also help in getting tighter corners. Experiment with a few types until you find your match.

**psychotic** · 10-16-2006, 01:20 AM

thanks for the tips. I think I'm going to cover it in black vinyl if possible... Also, I was originally planning on leaving the foam under the fiberglass, because some of the foam will be on the top of my sub box (so i can't really remove it....). In this case, what type of foam do I need to use to keep it from dissolving under the resin??? Also, where can I find such a type of foam (that can still be shaped)
Thanks

**GoHybrid** · 10-16-2006, 12:49 PM

well if you want to keep the foam, then you can use whatever you like. Just make sure that if you're using polyester resin with a styrene based foam that you give it a good solid coat of latex paint to shield it from the solvents.

Your other option (and the easier one in my opinion) is just to use an epoxy resin.

In any case, you can find EPS foam at home depot in big 2" thick pink boards.

If you really want to create a well defined shape, you can get a piece of RenShape 5025 from www.freemansupply.com

**psychotic** · 10-16-2006, 03:28 PM

Thanks,

I think i'll just stack and glue the foam from lowes or home depot to make my curve, at least for the top of the box. about the resin, is epoxy resin harder to find??? like is polyestey resin the main kind used?

**Naamanf** · 10-16-2006, 03:39 PM

Epoxy is harder to find but shouldn't be that difficult. The major drawback is the price. It's usually 2-3 times more expensive than polyester. Given the choice I would take epoxy except for the price. Money to burn, carbon fiber, or gel coat epoxy is the way to go. Just doing simple fiberglass work, polyester.

**psychotic** · 10-16-2006, 06:00 PM

good timing i just found different shapes of white styrofoam at walmart!
and while i was there i got some 50% polyester fabric to test it out on before i do the real thing... see if it melts before the resin hardens..?

**GoHybrid** · 10-16-2006, 07:51 PM

again,

styrofoam = styrene based foam
polyester resin = contains solvents, makes lots of heat during cure time.

solvents + heat + styrene base foam = puddle of toxic goo.

If you care at all about the integrity of your shape, you'll cover any exposed area of your foam with latex paint. You can probably pick up your favorite color of interior house paint from lowes for $5.

**psychotic** · 10-19-2006, 12:10 AM

I decided to mess around with it a bit before trying the real thing. I bought the regular elmer's resin in a can with hardner under the cap, not the exensive white stuff. I smeared a ball shapped piece of styrofoam from wal-mart with the resin/hardner combo. no puddle... if it is eating away, it is doing so at a pace that I already had pieces of fiberglass sheet on 4 hours later. Oh, and ya I tried following the instructions pretty good by guestimating my ammount of resin and adding the correct # of drops.... the stuff is still sticky after about 10 hours. eh. but ya, no melting styrofoam from this little test. Most chemical reactions that set up hard generate heat, but when working in smaller layers... maybe the heat isn't strong enough to just melt the styrofoam. i'll post a pic later of it with the 1st layer