Thread: Starting Fiberglass sub box!

Originally Posted by pcmofo

1. The sub needs 1 cubic foot of volume. How much resin, hardner, and fiberglass mat do I need to create a box that volume with 7-9 layers?

my guess is probably 2 gallons

Originally Posted by pcmofo

2. When I start by laying the first layer to create a mold of the inside before taking it out to finish the rest of the box do I only do one layer or do I do more than 1?

you can do about 2 layers at a time. doesn't matter when you do it, so since you're gonna have to wait for it to dry anyways, may as well put two layers during the first layup

Originally Posted by pcmofo

3. After the shell thats molded to the inside is out of the car and I start strengthing it with additional layers do I do 7-9 layers then continue on or do I only do few then create the rest of the box with a few layers then add additional layers to the entire box?

i'm not sure what you're asking here, can you clarify?

Originally Posted by pcmofo

4. How many layers should I do at a time before I wait for the entire thing to dry and then continue adding layers?

i've had luck wiht 2 layers at a time

Originally Posted by pcmofo

5. Any other tips or tricks such as watching for air bubbles or what type of tape to use to protect the inside of my trunk or how to relise the fiberglass from the trunk etc

use foil over the tape, the foil will act as your release agent. try to use wood for any straight panels. fiberglass isn't strong on a flat area, it uses the geometry of the curves to give it more strength. after you have your negative (the part you built to fit your car. dont forget about speaker rings and fleece. to get nicer corners and dimension from that method, i made a 'cage' out of wood dowels and then stretched the fleece over that.

My first one didnt turn out like i wanted it to, but my wife likes it. Its her car so i left it. Its still not done i have to smooth it out and paint it but here are some pics. maybe it will help you out some more.
I plane on making one for my jeep as soon as i get my pc installed and running.

sorry to critique your work, but just to help out the new guy....

you want to try to get a pretty uniform cover with resin. see the dark spots? could mean that the fleece wanst saturated enough...light spots would mean that there are air pockets. (though i dont see any air pockets) you can always grind down the are pockets and just add another layer. on your sequential layers after the first one, tear the fiberglass matt instead of cuting it. this will allow you to blend it better with the other pieces of matt.

Please, you can critique all you want. That was my first shot at it and i want to learn more before i place one in my jeep.
I never thought about tearing it. i did have more air pockets than i wanted.

I did learn one thing. wear rubber gloves when working with this stuff.

Good idea with the dowels etc. for finishing the edges. to clarify my one question there. ...

I do 2 layers inside the car... pop out the half when its dry then continue to add a total of 7-9 layers 2 at a time to the inside of the piece untill complete and dry....

then I test fit and cut to size the molded shell that I have now created and position my MDF board ring with dowels and test the volume.

Then I stretch the material over the whole thing and do 7-9 layers on the top half creating a sealed box again doing 2 layers at a time checking for bubbles etc lettting each dry completly b4 starting the next

then once it is complete and I cut out the hole for the sub I can water test it for volume and leaks. THen drill holes for speaker wire and mounting. Install and seal everything up. o yeah and carpet somewhere inbetween there....

The whole thing will have to be all fiberglass as there is really no large strait areas to use wood on... I could put a pic of my trunk up but there are some pics of it in the link to my project log and it looks like everyone elses.

I just finished building a box for my Dodge Ram Quad cab. I have a 12" Image Dynamics sub on the passenger's side and on the driver's side I created a locking storage compartment which I coated with Herculiner bedliner. This is where I keep my ball hitch.

I just did the final install in the truck today. After I cranked it up, all I could do is sit there and giggle because it was insanely over the top. It played loud and crystal clear. It was just wild!

I recommend doing 2 layers of glass before you remove it from the vehicle. Use fiberglass mat not cloth. The mat is made up of strands and overall is a bit thicker than the cloth. Its also just a little stiffer. But since you're trying to build thickness, I prefer the mat over the cloth.

Don't rely on tape alone to cover your carpet. Put down some tinfoil over the tape. It will form to the shape and will prevent leakage onto your carpet. It doesn't like to come off very easy so you might spray the foil with some kind of release agent. It doesn't hurt to leave the foil on the bottom but being a perfectionist I cleaned mine off the final product. I used a wire brush in an air die grinder.

Your project will take 2 gallons of resin. Buy a bunch of extra hardner, you'll use it.

If you get bubbles between layers, take a power sander and sand through the bubble and open it up. This will leave a cavity. Then take and pull apart some mat so that you have a bunch of strands of fiberglass. I filled a half a coffee can with loose strands. Dribble some resin where you had the bubble, then take those loose strands and start dabbing them into place with a paint brush. You can completly fill that cavity from the bubble this way.

When working with glass dab don't brush in strokes. You can buy a dozen or so of those really cheap brushes with the wooden handles. You can either soak them in acetone between coats or do like I did and just throw it away and use a new brush for the next layer.

Buy yourself a box of latex rubber gloves like they use in the doctor's office. You know the kind...when you hear that "SNAP" and the doctor says, "turn around and bend over." Those are words every man hates! A box of those gloves are nice because I used a lot of them. Don't try using one heavy pair of dishwashing rubber gloves. Its nice to have the disposable lightweight latex gloves to just toss away between coats.

Use 3/4 MDF for the frame. Make sure you predrill any place where you intend to install a screw. MDF splits easy. You can use a white or yellow glue for gluing MDF.

A roto-zip with a circle cutting jig works well for cutting the hole for the sub.

Use a good quality respirator. If you smell fiberglass, the respirator isn't doing its job.

how much fiberglass mat will I need to do a 1x1x1 foot box with 7-9 layers?

also if I am using 2 gal of resin how much hardner do I need? does it come with it and then I buy extra? what do you guys estimate the total cost to be?

The resin comes with the hardner. Its tucked under the plastic cap which is snapped to the top of the gallon resin can. You'll see it when you pop the plastic cap off of the can. At least the stuff you get at Home Depot and the hardware store is packaged that way. The instructions tell how much hardner to use. But its one of those things where you will use way more hardener than necessary. Everyone tends to keep squirting because of fear of not using enough. So buy extra hardner.

I don't know how much fiberglass mat you might need. But you can always buy more than you expect to use and return what you don't use. Personally, I'd buy 4 packages to start with just to be safe.

Home Depot carries the mat and resin in their painting department. If you go in and ask someone where they have their fiberglass resin you'll be met with a blank stare. They have no clue -- even the people in the paint department don't know what it is or where on the shelf they keep it.