Help With Fiberglass

[Charles Warwick]

Okay, so I've been following the various fiberglasss/composite construction threads around here (Monomer, 10000 Degrees & Marko Ursin) and have been trying to figure out how to do it.

As far as materials go here's what I've pieced together:
-10 oz fiberglass cloth
-Resin
-Epoxy
-1/2'' Foam core
-fiberglass tape
-hot knife or hot wire cutter

Can anyone tell me where I might acquire the materials, and what types/brands I should be looking for?

And then as far as construction techniques go I have a couple of questions I hope you guys can sort out for me!
Here's the (very generic) process as I understand it:
1. Cut foam to size
2. Coat fiberglass cloth in resin
3. Lay cloth down on both sides of foam
4. Connect glassed pieces of foam using epoxy
5. Put fiberglass tape over seams and once connected, use resin (or bondo?) to coat the whole thing
6. Repeat
-Or-
1. Cut foam to size
2. Glue all foam pieces together using epoxy
3. Coat fiberglass cloth with resin and then lay it down over the completed box
Or somewhere between those two examples

People refer to things being laminated or coated, what is the difference?

Is it easier to glass the foam sheets and then cut to size, or cut to size and then glass them?

If anyone is willing to elaborate any of these steps or explain how to use fiberglass or resin I'd greatly appreciate it! Thanks!

Charles

P.S. If possible I'd like to assemble an introduction to fiberglass by the end of this; this is for posterity so be generous!

[sine143]

I glassed the 4x8 sheets, then cut everything to size. You can even use a jig saw if you feel like it.

[Charles Warwick]

I glassed the 4x8 sheets, then cut everything to size.

What kind of epoxy did you use to glue the fiberglass to foam? Did you rough up the edge of the foam before gluing it to the fiberglass?

How did you connect the fiberglass at the seams?

For reference this is a cost analysis of a 2X10 Zack2944 did over at TB forums:
http://i51.photobucket.com/albums/f398/ ... alysis.jpg

Where do most people get their fiberglass supplies from?

What is the difference between fiberglass Mat and Fabric?

[sine143]

I used western marine epoxy, didnt rough the foam really. I used kind of a peg system (skewers actually) to line up the pieces, and it was just epoxy on the seam, followed by epoxy and fiberglass tape on either side of the seam. woo!

I had most of the stuff on hand cause my family repairs boats and surfboards a lot.

That cost analysist looooks about right unfortunately.

[Rick Lee]

The best place ($) for fiberglass is Thayercraft in North Carolina and the best place for resin is US Composite in Florida. Definitely the best prices and the quality of resin/fiberglass is excellent. Steve gets deals on cloth by buying overruns and seconds. With speaker cabinets there is no reason to buy name brand cloth or resin.

Since it's a mechanical bond to the foam it wouldn't hurt to rough up the foam a little bit before doing the layup. Make sure you pull the thin plastic film off the foam sheets before lightly hand sanding. Don't wet out the cloth first! Lay the cloth over the foam and wet it out in one step.

Don't use fiberglass mat. Mat is none woven (kinda like osb in a wood sense) and is great for boats and things where light weight isn't the primary consideration. Sandwich construction is best used with woven fiberglass cloth because you need strength in stress directions (like trying to pull something apart).

Since you've never done this, I suggest you practice on a small piece first. Maybe take a 1' square, fiberglass both sides and after each side has cured cut it in two. Then join one edge to the other piece using the tape and epoxy. That'll give you valuable experience before you jump in doing a whole cabinet. There's a lot of ways to do it- the important thing is to have integrity at the joints.

[Charles Warwick]

Don't wet out the cloth first! Lay the cloth over the foam and wet it out in one step.

So, just apply the resin right over the top of the cloth? I had read elsewhere that you put resin down first for some reason.

Since you've never done this, I suggest you practice on a small piece first. Maybe take a 1' square, fiberglass both sides and after each side has cured cut it in two. Then join one edge to the other piece using the tape and epoxy. That'll give you valuable experience before you jump in doing a whole cabinet. There's a lot of ways to do it- the important thing is to have integrity at the joints.

That sounds like an excellent idea.

I used kind of a peg system (skewers actually) to line up the pieces, and it was just epoxy on the seam, followed by epoxy and fiberglass tape on either side of the seam. woo!

So was it just the tape and dowel joints that held the two pieces in place while the epoxy set? No clamps or screws or anything?

So most people use the West System Brand Epoxy? Is that just the best stuff to use? Would you want the slow or fast hardener? is 9-12 minutes enough work time for the fast? If I were to fillet the inside corners as others I have seen done to help the cloth adhere without peeling, would it matter which kind of filler I use? http://www.uscomposites.com/westfillers.html

The best place ($) for fiberglass is Thayercraft in North Carolina and the best place for resin is US Composite in Florida. Definitely the best prices and the quality of resin/fiberglass is excellent. Steve gets deals on cloth by buying overruns and seconds. With speaker cabinets there is no reason to buy name brand cloth or resin.

So is something like this a good choice?: http://www.thayercraft.com/332.htm

Your help is quite...helpful

[Rick Lee]

So, just apply the resin right over the top of the cloth?

Yes. If you have cloth that wets out easily there's no reason to do it otherwise.

That sounds like an excellent idea.

When you practice, join the pieces together in an L shape (instead of T shape) so you can practice on an outside and inside joint.

So was it just the tape and dowel joints that held the two pieces in place while the epoxy set? No clamps or screws or anything?

Really, it can be any way you want to do it. The strength doesn't come the way it does with wood - the strength is in the skin. You want to make sure that the load is carried from one fiberglass skin to the next. In other words, attaching one piece of foam to another piece of foam isn't important- attaching the fiberglass from one piece to another IS important.

So most people use the West System Brand Epoxy? Is that just the best stuff to use? Would you want the slow or fast hardener? is 9-12 minutes enough work time for the fast? If I were to fillet the inside corners as others I have seen done to help the cloth adhere without peeling, would it matter which kind of filler I use? http://www.uscomposites.com/westfillers.html

West System is good if you like to spend more than you need to. The 635 thin epoxy is basically the generic brand and for the purpose of building a speaker cabinet is great. Don't use the fast hardener for large layups. Not only does is set up quickly it is also more brittle when cured. Do you have a temperature controlled shop with a heat source other than non-vented gas heat? If so you'll be okay using slow hardener- much more forgiving time wise and you don't have to deal with amine blush. If the outside temp is still fairly warm up in Iowa the medium hardener might work okay for you. You definitely need to fillet the inside corners. Just use cabosil. http://www.uscomposites.com/fillers.html

So is something like this a good choice?:

The heavier the cloth the heavier your cab is going to be. Also the heavier the cloth the less dent resistant the cab is going to be so it's your choice which way to go. You want a cloth that wets out easily and conforms well. Give Steve a call and tell him what you're doing and he'll set you up with the right stuff.

[sine143]

haha, you guys were a lot more more informative than me.

I used west cause its what was on hand, and I dont even know what cloth I used (think it was 10 oz).

I didnt really clamp, but I may have just used weighted things.