I have just a bit of experience with fiberglass, both polyester and epoxy. Yes you can use cardboard and wood as templates. Depending on complexity, you will need to also build molds. If you keep your shapes simple, you can seal the templates and then glass over them. Once the fiberglass cures, you can remove it and do final finishing. Try to maximize your support locations to minimize the fiberglass thickness required. You can also consider foam cores to minimize weight. I can assist more once you have a better idea of how you will proceed.

 

I have very limited fiberglass/composite experience but when working with larger pieces like an underpanel would be, I have found that a wood frame and foam is easiest for me to work with.

 

Alumalite might be a good choice too.

 

For a one off design I dont think you need to make a mold. If you just make your diffuser out of cardboard and apply resin and fiberglass directly to that, it would work right? If you want to reproduce it multiple times then you need a mold...

 

Race proven technology, anyone that tells you other wise is just spouting off at the mouth on a forum. They sell them where ever you can buy C4 ground effects kits.

 

Went under the Vette yesterday to have a look around. It looks like there are a few holes I can use so I dont have to drill into my car (I do not want to make new holes).

I took some measurements and came up with two questions:

1.) Can you mock up a diffuser out of carboard then epoxy and fiberglass over the cardboard (so the cardboard is part of the structure)?

2.) Where is a good place to get cheap cardboard and fiberglass stuff?

 

1.) Yes. But if any cardboard is exposed and water gets to it, it will rot. Make sure the epoxy is compatable with your resin. You might just use resin first on the card board itself before you start laying up your mat, let it soak into the card board so it becomes part of the structure. Ive seen people use a soft absorbant wood (pine, balsa) as thier structure, and layed up felt, fleece, cotton sheets and of course CSM (chopped stranded mat) or twill weave.

3.) Dumpsters for cardboard. Go behind pet stores... they usually have large boxes.
For fiberglass stuff, its pricey at parts stores, walmart and hardware stores. The best is to order it from one source, by the gallon of 5 gallon. Watch some videos online on how to fiberglass, how to mix resin, and what types of resin or materials to use. Make sure you get the right hardner for your resin. (the VOC on this stuff for MKEP is really stinky and can kill braincells. Please be aware of the personl safety required when using it!)
Boat stores usually have a selection of fiberglass supply, and some body shops might too.
For the finishing, I use regular body filler. I usually sand to 600-800 grit, prime then paint. Use compatible primer and paints.


An alternate to fiberglassing and wet layup is to from a shape with cardboard as a template, keeping it as straight as possible, then using aluminum, stainless sheet or pre-made sheets of carbon fiber to remake based off your template. That way you are just gluing them together or riveting them together instead of making an entire large peice of fiberglass.

When working with the glass and resin, you have about 15 mins before it starts setting up once the hardener has been mixed in. If its your first time, you may get caught half way done with what you are doing and it starts to solidify and get hot. This is frustrating. Especially if its a one off peice that would have to be remade if it was messed up. I encourage you to watch several videos of how others and professionals do it, it will save you!

 

AWESOME INFO!!!

The first step for me will be a mock up... I will look behind petco and petsmart to see if I can find some large cardboard pieces.

As for fiberglassing, I will definitely look up more videos and post one or two up here to get feedback!

How rigid can cardboard get if it is epoxied (with no fiberglass)?

If it takes 15min for it to start getting hard, how do you suggest doing a large area? Can you still add fiberglass after it starts getting hard? Can you fiberglass one side of the diffuser, let it dry, then do the other side?

Thanks!

 

PS. I am going to make a diffusser from the cats back (not covering the cats due to heat)...

Any concerns with exhaust heat and the fiberglass? Can I use heat tape or something to protect the diffusser?

 

It can get as stiff as the resin cures.
When fiberglassing, the fiberglass itself is flexible. The resin cures and could be compared to glue. What happens with you mix the two is the fiberglass gives solidity to the cured resin. Think mud straw hut... if it were made from mud, it would crumble. If it were made from straw it would be flexible and fall apart. Now put straw in your mud, and you now have a more solid structure hut that wont crumble like plain mud or straw.
the type of weave used in the glass, or the angle and length of the strands in CSM determins the strength of a composite. Things like fleece, cotton sheets, felt and cardboard arent going to offer the best strength when it comes to a layup. But they do provide great moulding capabilities, flexibility in design and they dont itch.
The resin carries the properties of flex, stiffness, toughness and more. Some resins are UV protectant, some are actually epoxies, and some allow a peice to be flexed to a certain point before snapping. Some are ment only for fiberglass or carbon fiber.

The point, the resin determins how stiff the structure is. The material beneath or imersed in it determins the strength (resistance to breaking). So the resin will be just as stiff on cardboard as on fiberglass, but it will not be anywhere close to the strength of fiberglass mat. (but you could use BOTH)


For a large area, it is best to have everything pre-cut. Have all of your layers worked out first, before you even open the resin. Once you have everything layed out and ready to begin, you mix your resin well, and follow the patterns youve layed out and it should be easy to lay down 5 or 6 layers before it starts to congele. You can presoak cardboard with the resin, and as the hardener sets up and catalyzes it should spread into your cardboard. you could also just resin up the card board with hardner first, and let it start to set up. then wither put layers on immediately or start laying up after the first layer has started to get hard. Once the reaction starts, you cant really slow it down. But after about 45 mins, the layers will get stiff but not be 100% cured. You can add more layers as long as the resin hasnt cured completely. If it did cure, any layers you add may not bond well and may seperate later.
You could do the other side later. But just know the layer in between is going to be the weakest.

Another little bit of info to look into is vacuum bagging. The industrial version of this is called an autoclave. This is where you use pressure to push out the excess resin and air bubles. This works really good. Might want to look that up too.

As far as heat near or touching the fiberglass... that would be bad. It will weaken the composite (composite is the result of fiberglass mixed with resin and cured). You could try to shield it, or insulate it. But remember, the heat needs a place to go! I would suggest using metal around any parts that will have heat on them.
Fiberglass in itself isnt flamable. The resin uncured is. Cured resin isnt any more flamable than plastic... But it would be wise to treat it like plastic when concerned with heat.

 

Thanks for all of the great info!

Which weight and type of fiberglass mat do you suggest and how many layers do you need to use in order to get a plywood type stiffness?

I dont know how to approach the exhaust heat problem yet...

 

1 1/2 oz./ft. CSM, layer with 18 oz./yd. Woven Roving. I say 7-11 layers with the bottom CSM and the top Woven. Id vacuum bag it to ensure there were no air between the layers and to get it as strong and even as possible.
Consider your gelcoat too...

 

I am a poor college kid so no vacuum bagging for me. I am trying to keep this as cheap as possible...

 

Lol, me too.

$1-$10 a dust buster from a thrift store
Free(all over campus): trash bags
Free: a tshirt
$3 double sided tape

you dont need to spend alot of money to make a vacuum bagging system. A shop vac would probably work better, but use what you can get your hands on.

 

I just purchased another ZR-1 yesterday that has a pretty good looking diffuser. I've never really cared one way or the either for a diffuser but I like this one. When I get the car home, I'll post better pics of it.

 

details on that car are here http://forums.corvetteforum.com/1571388665-post24.html

 

Thanks for posting better pics.

 

If you use poly-vinyl-alcohol PVA mold release, you can lay the matt on a flat surface (aluminum sheet) and then saturate the matt with resin. Use the cheap white bristle wooden handle paint brushes 2". When it hardens, just remove it from the surface and it will be smooth on one side.

 

^ He's got the right idea!

Ok, I used the term dust buster as in a general cheap vacuum... an actual Dust Buster wouldnt suck off an ant. But the idea is the same, you need to suck out the air and keep the layup compressed to get a good layup

 

Hey guys. Started making my mold this weekend. I'll get some pics up as soon as I can. Pretty pumped.

-Will