Fiberglass question

My friend and I are attempting to build a custom center console for a car out of fiberglass (which will eventually be padded and upholstered). The process we’ve attempted is as follows: build a mold out of styrofoam (we used styrofoam with large, white bubbles), cover it with saran wrap and vaseline, and lay the epoxy-soaked fiberglass mats on top. The saran wrap and vaseline is supposed to prevent the epoxy resin from dissolving the polystyrene, but it’s not working. The polystyrene dissolves, releasing gases which cause the end product to bubble.

My friend says he’s seen a video of someone making fiberglass molds out of an expanding foam: they pour the expanding foam mix into boxes to create a foam cube, carve it into shape, and apply the fiberglass: the resin doesn’t dissolve it.

We tested the type of expanding foam used to seal cracks in concrete, but it didn’t work. Having run out of ideas, we turn to the Dope:

How do people make molds for fiberglass? What kind of foam could my friend be referring to, or what should we use instead?

Polyurethane foam.

http://www.rqriley.com/frp-foam.htm

http://www.garbled.net/tim/fiberglass.html

Modern home-made aircraft are made with polyurethane foam carved to shape. If you want extra stiffness and light weight, you fiberglass right onto the foam. Use a plastc squeegee to ensure there is no extra resin and the cloth is nice and flat; two layers hsould do it. For extra stiffness, you build it out of thin sheets and fiberglass the inside too.

Google fiberglass airplane construction techniques and you’ll see lessons on how to lay up, resin, squeegee, etc. The result is a wing where (I saw someone do this) you can run up onto the wing, hop over the body of the craft, and run down the other side without denting the structure. Try that with a sheet aluminum construct.

Plastic can occasionally be useful. Vaseline: never.

Lets start with your styrofoam. No problem as long as you use epoxy, not polyester, the normal “fiberglassing resin” which will disolve styrofoam. You shouldn’t need to apply a barrier if you use epoxy unless you want to easily remove the foam later. Something doesn’t add up with your OP.

Secondly, you mentioned fiberglass mat. There’s 3 kinds of glass fabric, mat, woven roving and cloth. Mat involves a binder chemical that will not dissolve in epoxy so mat and epoxy is a no no. As I’ve never challenged this knowledge I do no have a clear idea if that is the cause of your problem.

The smartest approach is to get a** two part** polyurethane pour foam, lets say a two liter kit, mix it up and pour it into a box. Shape the resulting foam and apply your fiberglass directly over it with the much cheaper polyester resin.

The best solution is to buy some PVA mold release and spray or paint it on, it always works thats why pros always use it.

Just a tip. Nothing dissolves it. Once it’s cured, polyurethane foam is indestructible, except by things like mechanical cutting/abrasion and burning - there is no solvent. That means if you get it on your clothes, you will not get it off. If you get it on your skin, you have to wait for it to flake off as your skin exfoliates naturally.

Never attempt anything without the gloves.

True. I’ve had plenty of experience with polyurethane pour foams, but once I tried to make a shape with one of those urethane foaming cans and experienced something similar to the OP’s styrofoam, albeit with polyester resin.

Polyester gets quite hot while it cures, doesn’t it? (more so than epoxy, in general, I mean). Maybe the heat caused the foam to collapse or something?

The OP is not looking to separate the mold from the fiberglass shell he is constructing.

If you are intending to provide a barrier to avoid dissolving the foam, forget it as well. PVA works quite well on a smooth mold surface, preferably pre waxed and with several sprayed coats, however to use it on such a porous surface as foam renders it virtually impossible to ensure a complete barrier. One little entry point will initiate the destruction of the suspect foam.

Both polyester and epoxy (laminating type, not paint) have exothermic reactions, which are quite noticeable in the left over mixed can with a mass that can build up the heat.

In the case of the spray can urethane, its simply not the same reliable chemical that the two part polyurethane pour foam is.

To be clear.

With styrofoam, you can only use epoxy resin.

With polyurethane foam you can use both resins, polyester and epoxy.

Thanks to everybody for the great answers, as you can see we are rank amateurs here. The resin we were using is 3m bondo brand ‘proprietary resin’. The fiberglass is also bondo brand ‘fiberglass mat’. Beyond what it says on the packaging, that’s all I know about the terminology.

From what I gather from the replies, we have two options; we can use real epoxy resin (I had no idea there were multiple types) and we can make a new mold from polyurethane foam. What kinds of shops carry the two part foam, or epoxy resin in sufficient quantities?

Thanks again for the help!

Not sure about the foam, but boatbuilding suppliers and marine chandlers are often a good choice for the resin - epoxy is a very popular choice for boatbuilders of all kinds.