Foam for filling & fiberglassing cavities/voids?

[TOTalon]

I want to fill and fiberglass over a cavity. The volume of the cavity is too much to just lay down multiple layers fiberglass cloth, that would take forever. Is there any kind of spray-on foam that I can fill the void with, shape to the contour I want and then fiberglass over it? I was thinking about that expandable foam that some people use to stiffen a chassis, but maybe some of the experts here know of something better.

 

[Mike1992]

I recently dug out some rust holes from in front of my rear tires, I had 3 holes, 1 was about 6" wide and 4" tall, with scraps of old metel here and there, after getting all the rust get out and off, I sealed with rustolium primer, then proceeded with fiberglass bondo, then after shaping and all that not so fun stuff, I used that textured bed liner spray stuff then some paint. ?Good /Bad?

 

[Defiant]

The expanding foam is what you want, but go easy with it. Get a feel for how much it'll expand, because it doesn't like to stop until it's done. Once it is, it's easy to shape with a surform file.

 

[dave99gst]

brand name "stuff" expanding foam. And yes, if you over do it it can expand to the point of bending metal.

 

[tbehling]

when i fiberglass over "stuff" the expanding foam shrunk when i put resin over top of it

 

[TOTalon]

Thanks for the advice. So I assume the expanding foam dries hard? Is it the same stuff they do house insluation with or a different kind? Can you give me a ballpark of how much shrinkage to expect when I put the fiberglass resin on it?

 

[Defiant]

I think glassing resin will dissolve it slightly. A layer of paint or other resist would prevent it.

 

[bOOstd GSX]

I was thinking about that expandable foam that some people use to stiffen a chassis.

What is this product called, I was trying to figure out ways I could stiffen it.