Modeling fixer/spray on shell

Not even sure what to call it.

I'll give a specific example of what I need.  I'm building a rock.  It is a scenic element for an upcoming show.  It has to be large enough to seat two people, but light enough for one person to carry it offstage between scenes.  I have the rocks built.  I basically carved them from extruded polystyrene (pink insulation panels) but they are covered with a mache' of burlap, canvas, and glue to make them look more rock-like and to prevent paint from sloughing off revealing pink foam underneath.

I need something I can spray (or brush) on that is a "fixer."  When I say fixer, I don't mean like hairspray to give it a little stiffness, I mean like you can stand on it.  I could mix up epoxy and coat the whole thing, but that gets expensive and messy fast. 

I'm thinking like the plasticky stuff they spray over chicken wire to make dioramas at the Zoo or in the "pacific ocean" display at an Aquarium.  Maybe an epoxy that is thin enough to spray.  Hard shell stuff.  In the future I want to get two part expanding foam so I can cast things like this, then I want to be able to spray [insert brilliant idea] over it to make it a hard, light, durable theater prop.

Does something like this exist?

if it was smaller I would say vacuum form some thin sheet plastic over it 

Fiberglass chopper gun would probably be too heavy.....

californiamilleghia said:

if it was smaller I would say vacuum form some thin sheet plastic over it 

Fiberglass chopper gun would probably be too heavy.....

I thought about a chopper gun, but I think for the low-ish volume I'd be doing it wouldn't be worth the setup/cleanup.  I can understand if you're laying boat hulls all day and shooting 25 tons a week.

And I would LOVE to have a vacu-former, but again... volume per cost might be prohibitive.

I thought of an example though... Ever see the foam car ramps?  They are cast from some high density foam and coated with something.  They are rock hard.  You can hit them with a hammer and not hurt them.  Like these below... rated for 6000 lbs and weigh 10 lbs each.

But are the ramp molds sprayed first  with the hard stuff ( 2 part epoxy ) and then "foamed"

or  what about  wet formed leather.......

No idea how the ramps are done.  The description says "space age foam" and "non skid polyurea coating"

Sounds to me like 16lb urethane foam sprayed with rhino liner.

Artresin makes a two-part, clear, almost water-thin two part epoxy for coating drawings and such. 

I've used it for casting without issues so thickkess isn't a problem.

You could probably put it in a spray gun and shoot it, takes 24 hours to cure.

It's about $50 per gallon.