What kind of foam for diorama rocks/cliffs?

ManiacMotorsports Monday, 6/17/2024


I've been working on a private track for some time now, and it has cliffs (as most road courses do). I was wondering, what kind of foam do you track builders out there use to carve rocks out of? Spray foam or foam board? Also, painting the rocks to look realistic.




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redlinederby 6/17/24
Site manager

Building and painting are two separate things, right...but for building, I've been a fan of the solid pink foam stuff you get at Home Depot and the likes. Or even left over blocks of standard issue white styrofoam. I think it's easier to carve and shape than the spray foam. BUT, I think the spray foam lends itself to some interesting shapes that maybe don't even require carving.

For painting, I've just used good old acrylic paint and done my best. Nothing fancy there.

  • Yes. I've seen both of these kinds and considered them. Thanks! — ManiacMotorsports
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dr_dodge 6/17/24

I use mostly pink foam now, but some of my previous scenery projects used styrofoam, 

like the big chunks that are in boxes for packing

if you wash it w/ soap and water it gets the mold release off of the surfaces, and glues better

first coat is 50/50  elmers school glue/paint, of the "dominate" color

the next coat I use 50/50 wood glue/paint (helps it resist moisture)

and while it's wet, I dust it with colored sand, and fine ground foam scenery stuff


matte hairspray can be used as a final coat, and whenever the trees and shrubs look dusty


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CanesBart 6/17/24

Pink/blue the best, very hard to get.  Use a foam cutter, and get as dense a white foam as you can, look for 6 or 8 inch thick at construction sites (ask first, or wear khaki,  a short sleeve light blue button shirt, and a US Presidential seal cap, carry a clipboard, and....nevermind, just ask nicely for scraps)

  • Lol! — Dutch_Clutch_Racing
  • I worked at general dynamics in the '80s. You could goof off anytime by walking around with a clip board — dr_dodge
  • It’s the rule of ABCS - Always Be Carrying Something — AbbyNormal
  • lol — dr_dodge
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Chris_Hood 6/17/24


I found this video to be very illuminating on the topic. 100% with the comments above

(They actually build stuff; I'm just a fan)

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redlinederby 6/17/24
Site manager

Follow-up...with a post I made showing how I did scenery for my slot car track several years ago. It was literally trash piled up and then covered with the glue+paper towl combo, then painted. It worked very well and looks pretty good IMO. I didn't have to purchase anything extra, just used what I had.


I've seen a few tracks, skip the foam and used RAM board, or rolls of brown paper, if you crumple it before applying it, it gives a very realistic Brown Rock appearance. It would probably be easily and spray painted. 

  • Some RAM board product may be too thick to crumple however the red rosin paper and thinner brown underlayment paper are bang-on suggestions. The think RAM product, cut into strips, should make for some sturdy frame material in places! — Chris_Hood
  • I've seen that on a number of tracks. Thanks! — ManiacMotorsports
  • I use the brown paper. Amazon is always very nice and sends me lots for free when my wife orders stuff. — JBlotner42
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Chaos_Canyon 6/18/24

I've used a mix of insulation foam panels and spray foam. The spray foam is great if you're trying to make some odd shapes but if you cut into it, shows the air holes in the foam. The insulation foam is great and easy to work with but is trickier to get large build up areas as you have to layer it all. I stay away from normal polystyrene usually, mostly due to the level of mess with it and trying to clean it up is worse than the other two options.

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SpyDude 6/21/24

Model railroader here. When I did a couple of layouts, I used foam boards cut and stacked whatever way I needed it, then glued all the pieces together. You can create tunnels, mountains, roadbed, whatever you need with little effort. I've also used yardsticks as bridge roadway supports, vinyl tape for roads, and coffee stir sticks for fences, sidewall, docks and deck material.

  • Thanks! I used some tape as roads on part of my track . I'm planning to use GTR's tip that he told me. He used grout for the roads on Shavano Mountain Raceway. — ManiacMotorsports
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dr_dodge 6/26/24

Just did a week build 
painted paper to a decent start to a scene
as spy dude said, use any materials, industrial paper mache, gravel, ground leaves,
the best grey fine road gravel/ballast, go out to the road with a broom and dustpan (ignore the weird looks from the neighbors)
use a frypan screen to get the fine stuff, and grade up with bigger screen
and real dirt makes great scale dirt (who'd have thunk that...lol)

any questions ask away



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LordSyosset 6/26/24

I prefer the insulation pink foam board. Here is my announcer's booth using it with acrylic paint. Thunder Mesa Studio is a huge inspiration along with Black Magic Craft and Wylock's Armory, this guy is a wizard with just cardboard. I am also building my city and other buildings with coffee sticks etc. Great Ideas.

  • I have a whole collection of plastic stir stick, and my daughter worked at starbucks, and I bought a case of the wood ones, and use all of it — dr_dodge
  • very nice work! — dr_dodge
  • also, love the palm trees — dr_dodge
  • I like that. Thanks you! — ManiacMotorsports
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