Styrofoam Rocks

Step 1 : Materials
I used the blue Styrofoam (DOW) that I picked up at my local Lowes. Here in South Carolina all I could find was 3/4″ sheet. Later on I found thicker pink foam (Owens Corning) at a Home Depot. I like the blue foam as it tends to ‘fracture’ in a rock-like way. I haven’t tried the pink stuff but it appears to be similar. There is a green foam you can get but it has more of a fiber-like structure to me .. I used it for stratified rockwork in another project.

Here I have some scrap Styrofoam and plywood which I will use to demonstrate my method. Note that I will deliberately glue the different layers of foam to create a stepped set of layers/strata .. making use of the 3/4″ thickness of the foam. You can hide the joints with spackle .. but much rock is layered so why not make use of it?

Step 2 : Stack and Glue
Glue the Styrofoam sheets together. If you live in colder climes you can find thicker sheets then the 3/4″ I used. Like I said, I didn’t have the pink Styrofoam others use available locally, so I can only talk about the blue stuff. I used ‘Liquid Nails Foam & Panel Adhesive”. Make sure you use an adhesive that specifically works with foam as many will melt it.

Read the label as some foam specific adhesives will only work foam to wood .. and not foam to foam. Go figure.

Step 3 : Implements of Destruction
These ‘steps’ .. are in no order what-so-ever and the tools are up to you from knives to your fingers. Whatever works.

I used a pocket knife to gouge the foam. Stick the blade in and pry up. Foam will fracture and pop out leaving random texture. I like the pocket knife as the blade is nice and sturdy and this process isn’t exactly delicate work.

Notice how the foam is fracturing. When you stick the knife blade in and pry up .. it ‘pops’ or fractures .. making a very nice ‘rocky’ texture.
Use your thumb and fingers. Pry, claw, scratch, twist, poke, prod .. whatever.
The foam cuts easily. Use the knife to cut .. but continue to create texture even while cutting .. slice in and twist the blade. You want it to fracture and not so much cut cleanly.
I had a sheet-rock saw handy. Fine. Sliced off a corner. Yea .. nice rough texture there!
Took the saw and dragged it down and across the surface to rip and tear.
How about another ledge? Easy .. just slice away.


Styrofoam Rocks — 6 Comments

  1. Great article! Nice to know you don’t need fancy tools. I have been considering using foam and your tutorial has convinced me it is the way to go.

  2. I’ve been doing this method for years. It it cheap, if you do a bit of curb shopping, easy; although a bit messsy, and fast. When I was first told about it I didn’t believe the individual how fast he had carved out his rocks. It is great and thanks for letting others know about it

    • Doug. Yep. I’m not going to claim that it is perfect for every instance .. *good* rock molds are hard to beat but for ease and quickly landscaping it is hard to beat.

  3. Ed, you made the right choice. …
    Here in the HOT Southwest, we’re lucky to find one inch Blue Extruded Foam!
    Even THAT is only readily available in 24″X 8′ pieces – and will curved lap joints on the long ends!! 🙁
    I MISS living in Illinois! I had ANY choice of foam sheets, pink, blue, green, in 4’X 8′ sheets, up to FOUR inches thick!
    I SHOULD have stocked up…

    Anyway, your point about blue vs. pink….
    The blue is, IMHO, much better for the purposes of carving. The main reason for that is – the pink foam is designed to “breathe” a little better. It’s made for applications where you don’t want all the air trapped in a space. I wouldn’t call it ‘porous’, but it’s quite a bit less dense than Blue.

    Blue Foam is very dense! That’s likely why it “shatters” for you instead of merely tearing away.

    …… I was quite ignorant at first, and asked a lot of questions about ‘Why Blue and Pink? Is there a difference?’
    I hope my psychobabble helps some.

    • Ok. Like that explanation. So far here is what I have found/seen ..

      Blue – Dow – they used to carry it at my nearby Lowes. Just why they switched to another type may be to do with what you are saying ..the kind of insulation needed related to humidity perhaps and not just the heat and cold? Shrug

      Pink – they have that at a Home Depot in Columbia. Since that is a good 30 mi round trip I never tried that.

      Green – this is where it gets weird.
      Type one – this is what my Lowes stocks now. It is more fibrous than the blue stuff .. so it tears rather than ‘shattering’. I used it to make the rocks in other areas of the layout – makes for more of a stratified rock since as I said it ‘tears’
      Type two – a friend purchased this at another Lowes about 60 mi from me and it is more like a florist green foam .. very cellular like – just not soft like the florist foam.

      Point being that whatever foam you can get you will need to experiment to see what you can do with it

  4. I have no access to pink foam. 🙁
    The blue stuff has been serving me well, but I miss variety. According to everyone I’ve talked to, for structural integrity, like to use as a layout base, pink is the best. Because the blue is so dense, if you used it as a table, it would likely snap!
    The pink foam (2″ min.), has just enough flex, to make a viable replacement for wood. The advantage is, in more weather shifting regions, a foam base doesn’t shrink and expand – destroying your track!

    I don’t think I’ll even mess with the green stuff…
    Too many variables!

    I can’t see why Lowe’s in Arizona can’t simply get 4x8s from back east….

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