Carving styrofoam to look like stone, brick, or cinder block is super easy. Perfect for Halloween decorations or haunted houses. I would even go so far as to say my technique is almost fool-proof.
Foam selection is probably one of the only ways you could go wrong. It needs to be EPS (expanded polystyrene) foam. Most commonly found in white. The pink or blue extruded polystyrene will not work. So make sure you have the right stuff to start. In my example, I will be making a faux cinder block effect. I may show some other textures and patterns in the future on my website. If you want a bit more detail on the whole process, check out my build article as well.
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Step 1: Laying Out the Grout Lines
Traditional cinder blocks measure 8" tall and 16" wide. Make horizontal lines with a permanent marker 8" apart and vertical lines 16" apart. Stagger each row for the "brick style" pattern.
Step 2: Cutting the Grout Lines
There are several ways to do this. My favorite is the hot knife tool. I also showed a couple other ways to do it with a knife (K), router (R), and hot knife (HK). Each has their own sort of look now but they lose that uniqueness in later steps.
Step 3: Give It Some Texture
Using whatever method you prefer, cut some voids into the foam. Make it as varied as possible and try to move around all over the panel at random. Doing it like you would read a book from left to right and top to bottom can give it too much of a uniform or segmented look. So remember to work in random spots. Also try to mimic chipped out corners and blemishes. A wire brush does pretty well with this.
TIP TIME - don't worry about perfection at this point - the next step is what makes it come together
Step 4: Hot Stuff!
Using a heat gun melt the surface of the foam. Heat guns with auto-cool-down last a lot longer than the ones that don't. I have a complete list of the tools and materials used in the web article if this is a project you want to give a try.
I start with the grout lines. Melting them to the point of where they start looking like mortar. Remember you can always come back and heat it up more if it didn't add enough texture. So go easy until you get the hang of it.
After the grout lines are done move to the field of the blocks. I can't stress this enough, all you do is melt the foam! It looks like there is a ton of time and experience needed for the final result but there really isn't. And it is one of those oddly satisfying things to do. Seriously give it a try.
I should note - cutting foam with hot wire tools gives off smoke and gas that is less than healthy for you. Heating the foam with a heat gun gives off far less smell but do it outdoors and/or use proper breathing protection.
Step 5: Paint Your Way to a New You (or at Least Wall)
WATER BASED PAINT! Yes, you need to use water based paint. If it is not water based, chances are it will chemically melt the foam. Spraying the paint helps preserve the texture we got with the heat gun but rolling or brushing is possible. If you can, spray it.
A base coat of an earthy color always seems to work well for the cinder block look. If you really want to sell the effect, airbrush a slightly darker color into the grout lines and depressions and it really pops. Or in the case of the panel meeting the ground, a bit of green adds the look of mold or moss build up. Just get creative with it. You can add vines or ivy like I did in the tower I made for the musical Shrek.
Again, if this is something you want to try out, check out my website article for more information and a list of tools and material used in the project.
Thanks for checking it out!