I wanted to create a coral prop to use for our summer camp...so I came up with this method using spray foam.
Step 1: Spray Time
Okay, so I laid out some newspaper big enough to hold the entire size of the coral that I planned to make. I did draw it out, but ended up just making my own pattern in the end. I cut a piece of foam for the base so that it had something to help it stand up with and secured it in place with whatever I had laying around. Next I got a can of spray foam and started spraying out random strips of coral and then connecting the lines with criss cross shapes and patterns. Then let that dry completely.
After it's dry, you'll have to peel off the newspaper off the back (this is a pain), but it's the only way I could think to do it for this project. The foam sticks to everything when it is wet...so be aware of that.
Step 2: Paint It!
After it's dry and all the newspaper is peeled off, you can stand it up and start spraying it with any color of spray paint you want. I chose pink and used a purple to spray the underside of each section just to add depth to the piece.
That's it! It's a very easy way to create 3d coral that looks really cool in person and people will wonder how you got the coral so huge and lifelike right there in front of them. :)
Hope that helps you!