Thanks everyone and Psyclone figured it out it is spray foam. It is fairly easy but i had used/experimented with it a few times before I made this. I was using it for something at work and instantly the light bulb popped up. So go get a can and experiment a little, watch how it expands, put different amounts on a few pieces of cardboard and watch it grow. It will grow until it is dry so start off sparingly until you have the idea. It dries Tan and I spray painted everything brown then gave it a series of tan washes to get the right look. The gate is simply foam core that was painted. I even have the gate key pad in the back room that Luke hits with the skull. If you guys are interested I have about 30 or so photos of every element of this scene...just like the movie.
