Here is how it will lok at this point.
The scrap from shaping.
If you are happy with your wall, it's time to start epoxying the foam. I found the open pore structure of the foam will absorbed a large amount of the epoxy and that 2 coats worked much better in the end.
I used Acid / Epoxy brushes to brush on the epoxy. If you go to a hobby/craft shop, they are known as Epoxy Brushes, if you go to a hardware store, look in the plumbing section for Acid Brushes. They are tin handle brushes and cost about 25 cents. I used about 10 of them for my project.
Put a good coat on the front of the wall, making sure to coat all of the foam and about 1/6-1/4" of the edges of the rock, Let this dry, turn the panel over and coat the back.
Once that dries, recoat the front again, you will notice its easier to do now that the pores of the foam are filled from the first coat. Immediately pour your sand over the panel, I gently pushed it into the panel to assure good contact. Be sure to have plenty of sand, it is much easier if you have more than you need, what does'nt stick is still safe to use
Let it dry, turn it over and shake the sand off to be reused.
I first tried to use a sugar sand and the results were less than spectacular, it did'nt cover well, even after two coats.
Here is a pic of 3 panels. The middle is just epoxy, the left is sugar sand and the right is coarse sand. You can see why the fine sand does'nt work.
Here are the same panels all covered in coarse sand.
To mount the wall I used about 4-6 dimesized globs of silicone for eack 11"x24" panel. This is one of the reasons for coating the back with epoxy, I wanted a better bond than the silicone to foam. I was afraid of the foam tearing. This foam is extremely bouyant ans even with all of the rock, want to float.
One thing to note, as soon as I finished with applying the foam, I removed the trigger and tube from the can and soaked them in enamel reducer and cleaned the recess in the can using a twisted corner of a paper towel soaked in the reducer. I then attached a small piece to some thin wire to pull through the trigger and tube.
Doing this allowed me to reuse them both immediately, if you don't do this, you will have to let it cure and dig it out with a stiff wire.
I'm sure Laquer Thinner or Acetone would work also, probably even better.
If I missed anything, feel free to ask.