I drew out the profile of a horse's head on some scrap 2" thick Precision Board and then cut it out using a jigsaw. This was then screwed and glued to the sign face. Sculpting could then begin. Sarah mixed up the Abracadabra Sculpting Epoxy while I did the sculpting. To build up the shape I first pressed on a thin layer of sculpting epoxy and then use it to glue on balled up tinfoil. It is easily shaped. Another thin layer of sculpt was applied and more balls of tinfoil until I had the rough shape clearly defined. I thin applied one more layer of sculpting epoxy into which I sculpted the detail.
As added insurance that the horse's head stays on the sign I also put in a bunch of 2" long screws into the sign at various angles. Then I sculpted the epoxy for the horse's mane over them. This makes it impossible for the head to pull away unless the sign is broken up badly, not likely with the crews going into three plus inches of 30 lb foam.
Here's a closeup of the solid epoxy sculpted around the screws.
Now we are on to paint. Stay tuned...