I mixed some up as per the instructions and filled in all the cracks between foam pieces on the first level. I also did a little shaping to blend things in.
You mix the dry material with water that produces something with the consistency of lumpy porridge - assuming I've mixed it correctly. I applied it with my fingers, and sometimes used a small Tamiya paint mixing spatula for getting it into difficult crevices.
The instructions say it needs 24 hours to dry and harden, so hopefully tomorrow it'll be ready for some sanding and shaping. I'll likely need to apply a second round. If this works out I think this will be the material for building the mountain on the Elizabeth Valley layout. Stay tuned.