|My "mountain" is just about complete. 28mm and 20mm figures for scale.|
I'll give you a brief overview of how I did it. The original idea came as I was helping my cousin cut up his old hot tub. Inside the tub was this yellow foam insulation that we took out in large pieces. I took those and stored them and after cleaning them up I cut and sanded the bottoms so they would lay flat leaving the rough, bumpy top surface. I did sand down a few sections to give me some flat areas and also cut a few spots for layering my "rocks". I primed the entire piece with some green spray paint and once dry started to glue my rock pieces in place using a hot glue gun. The rocks by the way are just pieces of rough cut pine bark mulch that I bought in a 40lb. bag at Home Depot. I sorted pieces by shape and allowed them to dry out before gluing them in place. I then started layering the bark pieces on top of each other to form my basic bolder structure. Once the piece was all glued, I started dry brushing a variety of grays, yellows, browns, etc. When I had the base coat of colors down, I completely soaked the piece in a pva and water 50/50 mix to harden the pieces and give it a bit of protection. I then started layering on dirt (dried coffee grounds from my pot), dried leaves (black tea and mulling spice and dried oregano) and finally added some moss to the rocks using the basic Woodland Scenics flock. I again coated the piece really well with the pva & water mix via a spray bottle. Finally I added some shading using some really, really watered down acrylic paint that I splashed on and allowed to run as it would naturally. I know I am missing a few odd bits of information, but I'll try to give an update in the near future.
If you don't know about this group yet, let me tell you about Miniature Modeling Mayhem. It is a fantastic group of guys from around the world who share ideas and interests in wargames and terrain building. We meet just about every night (if you want) via online video chats to share ideas, paint and talk history and other topics. I encourage you to check us out on Facebook and Google+.