Maps
Workflow:
I just used some photo's from CGtextures as base. Then I added extra detail by making a new layer with moss and setting it on overlay. I brushed away some parts I didn't need, so that the moss only showed at the sides.
For the normal map I just used the normalmap filter. I don't think it came out very well but I don't have Crazy bump anymore... I miss my Crazybump
For the specular I just desurated the Diffuse map and made certainly parts light and contrastyer.