Blending Normal Maps
combine normal maps blend normal maps
ShaderMap 2 currently implements overlay and detail oriented methods (called pure rotation in SM2) for painting normals. I may do a write up of the SM2 blending modes and maths behind them in the future.
In the meantime here is a really great article I found on blending a detail normal map with a base normal map. http://blog.selfshadow.com/publications/blending-in-detail/
In other news, I'm on Google+ here: Neil Kemp
and I've started a G+ page for ShaderMap as well: ShaderMap+