Is it possible to have two different bumps within the same shader?  Let me give you an example.  Lets say I want to make a really good brick shader.  Once I get the colors down now I need to have a very fine bump for the grout and a larger bump for the bricks.   I have tried mixing the bump channel with the Mixer operator, but that didn't work.  I also tried using layers, but again there is something I'm not understanding because that didn't work for me either. Here is my attempt with the mixer in the bump channel.  Can anyone tell if its possible to do this?  If so, how?!

Thanks
Mike