Multiple materials on one mesh(c#)

Hi!
I am beginner unity programmer and i have a question about meshes created runtime - how do i, in bounds of one mesh(MeshFilter.mesh) can assign multiple materials to different faces?
Reason why i am asking how to do this in single mesh is here:

As you can see i have (obvious minecraft clone thingy, just interest and experience) huge amount of geometry, all this generated runtime and i need to render this fast. So i have smaller chunks of geometry(one chunk is 64x64x32), and each one is one big mesh(so unity can batch it pretty good). But how can i assign different materials to different faces?

Thanks!

 

Found answer

 

What was the solution?