Material ID of Caps Of Fractures or Bricks not working properly

[makco]

Not quite sure I understand what you mean, but you can assign any material IDs to any particles you like, either in the voronoi settings or with a material ID operator. There is no limit to the number of material IDs you can have in a flow (well there is, but it's around 16000...hopefully you dont need that many )

Ok maybe I haven't fully digged in to the materials options... I'll check more about what one trying to do and get back to you if still can't find the way. 

Yes 16000 would be more than I need !!

M