We study arrangements of the two species of discs in binary assemblies
at an intermediate scale, Small discs rearrange along large ones in c
lusters whose mass and compactness are analyzed with the tools of perc
olation. The assemblies are generated analogically on an air table or
numerically from RSA or Powell algorithms. At a given packing fraction
, an infinite cluster of small discs exists above a critical compositi
on; a phenomenological expression for this threshold is proposed. Like
in usual percolation problems, the number of inner links in a cluster
is a linear function of its mass, with a slope depending both on the
packing fraction, the composition of the mixture and the building proc
edure. An approximate expression is derived for it.