  The properties of fully-heavy arrangements including a number of quarks
between 5 and 12 were calculated within the framework of a constituent quark
model by using a diffusion Monte Carlo technique. We considered only clusters
in which all the quarks had the same mass, and whose number of particles and
antiparticles were adequate to produce color singlets. All the multiquarks were
in their lowest possible values of $L^2$ and $S^2$ operators. This means that
we considered only color-spin wavefunctions that were antisymmetric with
respect to the interchange of {\em any} two quarks of the same type. We found
that in both all-$c$ and all-$b$ multiquarks, the mass per particle levels off
for arrangements with a number of quarks larger of equal than six. The analysis
of their structure implies that the fully-heavy multiquarks are compact
structures.
