Resumen: In a recent work [C. Lozano et al. Phys. Rev. Lett 114, 178002 (2015)] segregation in an horizontally shaken granular layer was studied by analysing the particle-particle interactions in the simplest case possible of a two particles cluster. There, it was found that all clusters are transient (they eventually split if one waits long enough) and the probability distribution function of the separation times displays a power law tail, indicating that the splitting probability is not constant over time. Here, we extend this study to clusters of 3, 5, 10 and 20 particles where we also observe the power law decay of the distribution of cluster splitting time. In addition, we observe a weak increase of the average cluster splitting time with the cluster size, suggesting that interaction forces are non-additive. Finally, we show interesting statistics on the way in which clusters break suggesting that escaping of individual particles in the cluster borders is more likely than cluster breakage in subclusters of similar size.