  We present a novel experimental protocol using Cathodoluminescence
measurements as a function of the electron incident energy to study both
exciton diffusion in a directional way and surface exciton recombination. Our
approach overcomes the challenges of anisotropic diffusion and the limited
applicability of existing methods to the bulk counterparts of 2D materials. The
protocol is then applied at room and at cryogenic temperatures to four bulk
hexagonal boron nitride crystals grown by different synthesis routes. The
exciton diffusivity depends on the sample quality but not on the temperature,
indicating it is limited by defect scattering even in the best quality
crystals. The lower limit for the diffusivity by phonon scattering is 0.2
cm$^{2}$.s$^{-1}$. Diffusion lengths were as much as 570 nm. Finally, the
surface recombination velocity exceeds 10$^{5}$ cm$^{2}$.s$^{-1}$, at a level
similar to silicon or diamond. This result reveals that surface recombination
could strongly limit light-emitting devices based on 2D materials.
