This is what happens to Sandstone when the Pointing Company before you has not got a clue what mix to use!
January 12, 2016
Sand Blasting & Stone Repointing
Spalling occurs because hard cement without lime traps damp behind it, which soaks into the surrounding stone and freeze-thaws. The pointing should draw moisture out of the stonework and allow it to evaporate through the pointing. The pointing should "sacrificial" i.e. any water and frost damage should be confined to the pointing, which is replaceable