What term describes damage caused by strong osmotic pressures breaking building material apart?

The term that accurately describes damage caused by strong osmotic pressures breaking building material apart is indeed spalling. This phenomenon occurs when moisture penetrates the material, and as it evaporates, it creates pressure that can lead to pieces of the material flaking or breaking off. This is commonly seen in concrete and masonry, where the internal pressures from trapped moisture can cause sections of the material to detach, resulting in visible deterioration.

Other terms related to damage in building materials address different processes. For instance, efflorescence refers to the white, powdery residue often left on surfaces due to the evaporation of water, carrying salts from within the material; it does not involve the physical breaking apart of the building material itself. Cracking is more generic and can result from various factors such as settling or thermal expansion, while weathering is generally a broader term encompassing the gradual deterioration of materials due to environmental conditions without specifically focusing on osmotic pressures. Thus, spalling is the most precise term that captures the essence of the damage described in the question.