The most common scaling mechanisms are:

• Classic freeze-thaw scaling, where sub-horizontal micro-cracks leads to loss of material by flaking.
• Micro-delaminations, where very thin layers of mortar detach in coherent sheets from the top surface.
• Mortar flaking, which involves the loss of mortar over coarse aggregate particles.

Why should you read this? Meaty, technical article on a common challenge. FCP, December 2014