What happens when you use the wrong mortar on brick

Hubby previously mentioned 'spalling' of brick caused by using a mortar mix that was too hard for the bricks to expand and contract, causing the surface of the brick to shatter, and eventually disintegrate. I took some photos of our brick and of a brick house built within 6 months of our home in the same neighborhood.

Ok, kids, let's play 'Bad Mason/Good Mason'.

Bad Mason:













Up at the top of this wall, the sparrows have dug small nests into the brick where they've dug out the soft brick.














Below: good Mason: Puuuuuurdy brick. :-)