JohninKansas usually has lucid and comprehensive explanations so I'm surprised he left out the (possible) effects of expansion of the mortar during the curing process. It's a very long time since I had the formulae and figures for such calculations but I seem to recall that this also imposed a limit on the overall length of a brick wall (of any height) without expansion joints in it. When I was at La Trobe Uni (Melbourne) the gossip was that the Admin building (I forget whose name it carried) had the longest brick wall with no expansion joints. Like many such boasts it was qualified with "in the sountern hemisphere" but it was a very long wall.

Cheers, Rowan