This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
As previously stated with respect to stone masonry, the strength of brick masonry is largely dependent upon the strength of the mortar; but, unlike stone masonry, the strength of brick masonry is, in a much larger proportion, dependent on the strength of the brick composing it. The ultimate strength of brick masonry has been determined by a series of tests, to vary from 1,000 to 2,000 pounds per square inch, using lime mortar; and from 1,500 to 3,000 pounds per square inch, using cement mortar - the variation in each group (for the same kind of mortar) depending on the quality of the brick. A large factor of safety, perhaps 10, should be used with such figures.