Mortar Joint Repair Tips
Deteriorating Mortar Joints
More common than bulges and cracks are deteriorating of the mortar joints between bricks. The mortar crumbles and crumbles out. The problem is especially prevalent in houses built before about 1930 when the mortar used was lime putty. Portland cement, which is a stronger binding agent, was not used. Water or acid leaches the lime out of the old mortar and, eventually, the mortar must be replaced.
To test the integrity of the mortar joints, poke them with an ice pick. If the mortar seems Sandy and falls out easily, the joints have deteriorated to the point where you have to do something. If you don't correct the problem, moisture will continue to work into the brickwork, eventually causing more deterioration that requires even more work.
If the brick, the mortar, or both are deteriorating, you have three choices: Re-point the mortar joints, cover the entire brick face and joints with stucco, or touch up the worst of the damage and apply paint. The cheapest alternative is to repair and paint, the second cheapest is to apply stucco, and the most expensive is to re-point.
Pointing is often favored because it retains the original look of the wall; in some historic districts, this is mandatory. Moreover, if you decide to stucco or paint, you still probably will have to re-point the worst of the joints to maintain the integrity of the wall.