Sometimes a brick chimney has a fracture running through it, which means it is broken. The mass of masonry above the fracture is just resting on top of the masonry below, with no mortar bond effective there to hold things together. It is susceptible to smaller earthquakes that could send it toppling over.
The city of Los Angeles came out with a standard plan for how to deal with a broken chimney after the 1994 Northridge earthquake. All of the cities in the LA area recognize this plan as the standard way to rebuild a chimney.
It involves demoing the chimney down either to the roofline or to the top of the smoke chamber. (the space above the firebox) There one constructs a concrete “bond beam” on top of the remaining brickwork and then installs metal flue components so that one ends up with a round metal flue pipe which will carry the
smoke up and out the top. One constructs a steel-framed chimney chase enclosure to hide the pipes. The outside of the enclosure is often coated with stucco. Or it can be finished with a brick veneer, so that the final product looks very much like the original brick chimney.
We do these types of rebuilds and are very good at it. If you need this kind of repair, give us call.