The first step of the process is to remove the existing plaster. The old mortar must be removed with a hammer and chisel or similar tools before applying new ones. Some fireplaces have brick linings, which will need to be replaced as well for maximum efficiency. Then the new mortar will be applied with a trowel. It is important to allow it to dry for several days before continuing the process.
Next, you can begin installing your firebox and chimney liner/cap (if needed). A standard gas fireplace generally does not need a flue cap; however, wood burning stoves require one in order for proper draft to occur when they are used as designed. If your installation choice includes an exterior vent or chimney, then ensure that it has been installed by someone who knows what they are doing so there aren’t any major leaks once everything is finished up!