Mix the mortar; it should be the consistency of cookie dough, not too dry and not soggy.
Note: Refer to the resources listed below for tips on mixing mortar.
While the mortar rests, prep the area by clearing away any loose debris.
When applying the mortar to the crown, form the mortar into an apex with the peak at the middle of the crown sloping down toward the edges. Think of it like a roof: the idea is to have the water drain away from the crown (Image 1).
Note: Don’t make the edge too thin; keep the edge at an approximately 1/2"-3/4" height to prevent it from possibly detaching later. Also, use the mortar to seal up any holes around the crown (Image 2).
Let the mortar to cure for several hours before doing any further work on the crown.
To begin restoring the brick mortar joints, a process commonly known as tuck pointing, first prep the area to ensure good mortar adhesion (Image 1).
Apply the mortar to the joint using a pointing trowel, if one is available. Fingers often work as the best tool for some of the tighter joints (Image 2); just make sure the mortar is tightly packed each time it's applied.
Clear away excess mortar (Image 3), making sure it fills the void and stays in place.
Note: Continue to keep the mortar churned and at the right consistency throughout the process.