Unless someone has the gift of intimate experience with chimneys in this area, diagramming the situation might be a good idea.

Description of the situation

1. A brick on the angled exterior shoulder of the chimney dislodged.

2. The old lime mortar on the inside flank of that brick was broken where it went under the stucco of the house wall and then met with the 15 pound felt paper facing the exterior studs of the house wall.

3. The 15 pound felt paper on the exterior studs has a U channel metal flashing at the bottom which it overlaps vertically a bit. The U flashing runs diagonally and upward toward the center of the chimney and appears to function as a drain for water collected from the felt paper and, perhaps, the chimney mortar which extends down into the U.

4. There appeared to be a 1/8" or less air gap between the felt paper and the outer brick mortar face. Was this the unimportant result of natural shrinkage of the old lime mortar? Or is this air gap a design element that must be maintained when replacing the old lime mortar?

5. If this air gap is an important design feature, how do I establish it when putting in new type S mortar when I only have restricted access from the top of this opened area? Is there any material I can temporarily insert between the wall felt and new mortar to establish the gap and then remove without disturbing things?

6. Note that the felt paper in place was ripped when removing some of the old lime mortar. Although the old felt paper is no longer tight, I have repaired the tear with waterproof caulking and it seems fairly strong. If I can maintain an air gap between the wall with its 15 pound asphalt felt and the new mortar, a problem is unlikely. However, if the weight of the setting mortar bears directly on the patched paper which is no longer taut, I am more concerned.

7. There is about 1" room to push a new, 2-piece patch of 15 pound paper under the old paper beneath the upper section of opened stucco wall.No end pieces of existing felt are in place for this patch to side lap under. These sides of the patch would have to be caulked and stapled to upright studs and the bottom left to overlap the top part of the U channel flashing below. At best, each section of the patch would have two points of attachment on each side. I'll use staples or galvanized nails for that. If anyone argues a preference for one fastener type over another, I'm listening.

Any and all thoughts and observations would be appreciated. If someone is familiar with the best approach in this situation from intimate experience, I would be more than grateful for any advice.