Severe weather condition causes old mortar to crumble which becomes porous. If this happens, it will require repointing. Remove any loose mortar with the point of your pointing trow, damping the wool with water to avoid the quick drying out. Use small amounts of mortar on your pointing trow and position carefully between the bricks. Take care not to get mortar on the brick fences. Apply in mortar in small amounts in between the vertical joints to begin with. After the vertical joints have been repointed, start on the horizontal joints. You might practice the pointing up procedure in a small and conspicuous area before attempting a large prominent area. remove any excess with the edge of the trow.