The weather leads sooner or later to the loosening of the sealed tiles covering the fence walls. Repair locally avoids more serious damage.
Blow up the mortar with the chisel under the ridge tile. Remove the broken tiles and stake their support surface.
Put a piece of chevron on the wall to facilitate the installation and alignment of new tiles.
Recolete the split tile with epoxy glue (two-component mix) and hold with a clamp.
Cut the back rib of the new tiles to make them slip under the ridge.
Strike a cement mortar until it is unctuous and spread it with a trowel over the entire thickness of the wall.
Dip the tiles in the water for 5 minutes then slide them under the ridge while pressing them on the mortar bed.
Prepare a lime-based mortar and complete the ridge seal with a cat-tongue trowel.
Smooth the seal with a damp sponge or let the mortar dry for a few hours before smoothing it with the soft brush.