Any masonry surface with mortar in the joints between elements will need repair sooner or later. Brick, stone, concrete blocks, tiles and other pavers generally are durable and resistant to damage from water or use. The mortar between them, however, is more porous and more subject to deterioration as water penetrates and freezes. This causes cracks that eventually break out pieces of mortar, making pavers loose and unstable. This is especially true in joints that were "dry-grouted," with loose mortar swept into them and sealed with water. The solution is a repair called repointing. Repoint a patio much the way you would a brick or stone wall.
Things You'll Need
Garden hose with fine misting nozzle
Paintbrush and water bucket
Bucket or big container
Small-pointed mason's trowel or tuckpointing trowel
Steel finishing tool
Chip out loose or damaged mortar, between bricks, flagstones or other patio pavers. Use a cold chisel and hammer or a masonry grinder in a power drill to break out all loose or cracked mortar. Sweep it out with a whisk broom and finish with a shop vacuum to remove all old mortar and dust.
Buy a type of mortar that matches the existing undamaged joints. Look for packaged mortar designed specifically for patio pavers and some that does not have an extremely high cement content; mortar in pavers needs to be solid but not so rigid as to prevent all movement from heat and cold expansion and contraction.
Spray the patio surface with water from a garden hose with a fine misting nozzle or dampen open joints with water and a paintbrush, depending on how big the joints are and how big the repair area is. Don't let water collect in the joints; just wet the edges of the bricks, stones or other pavers so the mortar will bond better.
Mix mortar in a bucket or big container until it is solid enough to stand alone but fluid enough to spread easily. Push it into the joint with a small mason's pointed trowel or a thin-bladed tuckpointing tool, depending on how wide the joint is. Fill the joint from the bottom to the surface of the paver. Repair really deep joints in stages, filling the joint partway and allowing it to set before adding another layer to the joint, until it's filled. Finish the joint with a steel pointing tool to level the mortar.
Fill repaired joints to the height of the paver surface if you're redoing an entire patio; a level surface of paver and mortar will best repel water. Match the existing joints if you're repointing a small area, but try not to create big depressions in mortar, as they will collect water and eventually require repointing again.