Steps:
- Lift up and remove loosened flagstones.
- Use wire brush to scrub clean the concrete surface below the flagstone.
- Don safety glasses and use air compessor with air nozzle to blow dirt and debris from the concrete base.
- Apply concrete-block adhesive to the concrete.
- Use flat trowel to evenly spread out the adhesive.
- Apply bead of mortar-joint repair caulk around the perimeter edges of the flagstone.
- Set the flagstone into place and firmly press it down.
- Wipe the surface of the flagstone clean using a damp sponge.
- Fill any voids around the perimeter of the flagstone with mortar-joint repair caulk.
- Sprinkle mixture of sand and stone dust over wet caulk.
- Allow repair to cure overnight, then use a garden hose to rinse off the excess stone dust/sand mixture.
- Stay off the repaired flagstone for four or five days.