• In this video, This Old House landscape contractor Roger Cook shows how to affix loose flagstones.

    1. Lift up and remove loosened flagstones.
    2. Use wire brush to scrub clean the concrete surface below the flagstone.
    3. Don safety glasses and use air compessor with air nozzle to blow dirt and debris from the concrete base.
    4. Apply concrete-block adhesive to the concrete.
    5. Use flat trowel to evenly spread out the adhesive.
    6. Apply bead of mortar-joint repair caulk around the perimeter edges of the flagstone.
    7. Set the flagstone into place and firmly press it down.
    8. Wipe the surface of the flagstone clean using a damp sponge.
    9. Fill any voids around the perimeter of the flagstone with mortar-joint repair caulk.
    10. Sprinkle mixture of sand and stone dust over wet caulk.
    11. Allow repair to cure overnight, then use a garden hose to rinse off the excess stone dust/sand mixture.
    12. Stay off the repaired flagstone for four or five days.
    • 2 to 4 hours, depending on the extent of the damage
    • 10 to $30, depending on the extent of the damage
    • Difficulty: Easy to moderate
      the repair itself isn't difficult, but working on your hands and knees gets old fast
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      Tools List

      • Wire brush, used to scrub clean the concrete surface below the flagstones
      • air compressor
        Air compressor with air nozzle, used to blow debris from surface of concrete base
      • caulk gun
        Caulking gun, used to apply adhesive
      • flat finishing trowel
        Flat trowel, for smoothing masonry adhesive
      • sponge
        Sponge, used to wipe the flagstone surface clean
      • push broom
        Broom, for sweeping flagstone clean after repair

      Shopping List

      1. Concrete-block adhesive, used to adhere flagstones to the concrete base

      2. Mortar-joint repair caulk, for sealing joints around flagstones

      3. Sand and stone dust mixture, used to blend mortar-joint repair caulk into surrounding area