How to re-cement flagstone

Written by sal marco
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How to re-cement flagstone
Repairing flagstone saves money over replacement. (strasse image by Tubeless from

Flagstone is a type of natural stone that is commonly used to make patios and sidewalks. Flagstone is available in many sizes and shapes, making installation much like fitting together pieces of a puzzle, and when one piece is missing, it becomes obvious and ruins the look of the structure. Over time, exposure to weather conditions and accidental damage, flagstone loosens and becomes unstable. Repairing and re-cementing flagstone restores the beauty and is virtually undetectable.

Skill level:

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Things you need

  • Pry bar
  • Wire brush
  • Bucket or trough
  • Tape measure
  • Trowel
  • Level
  • Grout bag

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  1. 1

    Remove the loose piece of flagstone from the patio or sidewalk by lifting it up with your hands, or wedge a pry bar in between the stones and pry it up.

  2. 2

    Use a wire brush to remove old cement and debris from the back of the flagstone and from the existing flagstone surrounding the area from which you removed it.

  3. 3

    Remove broken pieces of old cement from the base of the hole.

  4. 4

    Mix ready-mix concrete according to the directions on the bag in a bucket or trough.

  5. 5

    Use a tape measure to determine the distance from the base of the hole to the top of an adjoining piece of flagstone. Subtract the thickness of the flagstone from the height measurement to determine the amount of cement required for the base of the hole. This will keep the patio level and free of tripping hazards.

  6. 6

    Mark the side of the existing flagstone using the difference between the two measurements minus 1/2 inch.

  7. 7

    Fill the hole with cement up to the mark.

  8. 8

    Apply 1/2 inch of cement to the removed flagstone with a trowel.

  9. 9

    Set the flagstone into the hole and press it in firmly.

  10. 10

    Place a level on the replaced flagstone. If the bubble on the level is off-centre, adjust the flagstone in the appropriate direction by tapping on the high side until the bubble centres.

  11. 11

    Fill a grout bag with wet concrete and squeeze concrete into the space around the flagstone.

Tips and warnings

  • Allow the concrete to set for 10 to 12 hours.
  • Wear safety goggles and gloves when working with concrete.

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