Introduction

smoothing fresh mortar joints with a brush
Photo: John W. Taylor
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Q: The mortar joints surrounding the stones in my walkway are crumbling. Can they be patched? —Nellie Kurtzman, Mount Vernon, NY

Martin D’Arcy, owner, DNF Construction, replies: A stone walkway with cracked mortar is an eyesore and can become a tripping hazard if water gets underneath and loosens the stones.
The best way to repair these joints is with a sand-topping mortar mix, which is stronger than regular mortar and can handle wider joints. I mix it with an acrylic fortifier so that the joints will be less susceptible to water penetration.
The hardest part of this job is chipping out the crumbly old mortar without damaging the stones. Once the old stuff is out, filling the joints is as easy as decorating a cake. Just keep in mind that while the new mortar won't match the existing mortar color, it will lighten and blend in over time. The only way to get the same shade would be to replace all the old mortar, crumbling or not.
Tackle this job only when there’s no danger of frost. A two-day dip into the 20s F can ruin fresh mortar.

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    Tools List

    • safety glasses
      Safety glasses
    • gloves
      Gloves
    • knee pads
      Kneepads
    • 3-pound hammer
      3-pound hammer
    • mason's chisel and maul
      Masonry chisel
    • mason's brush
      Masonry brush
    • one-and-a-half inch paintbrush
      Paintbrush
    • brick trowel
      Brick trowel
    • grout bag
      Grout bag
    • pointing trowel
      Tuck-pointing trowel
    • mortar pan
      Mortar pan

    Shopping List

    1. 60-pound bag of sand/topping mix

    2. 1 gallon of acrylic fortifier

    3. Water