How to Fill Mortar in a Stone Foundation

Rather than concrete, many older homes have natural stone foundations. Over time, the aging mortar in stone foundations can begin to crumble. Holes can form, inviting moisture to seep through the wall and threaten even more damage. Ensure the structural integrity of a home’s footing by filling in any gaps in the joints between stones with new mortar. Professionals refer to the process of repairing masonry joints as “repointing.”

Hammer
Chisel
Stiff brush
Lime mortar
Pointing trowel
Joint tamper
Jointer tool, tuckpoint trowel or caulk trowel

Instructions

- 1
  Set the sharp tip of the chisel into the damaged mortar joint. Tap the back of the hammer to chip out chunks of damaged mortar. Move the chisel around while continuing to tap the back to dig out the mortar joint. Eliminate the mortar to a depth of approximately 3 inches in all places where mortar is to be refilled.
- 2
  Ensure that all crumbly bits of mortar are gone by brushing out the hollowed joints with a stiff brush.
- 3
  Mist the areas to be repaired lightly with water to dampen them.
- 4
  Fill the hollowed joints halfway with lime mortar, using a pointing trowel. Pack the mortar in by tamping it repeatedly with a point tamper. Leave the mortar to sit until it just starts to stiffen.
- 5
  Fill the joints the rest of the way with additional lime mortar. Compress and smooth the mortar at the surface by running the wand of a jointer tool, tuckpoint trowel or caulking trowel down the joints, applying firm pressure.
- 6
  Scrub the surfaces of the surrounding stones with the stiff brush to remove any smeared mortar.

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