Fix-It Chick: Repoint damaged mortar joints to save brick, stone structures
Avoid costly damage to brick or stone structures by repointing loose, cracked or crumbling mortar.
Step 1: Use a cold chisel and a hammer to clean out the mortar joint to be repaired. Place the chisel next to the brick or stone and angle it toward the center of the joint before striking it with the hammer. Clear the area to a depth at least twice that of the mortar joint width. Brush away any loose material before proceeding.
Step 2: Mix clean, potable water into the dry mortar mix. Avoid chemical additives when repointing. Mix mortar in small batches, mixing only what can be used in half an hour. Mix mortar to a thick, butter-like consistency that smooths nicely when the bottom of a trowel is run over it. For most projects a premixed Type N mortar, which is typically one part Portland cement, one part hydrated lime and six parts sand, will work fine. Be aware that using cement-based mortar on older structures will cause irreparable damage. If the structure is over 75 years old, consult a preservation specialist to determine the correct mortar mixture.
Step 3: Mist the brick or stone area to be repointed. Place a lump of prepared mortar on a plastering hawk or on the bottom of a flat trowel. Place the edge of the hawk or trowel against the brick or stone edge. Use a narrow tuck-pointing trowel to press a thin layer of mortar into the joint. Fill the joint with one quarter inch of mortar at a time. Press it firmly into the joint and mist the area as needed to keep it moist but not wet.
Step 4: Once the joint is filled flush with the brick or stone surface, allow it to set until a print is formed when a thumb is pressed into the mortar. This process may take anywhere from 30 minutes to 24 hours.
Step 5: When the mortar is firm enough, use a jointing tool or dowel rod to rub the surface to smooth it to a shine. Lightly brush the surface with a stiff bristle brush to give the new mortar a weathered look.
Step 6: Wipe away any excess mortar from the brick or stone area and clean all tools immediately with cold water. Keep the mortar joints moist for at least a day to facilitate curing and reduce shrinking.
— Have a home improvement question for Fix-It Chick? Email it to Linda Cottin at firstname.lastname@example.org.