How to Replace Mortar Between Basement Blocks

Angle a cold chisel at a 45-degree angle and wedge it into the weak mortar joint in between the basement blocks.

Strike the end of the chisel solidly with a rubber mallet or hammer to break off 1 inch of mortar from the joint. Check the newly exposed mortar with your hand. If it is weak and crumbling at this level, continue to chip away until you reach a solid point.

Remove the chippings of mortar from between the basement block joints with a wire brush.

Pour some premixed mortar powder and water into a plastic bucket in the proper ratio as instructed on the packaging. Stir the powder and water with a shovel until the mortar reaches a uniform consistency.

Lift the wet mortar out of the bucket and apply it into the joint between the blocks with a pointed trowel, using the tip of the trowel to pack the mortar in a 1/4-inch layer. After 15 minutes, apply a second 1/4-inch layer of mortar. Continue to add 1/4-inch layers of the mortar with 15-minute curing periods in between the layers until the mortar is level with the block. Mortar will cure fully within 48 hours.