How to Repair a Flagstone Path

Position a cold chisel so that the pointed end touches the mortared joint of the slab in the flagstone path that requires repair. Hold a hammer in your other hand, and tap the end of the chisel with the hammer to break up the mortar surrounding the broken flagstone slab. Scrub the joints with a stiff-bristled nylon brush to clean out any residual mortar and other debris. Wipe the joints down with a wet sponge.

Strike the chipped or cracked flagstone slab with a hammer to break it into small pieces. Lift the flagstone pieces away. Measure the size of the hole, then mark those measurements on a fresh slab of flagstone. Chisel along those measurements with a cold chisel and hammer to break the slab down to the necessary size.

Prepare mortar in a wheelbarrow, according to the manufacturer's instructions. Use a trowel to spread a ½-inch thick layer of mortar across the hole. Position the new flagstone piece on top of the hole and press it down into place. Use a level to ensure the flagstone piece is even with the other slabs in the path. Allow the mortar to dry overnight.

Combine mortar mix with acrylic fortifier in a wheelbarrow. Follow the acrylic fortifier product manufacturer's directions to determine the proper ratio to add to the mortar. Add water gradually to the mix and stir until the mortar mix attains a thick consistency resembling peanut butter.

Fill a grout bag with mortar. Position the end of the grout bag just above the slab joints and squeeze out the mortar in a 1-inch deep layer to fill the joints. Press down on the mortar with the back of your trowel to compact it into the joints. Scrape off any excess mortar with the side of your trowel. Clean off any residual mortar on the flagstone slab with a wet sponge. Allow the mortar to dry for at least one hour.

Press down on the mortared joints with a tuck-pointing trowel to compact and smooth the mortar further. Clean off any excess mortar with a wet sponge. Use a stiff, natural bristle brush to even out any bumps or uneven sections in the mortar. Give the mortar a full week to dry.