How to Fix the Mortar on a Chimney

Inspect the chimney for cracked and crumbling mortar, taking note of all the joints requiring repair. Plan the chimney repair so it proceeds from bottom to top and in small sections. Removing too much mortar at once can weaken the chimney's structural integrity.

Remove the damaged mortar from the joints between the bricks in your first section of chimney. Badly degraded and crumbling mortar can be pulled out with your fingers and a plastic brush, but tougher mortar might require scrubbing with a wire brush. Cracked mortar or clinging bits of mortar must be chipped out with a hammer and cold chisel; but take care to avoid damaging the brick. You may find it necessary to remove entire bricks to clean out damaged mortar.

Mix a batch of mortar in a bucket or small tub sufficient to fill the empty joints in your chimney section.

Fill empty joints by pouring mortar into a mortar bag. Insert the nozzle into the joint and squeeze the mortar bag to force mortar through the nozzle, operating it as you would a cake decorator. If you must put a brick back into the wall after removing all the surrounding mortar it, skip to Step 5.

Replace removed bricks. Simply spread a flat bed of mortar onto the bottom of the empty space with a masonry trowel, matching the thickness of the mortar in the surrounding joints. Spread mortar across the sides and top of the brick in the same thickness and push the brick into the space.

Scrape excess mortar off the face of the wall with the trowel. Sculpt the surface of the wet mortar to match the style of the old mortar if the old mortar has such a style, like a slanting face.

Remove and replace mortar, section by section, until the chimney is repaired.