How to Repoint & Repair a Flue Pipe on a Chimney

Remove obstructions such as fire grates or dampers from the opening to your flue. Using a flashlight, carefully examine the mortar joints of the flue for missing mortar. Scrub the inside of the working area using the chimney brush to remove any creosote or dirt particles from the flue. Probe the joints for loose or crumbling mortar using the chisel and remove any loose particles of mortar between the masonry with the paintbrush.

Remove the mortar using the chisel and hammer. Place the chisel over the mortar joints so that it sticks almost straight out from the flue wall and strike it lightly with the hammer. Remove the mortar from the joints between your masonry to a depth equal to twice the width of the mortar. Begin working on the vertical joints before moving on to the horizontal joints. If there is loose mortar in the joints that is deeper than the recommended depth, remove it using the paintbrush.

Prepare a cement mortar mix according to the manufacturer's instructions. Dampen the joints that you removed mortar from using a cup of water and the paintbrush. Place a layer of mortar on your mortar board and begin applying it to the masonry joints using the trowel.

Scoop a glob of mortar onto an end of the trowel and lightly press the mortar and the end of the trowel into the beginning of the joint. Scrape the trowel along the length of the joint, pressing the mortar in between the masonry as you go. Scrape any excess mortar off the outside of the bricks. Apply mortar to each joint until it is full and then use the trowel to level the surface of the joint. Repoint the vertical joints before you work on the horizontal joints. Apply fresh mortar in layers to any joints where you removed more than the recommended amount of mortar before moving on to the other joints.