wikiHow to Fix Crumbling Chimney Mortar

Brick is a sturdy, long-lasting building material. However, the mortar that holds bricks together, a mixture of cement and sand, can weaken and crumble. Repairing the crumbling mortar before the bricks fall is called tuck-pointing or re-pointing the bricks. To fix crumbling chimney mortar, follow some common steps.


  1. 1
    Clean the damaged area. Use a stiff-bristled scrub brush and a mixture of either regular dish soap or commercial brick cleaner and water to scrub the bricks and joints in the area(s) where you will be re-pointing the mortar. Allow the surface to dry completely before moving on to the next step.
  2. 2
    Remove the damaged mortar from the joint(s) that you are going to repair.
    • Scrape as much loose mortar out of the joint as possible using a wire brush.
    • Chip the remainder of the old mortar out of the joint very gently using a hammer and a chisel.
    • Brush the brick thoroughly with a dry scrub brush to remove any small pieces of mortar and mortar dust.
  3. 3
    Apply a thin layer of commercial bonding agent to the exposed surface of the joint(s) that you are repairing.
  4. 4
    Prepare the mortar according to the manufacturer's instructions as found on the package. Mortar is properly mixed and ready to use when it is moist enough that it holds together without crumbling. Mortar will start to harden, or set up, relatively quickly. Mix it in small batches to avoid having it dry out in the middle of the repair.
  5. 5
    Apply the fresh mortar to the joint using a trowel, and force it in using a joint strike. Repeat this until the entire joint is packed full of new mortar, and the joint is level with the brick.
  6. 6
    Finish the joint by running a gloved finger along the joint to remove the excess mortar. The mortar line should be slightly indented below the surface of the bricks.


  • If you need to fix crumbling chimney mortar on more than one section of the chimney or on multiple chimneys, consider using a power washer to clean the brick instead of scrubbing it by hand. You can get comparable results with significantly less effort.
  • Mixing the mortar can cause a significant amount of dust to become airborne. Wearing a dust mask while you mix the mortar will limit the amount of dust that you inhale.
  • If you accidentally drop mortar compound on the sidewalk when you fix crumbling chimney mortar, it can be removed. Wait for it to dry and remove it with a muriatic acid wash. Be sure to use gloves and eye protection; any acid can be dangerous.


  • Always wear heavy work gloves and eye protection when scraping damaged mortar out of the joint to prevent injuries.
  • Always wear gloves and eye protection when working with commercial bonding agents to avoid severe injuries and/or blindness.

Things You'll Need

  • Stiff-bristled brush
  • Dish soap or commercial brick cleaner and water
  • Eye protection
  • Work gloves
  • Wire brush
  • Hammer
  • Chisel
  • Commercial bonding agent
  • Drill with mixing paddle
  • Mortar mix
  • Bucket or other container to mix mortar in
  • Joint strike

Article Info

Categories: Concrete | Exterior Walls and Roof