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How to Repair Chimney Cracks

Whether you use coal or natural gas for your fireplace, a crack on your chimney could be dangerous. Most times, you may not discover a crack because it occurs at the topmost part of your chimney.

That’s why it is advised that you go up to your roof and inspect your chimney once a year.

A cracked chimney will let in ice, rain, and snow into your house. This will not only damage your roof but your ceilings and floors too. Sometimes a crack may cause a chimney fire.

It is quite serious because when it happens, you will need the help of a fire department to put out the chimney fire.

To avoid these unfortunate situations, it is advised that you inspect your chimney at least yearly. Does your chimney have a crack already? Don’t worry. 

Tools and Materials Required

  • Protective gloves
  • Safety glasses
  • Ladder
  • Hammer
  • Trowel
  • Mortar
  • Chisel
  • Water-based silane
  • Joint Raker
  • Caulk
  • Tuckpointing tool
  • Knife
  • High heat mortar
  • Garden hose
  • Paintbrush
  • Clean rags

6 Step By Step Instructions of How to Repair a Chimney Crack 

It doesn’t get easier than using the steps outlined below. Here we go:

  • Scrape and replace the loose mortar: Scrape out the old mortar with the help of a joint raker. Alternatively, you can use a chisel and hammer to make the task easier. Once that is done, use a garden hose to water the brick and wait for it to dry. Combine powdered mortar and a little water into a tray and mix until it forms a stiff mixture. Apply the mixture using a trowel. Interestingly, you can use a tuckpointing tool to smoothen the edges.
    • Pour caulk between the flue and crown: You may notice that there is a gap at the point where the flue and crown meet. Pour caulk and high heat mortar into this gap.
    • Repair cracks in the chimney crown: Rain, ice, and snow usually collect in the cracks around the crown. You can use a mixture of mortar and water to fix these cracks. Immediately you have mixed the mortar and water, use a knife to insert it into the cracks.
  • Use water-based silane to fix hairline cracks: Hairline cracks are quite smaller than the usual cracks you find on chimneys. Rain, ice, and snow cannot collect in these cracks. To fix a hairline crack, you need to pour water-based silane into these cracks. Before applying the water-based silane, use a knife to scrape away loose particles around the area. After that, you can apply the water-based silane but do not dilute it. This won’t only repair the hairline crack but will stop other cracks from forming. 
  • Fix chimney bricks crack: With just a high heat mortar, you can repair the cracks in your chimney bricks. Use a knife to scrape away the loose particles in the crack. After that, pour the high heat mortar into the crack and use a rag to clean the surrounding area. You can use a water-based silane instead of a high heat mortar if the crack is tiny.
  • Replace cracked bricks: If a brick has too many cracks, the best solution is to change it. Interestingly, you can remove a brick without disturbing the other bricks close to it. Using a chisel, break the mortar between the bricks. Once the brick becomes loose, you can use your hand to pull it out. 

How to Repair a Chimney Cap

Apply mortar on the sides of the new brick using a trowel. After that, use the new brick to replace the old one. Finally, use a tuckpointing tool to smooth the edges.


Don’t forget to practice all the safety measures when repairing your chimney cracks which include wearing protective gloves. Also, if you sweep your chimney yearly as recommended by the CSIA, you would identify these cracks on time too. 

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