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How to Repair Chimney Crown Mortar

Updated February 21, 2017

One of the most important elements of a brick or masonry chimney structure is the crown mortar, which acts as a sloped seal to drain rainfall off of the top surface of the chimney. Over time, this mortar cap can deteriorate and develop cracks that open the masonry to more extensive damage. Once the mortar crown has reached the point of decomposing, the best repair is replacing the crown to restore its function.

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  1. Access the chimney and chip away the old mortar crown using a hammer and cold chisel, then clear the chimney’s top surface of dust and debris with a stiff-bristled broom.

  2. Mix the mortar mix in a wheelbarrow, using a hoe or shovel, following the manufacturer’s specifications. The mortar should be slightly stiff, or “dry,” and about the consistency of peanut butter.

  3. Transport the mixed mortar to the roof using a 5-gallon plastic bucket, available at most home improvement centres, and position the bucket of mortar on the roof behind the chimney for easy access during application.

  4. Spread mortar over chimney top surface using a trowel, sloped away from the clay chimney pipes to the outer edges. Maintain a minimum slope of 2 to 3 inches per linear foot, keeping the surface smooth with the trowel.

  5. Allow the new mortar crown to set for a minimum of 24 hours before proceeding.

  6. Apply a coat of elastomeric concrete sealer to the surface of the mortar crown using a paint brush, making certain the coating laps onto the clay chimney pipes at the top and onto the masonry sides of the chimney structure. Allow the sealer coat to dry following the manufacturer’s recommendation.

  7. Tip

    A second full coat of elastomeric sealer can be added, if desired, for additional waterproofing protection. Excess mortar that falls onto the roof surface can be rinsed off with a garden hose.

    Warning

    Chimney crown repair involves working on the roof surface and extreme care should be taken to maintain secure footing. Keep tools and materials positioned behind the chimney structure to prevent damage or injury.

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Things You'll Need

  • Ladder
  • Hammer
  • Cold chisel
  • Stiff-bristled brush
  • Wheelbarrow
  • Hoe or shovel
  • Mortar mix
  • 5-gallon plastic bucket
  • Trowel
  • Elastomeric concrete sealer
  • Paint brush

About the Author

Paul Massey has been writing since 2009, drawing on a 35-year career in the construction industry. His experience includes 15 years as a general building contractor specializing in architectural design, custom homes, commercial development and historic renovations.

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