How to Fix Crumbling Chimney Mortar

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Avoid extensive, costly damage to a masonry chimney. Maintain the mortar joints by tuck-pointing (repointing) them, and make sure the chimney crown remains sealed against water.

Things You'll Need

  • Crown Repair And Sealing Material
  • Jointing Tool
  • Brick Trowel
  • Mortar Mix
  • Soft Brush
  • Cement-mixing Container And Hoe
  • Grinder With Tuck-pointing Attachment And Blades
  • High-temperature Caulk And Caulking Gun
  • Ladders Or Scaffolding
  • Mason's Hammer And Chisel
  • Pointing Trowel
  • Scraper
  • Square Mason's Trowel Or Board
  • Work from the bottom up to remove loose mortar a few feet (a meter or so) at a time. Set up ladders or scaffolding if necessary. Use a mason's hammer and chisel, a scraper and similar hand tools for difficult-to-reach areas. For extensive tuck-pointing, rent an electric grinder with a tuck-pointing attachment and blades.

  • Mix water into a packaged mortar mix as directed on the label, using a cement-mixing container and hoe.

  • Apply the mortar by first loading the bottom side of a square mason's trowel (or a board) with mortar (see A). Then, holding the trowel against the chimney just below the joint you're filling, slice off a portion of the mortar with a pointing trowel and pack it into the joint.

  • When the joints in an area are all full, strike off the excess by slicing through the mortar with a brick trowel held flat against the bricks.

  • Compress, shape and smooth the joint. Run a jointing tool across the joints for concave and V joints (see B). Or use the tip of a pointing trowel to create a 30-degree bevel from the underside of the upper course to the edge of the lower course. Knock off any excess and move up to the next section.

  • When the joints have set up, clean the face of the brick with a soft brush.

  • If a traditional crown made of portland cement and sand is badly eroded or cracked, replace it with a modern (crown-sealer) system. These coatings, which you can apply with a trowel (following the manufacturer's instructions), remain flexible and provide a far superior water seal. If the crown has some cracks and is beginning to show wear, or even if a masonry crown is in good condition, consider using this material as part of an overall chimney repair.

  • Seal joints between the clay flue's liner and the crown with high-temperature caulk.

Tips & Warnings

  • For very minor tuck-pointing repairs, use mortar-patching material in caulking-gun cartridges.
  • Exercise caution and follow proper safety procedures when working on a ladder or scaffolding.

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