How to Reseal a Chimney for Furnace Venting

Many older model furnaces are vented through a home’s brick chimney. To prevent breakage and leaks, brick chimneys are often sealed with rubber or tar coating. Over time and exposure to the elements, the original coating begins to fail and causes chips and cracks to occur on the bricks and mortar. Keep your furnace vented effectively by resealing the brick chimney. Prepare the chimney bricks and mortar before applying the first layer of replacement sealant.

Wire brush
Hand broom
Caulking gun
Roofing cement
Rubber coating primer
Paint rollers
Rubber elastomeric coating

Instructions

- 1
  Examine the chimney and remove any loose debris or mortar from the chimney with a wire brush. Brush away the remnants from cleaning with a hand broom before attempting to reseal the chimney.
- 2
  Load a caulking gun with roof cement. Pull back the gun's trigger and fill any cracks and missing mortar on the chimney with the product. Press the end of the cement’s tube into the crack to ensure it’s completely filled.
- 3
  Repair any cracks or missing mortar on the area between the chimney and roof with the roof cement. Allow the roof cement to dry for at least 12 hours before continuing.
- 4
  Cover the chimney with a thin layer of rubber coating primer to the entire chimney’s surface, including the metal flashing between the chimney and the roof with a paint roller. Allow the primer to dry for at least eight hours, or overnight.
- 5
  Apply a thin layer of rubber elastomeric coating over the dried primer with a paint roller. The elastomeric coating resists corrosion, moisture and weathering. The product’s drying time is dependent on the brand, temperature, wind, humidity and several other factors.

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