Do It Yourself and Other Educational Chimney and Fire Safety Articles

Cracks in the chimney liner or mortar crown or fireplace (aka firebox):      

When cracks occur, hot gases can escape into the fireplace chase or into the home, sometimes causing carbon monoxide to enter your house. These gases also may cause nearby framing members to ignite. Gas entry and ignition can be prevented by having your fireplace inspected for cracks and faulty liners or mortar.  Clay flue liners are especially susceptible to cracks so if you have clay, you definitely need to have it fully inspected regularly.  This typically requires your chimney sweep to place a camera on a string and run it along the entire interior of the flue with proper lighting to get an accurate view.  It will be much cheaper in the long run to have your annual inspection than if a house fire occurs and then insurance declines to cover the cost due to your own negligence which they discover when assessing the damage and find cracks.

Here are some DIY steps to identifying and repairing fireplace mortar cracks:

1. Clear the area around the fireplace and chimney where cracks are identified.  Debris too close to the fireplace could cause a fire. Check the flue and firebox for obstructions like a clump of leaves, excess soot that may be hiding cracks.  Brush all mortar joints to examine them for broken pieces or damage.
2. Prepare New Mortar.  Purchase a mortar package that is specifically designed for use in fireplaces and follow the directions to prepare your new mortar.
3. Apply Mortar to any visible cracks. Use a masonry trowel to fill in any gaps you see in your brick joints.  Push the loaded trowel across the area and push the mortar into the cracks and fill it completely. Repeat this as needed until the cracks are entirely filled with new mortar.
4. Remove Excess Mortar. Use a damp cloth to remove any excess mortar you applied.
5. Smooth Mortar Surface.  Wear safety gloves and smooth the surface of the repair with your hands.  Push the mortar more deeply into the cracks for a tight seal.
6. Allow 1 to 2 days for drying completely.
7. Clean Up Debris.  Make sure your firebox is completely clear of debris and supplies prior to starting a new fire.

Missing Flue Tile Mortar Joints:  Either the flue mortar joints were never installed properly or they have possibly eroded over time due to rain water dripping down the chimney.  If your tile joints have gaps between them, they need to be filled with mortar because smoke can leak out the sides and cause a fire hazard.  Especially if you notice black stains around the flue tile, this is a huge red flag that a fire could occur because the chimney is not drafting properly.  Your sweep can identify and repair these for you, call them before using your fireplace again.