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Black Fireplace Mortar

Not for exterior use. Apply 1/16 - 1/8 inches thick!

Fireplace Mortar Black

List price: $15.99  
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Keep your indoor fireplace or insert in tip-top shape with our 10.3 Fluid Ounce Black Fireplace Mortar in a convenient caulking cartridge that holds enough to cover up to 99 feet! It's perfect for filling in those little holes, cracks, and imperfections that tend to occur between the bricks and masonry on your fireplace--or for any fireplace mortar repair! This heat-resistant mortar can be fired immediately after application. Once properly cured at 1200°F, it will withstand temperatures up to 2000°F and will be as hard as the surrounding firebrick, giving you to complete assurance that this is a quality product made to last! While the black color will match many fireplaces, this mortar can be painted any shade after curing to ensure a perfect match. We recommend using only on areas 1/8" or smaller. Meets ASTM E-136 and E72 non-combustibility standards.

Remember to check out our "Silicone & Caulking Tips: DIY like a Pro!" below to see if we have any suggestions to help make your DIY project easier. If you have any questions, we’re happy to help! Give Fast Replacement Glass a call at 1-888-986-1535, start a live chat, or email us at [email protected].

Size: 10.3 fl oz cartridge
Color: Black
Temperature Rating: 2000°F (1093°C)
Certification: ASTM E-36 and E72 non-combustibility standards


  • To use:
    • Burn a low fire to dry the fireplace mortar.
    • Heat under extreme heat to cure.
    • This mortar is rated for indoor use only. 
    • For large repairs (exceeding 1/8" areas), a castable refractory cement is highly recommended.

How to caulk like  pro!Silicone & Caulking Tips: DIY like a Pro!

  1. Product cartridge fits into a standard caulking gun. For clean application, cut the cartridge tip near the end, at an approximate 45° angle.
  2. Ensure that the working surface is clean, dry, and free of debris. Have some damp cloths or a roll of paper towels within reach. Lay down newspaper to protect carpet/flooring from possible drips.
  3. To lay a professional bead, hold the caulking gun at 45°. Spin the cartridge tube so the longest part of your tip is aligned with the top side of the caulking gun.
  4. Beginning at the highest point of your working area, slowly and gently squeeze the trigger and drag the gun to lay an even bead (about 1/8"). 
  5. For a clean job, remember that "a little goes a long way!" Try to be consistent when laying a bead - you can always go back and add more material later.
  6. As you near the end of the working area, release the trigger (or press the release lever) to stop the flow of material.
  7. After applying the material, let it cure for the indicated amount of time (at room temperature) before using your appliance.


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Last updated on November 28th 2017.