How to Repair Cracks in Cementitious Fireproofing

Written by jane humphries
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How to Repair Cracks in Cementitious Fireproofing
Fireproofing maintenance is important to prevent a house fire. (fireplace image by askthegeek from

Cementitious fireproofing is a refractory cement product used to contain and reflect heat from fire. The most commonly used application is for firebrick installation within a fireplace. Over time the cement develops cracks. These cracks must be repaired with the correct cement to prevent heat and gases from escaping. The temperature of a fireplace reaches up to 816 degrees Celsius, so it is critical to regularly check and repair cementitious fireproofing to protect your home.

Skill level:

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Things you need

  • Fireplace shovel
  • Fireplace brush
  • Hand brush
  • Scrubbing brush
  • Water
  • Measuring tape
  • Fire cement
  • Putty knife

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  1. 1

    Clean the fireplace of all ash and debris using a fireplace shovel and brush. Sweep the cementitious fireproofing from the top to the bottom to remove soot. Use a hand brush to sweep the fireproofing cracks to remove loose cement.

  2. 2

    Wash the cement fireproofing cracks and surrounding bricks clean, using a scrubbing brush and water. Allow the fireproofing to dry.

  3. 3

    Measure any cracks between fireproofing bricks, using a tape measure, to determine whether to replace or reset the bricks rather than just repair the fireproofing. Replace or reset any bricks with joint cracks more than 1/4 inch wide, to reduce the joint width and provide effective fireproofing.

  4. 4

    Use fire cement with a rating to withstand temperatures of up to 0-5.556 degrees Celsius. Apply the fire cement to the cement cracks using a putty knife. Push the fire cement into the cracks and slightly overlap the joint to each side.

  5. 5

    Allow the fire cement to dry and cure according to the manufacturer's instructions before using the fireplace.

Tips and warnings

  • Call a local fire safety officer if you see cracks in the main firewall in the fireplace. You must determine whether there is a structural problem with the chimney or chimney foundation.

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