How to Repair Cracks in Cementitious Fireproofing

Updated February 21, 2017

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.

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.

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

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.

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.

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


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.

Things You'll Need

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

Residing in the coastal county of Devon, England, Jane Humphries has been writing since 2004. Writing for "British Mensa" nationally and regionally, Humphries has also held key roles within the High IQ Society. She received a Bachelor of Science, honors, in psychology with combined studies covering biology, statistics, economics, politics and sociology.