Small hair line cracks in fireplace

Last Edited By Krjb Donovan
Last Updated: Mar 13, 2014 03:11 PM GMT


I have a mason brick fireplace that is over 30 years old. I have two small cracks in two bricks. I was told that I can fix it with mill pack. The big problem is that the mill pack comes in 50 pound bags. What else can I use that would withstand heat of 1200 degrees? The cracks are less that 1/4 inch wide. It goes from the top of the brick to the botton of the brick.


Do NOT try to use Mill-Pack. It is NOT the correct material for repairing a masonry fireplace.

You should use a refractory cement of some sort. A refractory cement in a caulking tube is often used by our technicians.

The joint must be clean and dust-free. Apply the materials to the area of repair, pushing the materials FULLY into the joint. Let the repair dry for 48 hours before using the fireplace again.

Alternatively, I recommend you contact a local CSIA Certified Chimney Sweep to do some on-site diagnosis of your problem. THey will typically carry this repair material on their truck.

You can find a CSIA Certified Chimney Sweep at


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