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 www.csia.org.