Repairing small cracks

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Yay!!! In light of your patience factor <grin> you may find it
cracking. Despair not. Just get a tube of Furnace Cement (not mortar).
It comes in tubs or caulking tubes...the tube is perfect.

Ignore the instructions and pop a fire in the oven. This will open up
the crack a bit. Then go through with your caulking gun and apply the
cement to the crack. Be generous. You need heat to set it and since
the outside doesn't get very hot, you need to have a fire going inside
to open the crack and to get the cement hot enough to set. If it's a
pesky crack and you need to reapply, grind a slight groove with an
angle grinder along the crack or use a church-key or screwdriver to
groove it a bit before going the cement route.

Once the cement has a chance to cure it's as good (maybe better) as
new. Furnace cement has a 2000F temp rating (which is why you want it
& not the furnace mortar).

Jim