I have an interior chimney 25 foot with 8x8 clay flue interior is 7x7. And where the stove connects they used a terra cotta crock (thimble) the section of clay flue were the thimble connects is cracked. The rest of the chimney is in good condition the top 8 feet was rebuilt 5 years ago. In between each section of terra cotta flue is about 1/2 inch of cement. I was talking to a mason and he said he could break and chisel out the broken piece of flue and replace with a new section. Is this possible ?