Hearthstone Question

I haven't found anything like that

Neither have I, but I haven't seperated the flue to look niether

I seem to recall reading something similar about this in the past. I think the consensus was that it was nothing to worry about. I very vaguely remember Highbeam being in on the conversation (although I could be mistaken), you might want to ask him if he knows anything about this.

There will be lots of extra cement that will be found falling off inside the hearthstones. Seems they goop up the blocks (and everything else) and push them together during construction, spooging the extra into the stove and only cleaning off the outside. In addition to the cement, there are also steel biscuits set in grooves between the stones. So long as it is only the extra spooge falling off and not the actual cement from between the stones then you are fine.

A very liberal application of cement goes into each hearthstone which means that it will spall off over time. I still get chunks every now and then but I have never gotten a single 15" piece. Mine are usually 4 inches or less. Also, the cement in the visible part of the firebox has been smeared kinda flat for looks. The smeared cement will actually bubble up into hollow bubbles that will eventually "pop" and you can kinda chip the crater smooth.

Despite loosing the cement, I haven't had a leak from the outside of the stove. My only leaks have been with the secondary air manifold that is cast iron and assembled without gaskets. Those leaks are easy to identify as jets of flame. Easily fixed with furnace cement.