Trying to hit 900F in my tall sorta-cob oven

[Rocko Bonaparte]

I haven't really ever gotten such an intense heat as others report with their own ovens. I just got the scratch stucco finished so it was about time to fire again, but for months now I've done some test fires and even made some pizza. I tend to top out at 450F for doing any kind of sustained cooking. I can get the surface of the bricks up to 700F or so for a little bit after contact with a good fire. I haven't counted the number of fires I've done, but I think I've gotten past ten now.

Some notes on my build. The botton insulating layer is about 1:6 cementerlite for 3.5" or so. The firebricks are levelled with a mixture of sand and perlite. I don't notice a change in temperature under the oven 3 hours after firing. I neglected to measure it properly while measuring everything else though. The first few levels of the walls are halved firebricks basically mortared in place with thick wads of cob made from pottery sand and fireclay. The rest of the dome is made from that cob mix. It is insulated with 2" of mineral wool and then at least another 2" of 1:8 cementerlite; the thickness varies on the part of the oven you're looking at. At this point, I also don't notice a change in temperature on the exterior of the even, except for maybe right near the mouth or the flue.

The one trick is that the oven is taller than normal because I wanted to do more conventional stuff in it too. Specifically, I wanted to be able to get dutch ovens in and out of it. So the mouth of my oven is larger. The oven has about a 36" inner diameter and almost goes up rather largely--20 inches. I had factored compaction and settling that didn't happen so it might even be a few inches taller. The doorway is somewhere around 14 inches; it's 2/3 the estimated height for what I wanted for the even ceiling. I imagine this is causing a lot of heat to escape.

I haven't yet built a door for the oven, so I wonder if after the main fire is complete, if dooring it would probably take care of things. I don't see any mentions of closing off the oven to build up the temperature from others, but I wonder in my particular situation if something like that is necessary.