Bricks moved during laying of keystone problem

[Cameroonian Kid]

Ive just completed my ninth chain. I had some droop, and was trying to rectify it over the next few chains....

Unfortunately, as I was laying the last brick on the ninth chain, the previous three or four bricks that I layed, moved a bit ( maybe 1/4 inch in towards the centre of the dome). Is this a problem? They seem relatively stable. I think part of the problem is that two of the bricks are " floating " on their internal edges ( see pic). This was to try and fix the droop.

So, can I fill this internal gap with mortar, or will mortar break free eventually? Should I leave it? Any help about these two issues would be appreciated.

Also, I've run out of my premix mortar. Can I make some home brew out of dried brick " dust/slurry" ( instead of fire lay)?Is it a problem having two different types of mortar in the one pizza oven build?

Thanks

[dakzaag]

You have probably moved on by now and whatever you did is fine. For any future readers, here is my philosophy on the condition that you posted. Since you noticed the problem before laying a bunch of brick on top of these "swimmers" then the best thing to do would be to relay them and get them in the proper position. If you had closed in the top and just noticed the gap, well then I would just leave the brick alone and point some mortar in the gap.
As the dome fills in, the brick are increasingly suspended in mid air and rely completely on the sticky mortar to hold them in place. This becomes a feat of magic, defying gravity and I usually finish the dome with a small sand pile built up on a disc of plywood that I position inside the last ring that is laid. I support the plywood disc with brick or whatever stacked up from the oven floor. At this point, the IT has become a Dispensable Tool because the sand form now takes over as your guide for laying the brick. Damp sand, firmly packed and even covered with wet newspaper will hold the brick in place until the oven is closed in and the natural strength of a dome resists the collapsing forces of gravity. If you are cutting the brick perfectly with no gaps at all, then it is possible to close the dome without some support, but you have to go slow and allow some time between chains to let things set up a bit.
The down side of a dome support form of any kind is that you cannot see how well you are laying the brick next to the previous brick and inevitably you get gaps and lips in the ceiling of the dome because you are laying them blind. If the support is absolutely perfect and rigid enough resist pressure then the inside would be perfect, but finding the right shape or making a ball out of common construction materials is not easy. Some builders use 2" Foam Board and if you take enough time to cut it just right and have enough of them to support most of the brick, then you can get a really clean interior. Just remember that this is mostly cosmetic in necessity and doesn't really affect the long term strength of the dome.
With regards to the second question, I believe that just about any potters clay would work with the home brew instead of fire clay. Most pottery supply places have never heard of fire clay and most masonry supply chains haven't heard of it either. Some suitable substitutes that are more readily available are Heat Stop II or Flue Set which are both complete refractory mortars and just add water. For a home brew without Fire Clay, I would look for a pottery clay that is lighter in color if possible like a blond or yellow clay and use that as the fire clay. Actual fire clay is getting pretty hard to find at least for me and I have noticed that the refractory supply outlets are shying away from providing the stuff because people don't know how to use it and they want to sell a higher priced replacement mortar. I find the cost of Heat Stop II is lower when buying bags instead of small tubs and the convenience is really nice, just mix what you need for an hour or so at a time. If you're really trying to save money then the oven is probably not going to fire 5 times a week and the home brew is good enough for casual use.

[david s]

Some folk use 4 or 5 sticks to support the bricks (one per brick). By the time you're on to the 5 th brick you should be able to move the first one. Just use the IT to get the position of the brick then use the stick to support it.