Advice on timings please

[Hesaweapon]

I have built my dome and entrance using firebricks and home brew mortar. Finished that today.
I used a sand form covered in paper. When can I remove the sand?
How long do I need to wait before doing the vermiculite layer (my choice for insulation) ?
and then how long before adding final layer of external render / mosaic tiles?
I'm eager to get it finished, but don't want to rush it if there's a reason to take things slowly.
Do I begin to slowly heat the oven to cure it once all layers are complete, or is this step supposed to come before then?
thanks for any advice on timings

[david s]

For a brick build, one of the major drawbacks using a sand form is the inability to tidy up internal mortar courses as the dome build progresses. You don't give the oven size so there may be some variability in the access to tidy up internal joints. Given that you used the homebrew mortar which requires a minimum of 7 days damp curing, the dome should be kept damp for at least this length of time. Also you don't mention whether the fire bricks were moistened before laying, your location and therefore your climate, as well as current weather conditions. Removal of the sand mould as soon as the dome is finished is probably the best procedure as the dome is self supporting and the quicker internal joints are tidied and filled, the better the bond and as well as their extended damp curing requirement.The dome should be covered during this time to hold in moisture present which allows the hydration process to do its job. After sufficient hydration via damp curing the dome should be allowed to dry. A week of sun and wind will do this job nicely (weather dependant).

From your initial description I understand you are not using a ceramic blanket insulation layer, but rather going straight to a vermicrete insulation. This does present problems in that the greater flexibilty of ceramic fibre blanket does provide a nice expansion joint. Applying vermicrete directly to the brick dome, as well as being less flexible than blanket, adds loads of water to this area, rather than blanket which is dry. Unfortunately moisture locked deep in a vermicrete layer, especially one sitting against the hot inner dome, can create problems with steam build up right in the place that you don't want. I learnt by experience when I began building ovens, with oven 2 and 3 both suffering cracked external shells. In the days before the modern ceramic fibre blanket, which has been exonerated as a Class 2 carcinogen, (Morgan Superwool being one), I relied on vermicrete/perlcrete as the sole insulation layer. I concluded that the moisture locked deep in the 75mm layer, against the inner dome was the culprit. A thick vermicrete layer will swell considerably from expanding steam. Altering the build regime to do the vermicrete in two layers with a week of drying in the sun and wind after each layer, prior to any drying fires, fixed the problem. I now use blanket layer(s) followed by a layer of lean (10:1) verm/perlcrete, which reduces drying times, speeding up the build process,
Builders opinions vary regarding the drying (curing) fires. I believe they are best done after the vermicrete has dried, but before any render coats are applied. This then allows a far better opportunity for moisture to escape to the atmosphere rather than being trapped in by the render layers. The 7 fires, getting progressively bigger, in 7 days is the usual method.

Hope this helps. Your location, weather conditions, oven size and perhaps a few photos might explain your situation better.