Quick advice on sequencing

[lightsofroy]

Hi all, I’m hoping that somebody can help me with the timing of my next steps

My dome was finished today. Outer arch/ chimney stack tentatively planned for the coming weekend, weather permitting.

I plan on covering the dome in CFB and chicken wire, followed by an inch of vermicrete and an inch and a half of cement screed. And yes, I’ll have a breathing cap on there too!

My question is one of sequencing.

I’ve read that once I’ve done all of my brickwork, I walk away for a week and let it do it’s thing before returning to start the curing fires.

Do I complete my vermicrete layer BEFORE walking away for a week or do I leave it for a week, cover with the blanket, then cure, then come back and do the vermicrete?

I know I should do my final render afterwards but I realised earlier that I wasn’t totally clear on how to accommodate the vermicrete step.

My gut tells me I should do CFB, vermicrete, THEN walk away for a week but my gut has caused me to do some silly things in my life!

Appreciate any pointers anybody can offer

Thanks

Alex

[UtahBeehiver]

Insulate the dome with the ceramic blanket "before" any curing fires are started. The insulation tempers the temperature differential between the inner and out dome surface, minimizing the potential of cracking. The vcrete is not necessary to complete before curing. I would start with a couple briquette fires before wood. Then when you go to wood be really careful with the load. One extra piece of wood will dramatically spike the temp and could crack you oven.

[lightsofroy]

that's great, thanks Russell. the weather forecast was starting to look a little grim so I decided to get straight on with insulating as soon as I finished the landing. So, blankets are on, vermicrete is on. Will leave a few days before starting the slow process of curing!

[JoJoMojo]

I had my dome crack. i cured wayy too soon and to high of heat. I was able to put fire mortar on the craks, due to the fact that i had not laid on the insulation. I did not cure again unitl 2 weeks after the last brick was laid and the front arch and vent was complete. then i did curing fires over too weeks, super slow. kinda scared to damage it futher.
I have had no issue with the functionality of the oven, or from the cracks from prior to laying insulation and completing the dome.
I did have my outer dome crack slightly on both sides of the oven at the bends points of the arch.
I painted my stucco with a waterproof outdoor sealant and the cracks have not taken on any water or show signs of being an issue.
I dont know if this hurt my longevity of the oven, but it holds heat for 2.5 to 3 days.... and cooks amazing and draws well with no other cracks or issues forming.
HOpe this helps. ill upload a photo of the painted sections. you cant even tell they are there with the heavy duty exterior sealant

[david s]

I agree with Utah about driving out the water with the drying fires. It should be done after the oven has been insulated. The reason for this is the enormous temperature difference between the inner and outer surfaces which set up a huge difference in thermal expansion. Insulating the outer surface allows a much slower and even penetration of heat into the material (brick or refractory). This is best illustrated by the video of an uninsulated flue tile being heated internally with fire, Granted an oven is way thicker and not subjected to such extreme differences in thermal expansion, but the same principle applies and is borne out not only by your example , but of many others who have cracked their ovens doing the drying fires on uninsulated ovens.

https://www.youtube.com/watch?v=lUFax3YsVm8

Regarding the cracks in the outer render or stucco layer, they don't matter that much as it is really only a weatherproof layer and to hold the insulation in place. However, even a small crack is an entry point for water to get into the insulation reducing its ability to do its job. The fine cracks should be filled for this reason.