32” cast oven in Warwickshire

[Badbobby]

@ David S - can you confirm how long i need to leave the insulation verm layer to cure prior to running the week of fires? To clarify, the homebrew cast dome had a week of wet curing and it's about a month or so in total since i first cast it.

My hope, based around a 2 week holiday i have booked on 12th August, is that i can leave it a week and then get on with starting fires before i go away. Ready to have pizza on my return!

[david s]

Because you’re not after strength in the vermicrete layer, it only needs to be firm enough to apply the stucco/render on to. The more cement you add to it the more you reduce its insulating capacity. Because the mix takes up so much water ther is a lot of free water in it so I see no need to damp cure. It is eliminating this free water that’s a more important issue, so I give it a week of drying in the sun and wind, keep off any rain.

[Badbobby]

Because you’re not after strength in the vermicrete layer, it only needs to be firm enough to apply the stucco/render on to. The more cement you add to it the more you reduce its insulating capacity. Because the mix takes up so much water ther is a lot of free water in it so I see no need to damp cure. It is eliminating this free water that’s a more important issue, so I give it a week of drying in the sun and wind, keep off any rain.

Thanks David.

I was wondering whether the verm layer is more prone to cracking etc from the heat via the cast dome. Shame it's raining a lot in the UK! Sounds like i can start the fires this weekend. Very excited!!

[Badbobby]

Congratulations - that's a really nice looking build. I am also at the slow cure stage of my build which I started after a roughly 10 day moist cure of the dome and flue. From what I can gather, holding in the moisture for at least 7 days (I went with Dave's advice of wrapping in cling film) will increase the final compressive strength of the mix versus a dry cure but in any case the cement will reach its final compressive strength after 28 days. My vermicrete was only a few days old when I started the curing fires but by the time it see's any significant heat from the dome it will be at least a week old.

Having said all that, I do now wonder if a higher compressive strength increases or decreases the risk of thermal cracking. There's virtually no structural load on the homebrew domes, so does a stronger compressive strength help or hinder when it comes to thermal cracks? Any experts out there?

Thanks for the comments. I see you’re enjoying it so much that you’re building a second. I have a feeling I’ll be “consulting” (doing) on others for my friends next year…

[david s]

It will crack a bit from expanding steam pressure, so that's why a week of sun and wind is preferred.If applied over blanket then the blanket acts as an expansion joint which lessens the problem. Even if it cracks a bit it doesn't matter because it will be held inlace between the inner and outer shells.

[Badbobby]

If anyone wants to pick up some excess materials, I have the following:

- 12 fire bricks
- 1.5 rolls of 25mm fibre insulation
- most of a large box of stainless steel needles
- burn out fibres
- 25kg bag of clay

Just let me know and I’m sure I can agree a reasonable price. South of Coventry.

[rayturf]

Hi Badbobby. We're right at the beginning of our pizza oven build and have found your thread and instructions really helpful. At the moment we're trying to find materials and gather them ready to start the build. We're in Cheltenham, so not that far from you I think. Do you still have your excess materials left?

[Badbobby]

Hi Badbobby. We're right at the beginning of our pizza oven build and have found your thread and instructions really helpful. At the moment we're trying to find materials and gather them ready to start the build. We're in Cheltenham, so not that far from you I think. Do you still have your excess materials left?

I’m very sorry, I didn’t see this. I sold most of the bits piecemeal on eBay. The fire bricks is a pain as the minimum order is way more than you need! I have built a bbq area out of my excess though.

Update: I have started up the oven this week - a few smaller fires to drive out the moisture. But I’m very glad I put in the metal escape valve. Once it was up to temperature there was a huge amount of steam coming out and I assume that the mortar would have cracked otherwise.

i really would recommend putting in a valve.

Still needed to put on render top coat and paint…