Homebrew cast oven UK Build

[columbiers]

Sand former removed after 2 days. All seems solid enough, needles all embedded well. Few pieces of newspaper stuck inside but these will burn off. Going to need more sweeping out as the sand is everywhere in there!
Twin wall stainless steel flue arrived, test fitted as an interference fit, nice and solid fit. Going to use fire cement from Flomasta to bed it in next, with a first small fire to cure the fire cement. Probably wait a few more days to do that. Then a perlite insulation layer over the dome going around the flue. Hoping another 3 weeks or so till the first pizza comes out.

[david s]

Great job. Just be a bit careful about embedding the base of the flue pipe with dense material. I did just that with my second and third ovens and the more conductive stainless pipe expanded first and cracked the casting surrounding it. As this happened to both ovens I concluded it wasn’t just an anomaly. I now make it a loose fit and surround it with 8:1 vermicrete which won’t effect the casting and which has some elasticity. You can wrap some corrugated cardboard around the flue pipe then pack up against that with the dense material and when it has set remove the pipe and discard the cardboard. This will give you a slightly loose fit. You can then pack around the pipe going up about 200 mm with the weaker vermicrete mix to support it.

[columbiers]

Thanks David, I'm going to take your advice and just fit the chimney in. It fits fairly nicely now so I won't add any cement or more castable. I'll just build up the perlite mix round it by 200mm and then render up to it later.
I will be fitting a roof later now so that will give extra support to the chimney too.

[columbiers]

Insulation layer added today, perlite at 9:1. Basically just slapped it onto a depth of 5cm and then smoothed it over. Didn't overdo finishing it because it will be rendered soon, 2 layers, that will smooth it out Chimney fitted, just fixed with the perlite mix as per advice above
Plan is to leave it for a few days and then begin small fires to drive out the water slowly.

[david s]

Don’t be in too much of a rush. There is so much free water left in the vermicrete layer it is best to wait at least a week and let the sun and wind do a lot of the drying for you. Hopefully the weather will be kind to you. Obviously cover it to prevent rain though. If you see steam during the firing ,back off, you’re going at it too hard. Read the curing thread starting here https://community.fornobravo.com/for...curing#post833

[columbiers]

Will do, we're forecast sun all week here so that should get it well on the way

[columbiers]

After consideration added another layer of perlite for extra insulation. Left for 7 days to dry out.
Now begun a series of fires. Started with walls at 30 degrees, went to 60 today, looking to double to 120 tomorrow. Chimney has a good draw so far. No sign of cracks inside, the homebrew as castable is my one area of deviation from the 'norm' and is looking to have worked well so far. Aiming for a full temp fire on Friday,followed by rendering of dome

[david s]

After consideration added another layer of perlite for extra insulation. Left for 7 days to dry out.
Now begun a series of fires. Started with walls at 30 degrees, went to 60 today, looking to double to 120 tomorrow. Chimney has a good draw so far. No sign of cracks inside, the homebrew as castable is my one area of deviation from the 'norm' and is looking to have worked well so far. Aiming for a full temp fire on Friday,followed by rendering of dome

You don’t say how thick the second layer of vermicrete is but as the first was 50 mm thick i’d Guarantee that the inner layer against the dome will still be fairly wet after one week. Because it is the equivalent of throwing a thick layer of wet towels over the oven which you wouldn’t expect to be dry in one week. If you can purchase a cheap moisture meter and plunge it into the vermicrete until it touches the inner dome. Although the vermicrete will appear dry on the surface the meter will tell you how dry it is deeper. Before the new generation of blanket became mainstream, safe and cheaper, I used to always only use vermicrete as the insulation layer. Drying it became too tricky and I found it much better to do it in layers of about one and a half inches with a weeks drying in between. Getting too enthusiastic about finishing at this stage is risky. Good luck.