48” Naples style oven in Edmonton

[beefborley]

To give you a K value (thermal conductivity) comparison, ceramic blanket has a K value of about 0.50-55 where as the Kastolite 50-25 K value is 2.23 meaning it will transmit heat over 4 times more than ceramic blanket. So it is your call.

In that case I still have space to add an inch or two of ceramic blanket on the exterior of the castable.

[beefborley]

Good job, That looks like a pretty good solution.

Thanks David, I will report back as I progress.

[beefborley]

Does either the Kastolite 23 or 50-25 look more suitable? Should I prioritize the lower conductivity of the 23 or the higher strength of the 50?

[david s]

Does either the Kastolite 23 or 50-25 look more suitable? Should I prioritize the lower conductivity of the 23 or the higher strength of the 50?

That's a difficult question. If it were mine I'd be choosing around a 5:1 vermicrete which has a strength of around 200 psi. Either of the two Kastolite products are an overkill IMO because ithey use calcium aluminate cement to give them a far higher temperature rating than you require, it will also be way more expensive than a mix you make up yourself. At the temperatures we fire to a vermicrete mix is perfectly adequate. The Kastolite 50-25 is far denser, with greater strength, but poorer thermal conductivity, although if you are using blanket insulation outside it, maybe there'd be little difference.
The table you posted is difficult to read and there are lots of different units used, so comparisons are not easy.
Here's a resource that might help you.

https://www.vermiculite.org/wp-conte...e-Concrete.pdf

[beefborley]

That's a difficult question. If it were mine I'd be choosing around a 5:1 vermicrete which has a strength of around 200 psi. Either of the two Kastolite products are an overkill IMO because ithey use calcium aluminate cement to give them a far higher temperature rating than you require, it will also be way more expensive than a mix you make up yourself. At the temperatures we fire to a vermicrete mix is perfectly adequate. The Kastolite 50-25 is far denser, with greater strength, but poorer thermal conductivity, although if you are using blanket insulation outside it, maybe there'd be little difference.
The table you posted is difficult to read and there are lots of different units used, so comparisons are not easy.
Here's a resource that might help you.

https://www.vermiculite.org/wp-conte...e-Concrete.pdf

Thanks for the advice. I will likely just use a vermicrete mix then. I’ve seen recommendations for a 50/50 mix of vermiculite and perlite. Would that be recommended for this application? If so, it would be 2.5 vermiculite: 2.5 perlite: 1 Portland cement? Is there any sand used in the recipe. See attached pics for form prepped for casting. I will strap the top of the form prior to pouring.

[UtahBeehiver]

I would agree what David S said in his last post on a 5 to 1 ratio. Also, "no sand" which dramatically reduces K value.

[beefborley]

I “poured” the vermicrete layer yesterday. That is weird stuff. Feels like casting with kitty litter . It feels surprisingly solid today though. Time to finish the dome.

[beefborley]

I believe that I will run out of Heatstop mortar with a couple of chains to go on the dome, and don’t think that I will be able to order anymore. Will the home brew mortar be strong enough, and heat resistant enough for a commercial application that is constantly being fired, or should I be looking to make a calcium aluminate mortar?

[beefborley]

I finished the dome and removed my styrofoam forms. There are definitely some mortar gaps in the interior that I will climb inside and attempt to fill and clean up, but everything feels quite solid.

I am planning to build a squirrel tail vent to bring the chimney back towards the center of the oven. Should I insulate between this vent and the top of the oven, or can this venting be constructed directly on top of the firebrick? If I can build directly on top of the dome, I will likely use firebrick or possibly cast with refractory.

[NCMan]

I've never built one like that, but every one I've seen done were built right on top of the dome and then insulated over the whole thing.