Homebrew castable build, Newcastle UK

[Mullster]

As always, awesome information DavidS andGulf - really helpful.

As I said - UK guys that find good materials (valves, caps, etc) for achieving this please share the info.

[mesoiam]

Thanks all, some good detail on this thread

[Gulf]

Here is an old cross section of my oven.

[david s]

Around a decade ago we received a new kiln at the school where i was teaching and it required firing to service temperature (1180 C), empty apart from kiln furniture. I was surprised to see at 400C (750F) water dripping from the front righthand bottom corner of the kiln making a puddle of around 100 ml on the floor. I was surprised that this was happening at such a high temperature. I surmised that the water was being pushed out of the insulating firebricks condensing on the inside of the cooler outer casing and running down to exit at the bottom.

So perhaps a 4th alternative would be to make a few weep holes near the base of the dome, but higher than at the slab level, so water won't enter there. This could be a good location because as the top of the dome dries out first and steam gets driven out to hit the inside of the cooler outer shell where it condenses then falls down, the wettest part is going to be at the base of the dome. Steam pressure from the top of the insulation space in this case will act to force moisture to exit at the lower vent holes.

[david s]

The vent acts like the hole in a saucepan lid to relieve steam pressure build up in the insulation layer. Water will always travel away from the heat source so first it leaves the inner dome then sits in the insulation space. An exit path via weep holes under the floor insulation as well as one higher in the dome allows it to exit the oven. Without them the oven will eventually dry, but why not provide an easier exit so the oven can get back to efficient operation far quicker?
Here are three different solutions: 1. a vent at the apex of the dome, like Gulf's oven. 2. a vent incorporated around the flue pipe like my system. 3. a vent that uses the flue pipe as the exit path.

[mesoiam]

Just for the insulation I would say Mullster, for when the water rapidly boils off but would otherwise be trapped by the render.

[Mullster]

Also if anyone finds a product in the UK similar to what Utah is showing please share. My research is throwing up some different looking air filter type things!

[Mullster]

Daft question coming up - these vents / breather vents - where do they go through to? Are we talking about creating a hole in the castable dome? Or just the insulation layers? Creating a hole in the dome feels so counterintuitive.

[mesoiam]

Not so much tiles but 4 or 5 rings around the whole thing. The holes would be poked before it sets, rather than drilled.

[Nick J C]

Hi Russel, would you consider the pressure to build up under the vcrete or under the final render? I was going to leave the final coating until after the curing fires, then do a ridged final render with perforations under the lip, See sketch. I was thinking the vcrete would be porous enough to let vapour through with the risk being created by the final render being a seal. What's your thoughts on that?
Thanks

Wow, that seems complicated.... Are you going to going to do multiple ridges to look like tiles, then drill the holes when cured? Would be a novel, pretty solution. I am heading towards putting a gazebo style roof over mine, with a single vent in the dome - probably copper pipe flush with the apex and a removable bung.

[mesoiam]

Cheers, the splitting was due to me being heavy handed with the removal of the flue gallery mould. I should not have hammered it when the castable was still quite fresh. My mould was a bit half baked to be honest. It was a shaped wooden cap to form the funnel, and then just filled in with sand below, if I was doing it again properly I'd think it through a bit better to consider the demould strategy. Make sure the homebrew cannot curl around and lock the mould in place at any points, make sure screws are accessible for removal, and dont make any parts thinner than they should be

[WoodywWun]

Mesoiam, Thanks for the many detailed posts and your problem-solving journey. It has all been very informative and helpful. Just going back to your splitting issue, when you de-moulded, was there a moment during the time leading up to this when the home-brew was in a sort of mid-curing condition that you might have been able to scrape back any potential parts of the homebrew that might have caught later on? Or maybe these weren't accessible? Was there any part of your mould that (chimney support area?) that might have been kept as a separate part and removed early when the home-brew hadn't cured fully?

I'm just coming up to casting so any guidance or ideas would be great. The oven is looking great!

[mesoiam]

Hi Russel, would you consider the pressure to build up under the vcrete or under the final render? I was going to leave the final coating until after the curing fires, then do a ridged final render with perforations under the lip, See sketch. I was thinking the vcrete would be porous enough to let vapour through with the risk being created by the final render being a seal. What's your thoughts on that?
Thanks

[UtahBeehiver]

Now is the time to consider a breather vent in the apex of the dome before the final decorative coating. This allow any water that sublimates to steam to vent without building up pressure under the vcrete..Liquid water volume expand 1500 time when it converts to steam. Cheap insurance. There are many ways to accomplish, Gulf and I use breather vents from any auto store, less than $10 with a 1/2" pvc bushing set in the render.

[mesoiam]

Thanks folks. I have drilled some concrete screws into the top of my pillars, the wire wraps around these. There is also a ring of wire around the flue, the upper ones of the decorative arch also go and hook around this, the wire gets hidden by the vermicrete at the end.