Homebrew castable build, Newcastle UK

[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]

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

[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.

[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!

[mesoiam]

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

[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.

[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.

[Gulf]

Here is an old cross section of my oven.

[mesoiam]

Thanks all, some good detail on this thread

[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.

[Hattori-Hanzo]

I'm starting to think about this stage myself and read a post where copper tube was inset into the render that pasted through to the ceramic blanket layer. The copper tube was then bent over slightly to stop rain getting in.

Is this still a viable method as it seems the most simple?

It was suggested that one copper tube near the top of the dome would suffice but could I also add some near the bottom as David suggests to help moisture release further?

[Gulf]

......The copper tube was then bent over slightly to stop rain getting in.....Is this still a viable method as it seems the most simple?.....

It is in my opinion. That was the first design that I saw. I believe that cobblerdave did this. I like any threaded design that allows the vent to be removed and plugged once the oven is dry. It's not necessary to remove it, but some don't like the look of it there all the time.

[UtahBeehiver]

In the UK it is called a Breather Valve, all types, bottom line you want something that lets the moisture out but not let the rain or water in.

[sergetania]

Does that breather valve need to be itself protected from the elements? Will rain, oxidation, dust mess up its ability to release moisture? Thanks!

[Alomran]

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

Try https://www.ebay.co.uk/i/29276960597...CABEgKTjfD_BwE
or
https://www.ebay.co.uk/i/12263131235...iABEgJLB_D_BwE

or
https://www.ebay.co.uk/i/15201330389...SABEgK1ifD_BwE

or https://www.ebay.co.uk/i/33332646255...CABEgKSM_D_BwE

or https://www.ebay.co.uk/p/248565222?i...SABEgL3MfD_BwE

City plumbing has
http://www.flowfitonline.com/mintor-...CABEgJDEvD_BwE
& https://www.cityplumbing.co.uk/Kings...?gmcpid=994214
there few models in https://www.flowfitonline.com/search...&name=MA01.pdf

If not available you can get the smaller one for a motor Harley's !!
https://www.ebay.co.uk/itm/Motorcycl...sAAOSwD5teLqnV


You can buy any trailer's fuel or oi tank valve.

For all the aforementioned, you are advised to contact the seller to ensure that the valve is

1- Metalic
2- the valve is a one-way valve allowing air out (BUT NOT IN).

You can search for any odd truck's fuel vent valve
I got a bus's fuel tank valve for my oven!

good luck
Mustafa