First time 41" clay/homebrew oven.

[sandybits]

Re: First time 41" clay/homebrew oven.

The golden mean is taken from flue exit to dome height, so........you are at 55%, itll still work.

Hey brickie, my calcs say 65% but I'm probably confusing my terms and definitions here. My flue sits inside my dome, as you mentioned, and where the flue opens up is is 310mm from the hearth. So where the smoke turns up from inside the dome to head straight up is 310mm.

However the door opening height is 55% of the dome height. This would seem to ignore the flue.

Just trying to understand

Thanks for the help.

[david s]

Re: First time 41" clay/homebrew oven.

Hey brickie, my calcs say 65% but I'm probably confusing my terms and definitions here. My flue sits inside my dome, as you mentioned, and where the flue opens up is is 310mm from the hearth. So where the smoke turns up from inside the dome to head straight up is 310mm.

However the door opening height is 55% of the dome height. This would seem to ignore the flue.

Just trying to understand

Thanks for the help.

That will still work ok, to cook pizza if you maintain an active fire on the side, but if you want to do retained heat roasting or baking (with fire removed) you will need a damper. Without one you will lose heat out of the flue and as soon as you open the door cold air will rush in and the hot air from the oven will all escape skywards.

[cobblerdave]

Re: First time 41" clay/homebrew oven.

Gudday
So in the meantime slide a piece of tile over the pipe till you find someone to fabricate a truck exhurst flap, chain thingy and enjoy you oven
Regards dave

[sandybits]

Re: First time 41" clay/homebrew oven.

Thanks guys. I will just chuck something up there until I can get a more permanent, efficient option.

On another note I was wondering how much heat can be lost out the very back end of the oven? I have posted a pic below showing the rear end of my oven. In an effort to get a bigger oven I ended up with my soldier course of pavers almost on the edge of the platform. I couldn't even get my thermal layer to stick as there was just nothing for it to sit on.

I can take the insulation layer right back down to the fibro above the brick base but it might get pretty thin around those pavers.

So the question is: if there is a weak point in your insulation, where it is particularly thin, will the heat try to escape there regardless of where it is? I guess water will leak out of a bucket no matter where the hole. Is that the same with heat?

Cheers.

[Greenman]

Re: First time 41" clay/homebrew oven.

Just my thought but I would expect that heat would leak more easily at the point of less insulation but I doubt that it would be the escape point to allow a mass exodus of heat from the oven.

I guess that the real answer is to load it up with insulation to the max in the first place.

[cobblerdave]

Re: First time 41" clay/homebrew oven.

Gudday
If there is not enough lip there to hold the thickness of insulation that you need put a strip of oiled wood there. Build your insulation on that you can remove it later and the insulation will stay in place
Regards dave

[sandybits]

Re: First time 41" clay/homebrew oven.

Just my thought but I would expect that heat would leak more easily at the point of less insulation but I doubt that it would be the escape point to allow a mass exodus of heat from the oven.

I guess that the real answer is to load it up with insulation to the max in the first place.

I tend to agree. If there is a heap of insulation in the first place, and its cheap anyway ("perlcrete"), then there is nothing to worry about

Gudday
If there is not enough lip there to hold the thickness of insulation that you need put a strip of oiled wood there. Build your insulation on that you can remove it later and the insulation will stay in place
Regards dave

Good idea. I was thinking of ways to add some brackets to the bricks to add something more permanent as I thought the insulation may be a weak brittle covering. However the oiled timber that could be removed would do the job anyway as there is no real traffic behind the oven to bump it anyway.


As to the next step, myself and my youngest are going to a rural buying store nearby to pick up a bag of perlite tomorrow ($23 for 100 litres). I might hook up the trailer and seek out some firewood at the same time.

[brickie in oz]

Re: First time 41" clay/homebrew oven.

myself and my youngest are going to a rural buying store nearby to pick up a bag of perlite tomorrow ($23 for 100 litres).

Thats a good price, for the same sized bag of vermiculite I pay around the $30 mark.

[sandybits]

Re: First time 41" clay/homebrew oven.

Thats a good price, for the same sized bag of vermiculite I pay around the $30 mark.

That was over the phone and for a medium grade (from memory) as I didn't know which one to use at the time (I still don't - hence why I just logged on). The vermiculite was more expensive, albeit only $3 more. So still slightly cheaper. I must be close to a mine

I just want to fire this thing up.

[david s]

Re: First time 41" clay/homebrew oven.

Get both perlite and vermiculite. As you want a weak mix that will insulate well, a 50/50 mix of vermicrete/perlite, 10:1 makes a more workable mix than either of them alone.

If you are not using blanket and the vermicrete is your only insulation then you need to make it around 100 mm thick. To assist it to dry do it in three or four layers with a week between each because for every 100 litres it will take around 30 L water and that's a lot to remove, especially if you cover it over with more.

[sandybits]

Re: First time 41" clay/homebrew oven.

Get both perlite and vermiculite. As you want a weak mix that will insulate well, a 50/50 mix of vermicrete/perlite, 10:1 makes a more workable mix than either of them alone.

If you are not using blanket and the vermicrete is your only insulation then you need to make it around 100 mm thick. To assist it to dry do it in three or four layers with a week between each because for every 100 litres it will take around 30 L water and that's a lot to remove, especially if you cover it over with more.

Thanks David. Is it best practice to cure the oven after all the vermicrete/perlcrete has gone off? Or do we just need to wait for the thermal layer to dry out? Or some combo of layering and curing? Also, is there any need to keep the insulation layer from binding to the thermal layer, like a blanket would? Cheers all.

[david s]

Re: First time 41" clay/homebrew oven.

Thanks David. Is it best practice to cure the oven after all the vermicrete/perlcrete has gone off? Or do we just need to wait for the thermal layer to dry out? Or some combo of layering and curing? Also, is there any need to keep the insulation layer from binding to the thermal layer, like a blanket would? Cheers all.

I prefer to do the curing fires after doing the vermicrete layers. Put the vermicrete directly on to your thermal layer. If you didn't add any burn out fibres to your mix you will have to go super slow to prevent steam explosions.

[sandybits]

Re: First time 41" clay/homebrew oven.

I prefer to do the curing fires after doing the vermicrete layers. Put the vermicrete directly on to your thermal layer. If you didn't add any burn out fibres to your mix you will have to go super slow to prevent steam explosions.

Burn out fibres. I missed that one. Is that sisal rope? Ahh, the first build. I'm learning so much.

Picked up a bag a vermiculite and perlite, 100 litre each. $49 all up. Should be more than I need.

As a bit of an aside I did some calculations to work out the surface area of my dome. Noone probably cares about this stuff but I thought I'd add it as its part of my build.

At the narrowest the radius of my dome is 570mm and at the biggest it is 635mm. That is measuring the inside and adding the pavers plus thermal layer. This gives me a surface area (after diving the result by 2 as its a dome not a sphere) of between 2.04 square metres (m2) and 2.53 m2. At 100mm thick insulation layer I need between 0.2 cubic metres (m3) and 0.25 m3. Or 200 litres to 250 litres of material.

At a 10 to 1 ratio (vermiculite/perlite to cement) I get between 0.19m3 and 0.23m3 of vermicultie/perlite and 0.02m3 of cement. A 20kg bag of cement is 0.01m3 or 10 litres so I need 2 bags of cement and probably all of the bags of 'lite. Lucky I grabbed 2

Now I've got to go and work out how to tell if the bags of cement I have in the shed have gone off or not.

Cheers.

[david s]

Re: First time 41" clay/homebrew oven.

You will lose about 20% of volume on mixing the vermiculite or perlite.

[brickie in oz]

Re: First time 41" clay/homebrew oven.

Now I've got to go and work out how to tell if the bags of cement I have in the shed have gone off or not.
.

Fore the price of a bag of cement just chuck it out and get a fresh bag.