Lower ground floor court yard

[HenrikK]

I'll put up a full report soon, but here's a teaser: pizza with pancetta, talegio and raddichio cooked in my oven

[david s]

That should be plenty, assuming your oven is to be a 28” diameter hemisphere. The cross sectional area of the flue is more important and powerful than the height in increasing the draw. The average height of most oven flues is around a metre.

[HenrikK]

Hi David,

I think it would be something like 28 inches and the flue pipe 133 mm so 5,5 inches. As lenght of chimney increases flow, what were the lenght used for those recommendations?

Cheers

[david s]

What size oven are you building Henrik?
For hemispherical ovens the following is a guide for oven flue diameter. For other oven types work on equivalent oven.volumes and for square or rectangular flues work on the same cross sectional area as the round flues.

up to 24" diam use 5" flue

24"- 39" use 6" flue

39+" use 8" flue

[HenrikK]

Hi Russell,

I'll put up a photo later that shows this better. To the right there is 2 metre wall to the next garden. The thick stone slab on theto of the lower wall through which the opening of the oven would sit ends to the right about 7-8 inches before the 2 metre wall. My thinking is to make the first bit of the chimney inside the lower wall ending centre between it and the higher wall. There I would put a 3 metre stainless pipe. Even if this gives quite a narrow chimney, the lenght should ensure a good flow.

Henrik

[UtahBeehiver]

After reviewing the pics again, I see what you are trying to accomplish. How are you going to install a chimney vent with this design if you need to replace the tiles back to original with the existing wall limiting your oven opening depth?

[HenrikK]

Great advice, thanks. Yes, indeed, it's starting to set, 36 hours after pour. But, you're right that drying out will be difficult. Maybe I'll fining the box and then make makeshift insulated lid and put a heater in it to dry it out.

[david s]

There will be no problem with the vermicrete setting. The problem will be eliminating the free water in the mix after it has set. The garden moisture meter will tell you when it is dry. When it flashes red you know it is dry enough.This post shows it’s use on insulation over the dome, but the same applies for under floor insulation.

https://community.fornobravo.com/for...695#post397695

[HenrikK]

I'm grateful for all advice. Part of the conditions for this build is that I promised my wife that things would look exactly the same afterwards, and that there are some beautiful old trees so I don't dare to make the hole in the ground too large.

I'm basically testing. If the perlcrete slab doesn't set, I would have to remove it and give up the ideas of insulating properties in the shell but just go for waterproof concrete and then insulate from the inside

[david s]

In that case don't use vermicrete or it may never dry in there, just use the cal sil board.
We just give advice based on our knowledge and experience here and that does not always mean we agree with each others opinions. I can't be sure that your plan won't work, but I am sceptical. I guess the only way to find out is to build it and report back, good luck.

[HenrikK]

David,

it's not an option to leave any open space around the oven. The agreement is that i must seal and put back the tiles afterwards so that the top looks like it did before I started.

deejayoh said above that i would have to build a waterproof concrete box and put the oven inside it. That's what I'm trying to do. As the ground provides structural support, I thought I might as well try to give the waterproof box insulating properties too.

One more reason for going the route of a waterproof box is that I dont want to drain the ground in this area of the garden too much

[david s]

I really think you are asking for trouble. See previous comment.

https://community.fornobravo.com/for...087#post403087

i use an additive (Xypex) to make my supporting slab waterproof, but have found using the recommended additions that it is only partially effective. Remember that even if you made it totally waterproof to prevent moisture getting in, it will also act to prevent moisture getting out.
Dry insulation like cal sit board is preferable to vermicrete because it is already dry but costs considerably more. Look at my experiment on attachment re drying vermicrete

If you could maintain an airspace of around 100 mm surrounding the sides of the insulation it would be better, but it will fill up with all sorts of rubbish from your garden and you'll be back to square one. Moist insulation is not very effective as it will conduct heat.

Vermicrete insulating slab copy.doc.zip

[UtahBeehiver]

What are your thoughts of placing perlcrete below grade?

[HenrikK]

An update. I'm trying to make a waterproof box to build the oven in. First step, gravel in the bottom and on top perlcrete with SIKA waterprofing agent . Talked to someone at SIKA who said it ought to work, but let's see. Plan to let it sit until the weekend to harden before trying to make the sides of the box. Do you think this would work?

[HenrikK]

The ground level must have been lower at some point. 12-15 cm below current ground level there is on each side what remains of a 10 cm thick concrete slab. This opens interesting possibilities for the construction as I would have absolute stability in the both sides of the oven that are 90 degrees to the opening.