28" homebrew cast oven in walled enclosure Belgium

[Kris S]

I plan on firing the oven (slowly and with caution) next weekend and make some pizza.

I stumbled upon this: https://community.fornobravo.com/for...ing-into-pizza

Could water glass - Sodium sillicate be used to treat the 'holes' inside my dome where small chunks have fallen out. because I fear they're a weak spot from which more and more cracks will form and pieces fall out off?

[Petter]

You can't patch the cracks, but you can impregnate the dome. It will form a silicate network once cured in the homebrew porosity. If it will prevent further spalling or not, I don't know. It worked well for the perlcrete. I don't think it would do any harm to the dome, so it only cost a few $ and time to evaluate.

[Kris S]

Hi Petter, I’ll give it a try then if it can’t harm.

I want to make my own Sodium Sillicate and found some recipes online. I think I have some silica gel at home and it’s easy to get some Sodium Hydroxide.

I have a few questions though, could you shed your light pls?

• What specific recipe did you use (water / silica gel / sodium hydroxide) (final % concentration?)
  in the abovementioned thread you mention:

"My Sodium Silicate was about 40 % solid...."

What exactly do you mean with the 40% solid? do you mean 60% water and 40% sillica gel + Sodium hydroxide?

• If I don’t have enough silica gel, I read you can use cat litter? I mean, do I interpret correctly that you can substitute silica gel with cat litter? And at a 1:1 ratio?

Thanks in advance!

[Petter]

I understand your questions but I'll not answer them. If you need to ask, you don't have the knowledge to deal with these type of chemical. I don't wish to be unpolite, I only care about your health. Manufacturing this is really nasty work, no matter what any you tuber say or show. Being outside with tail wind, mask, glasses and so on is not enough. I did my own but will never do it again. Buy a liter, it is more than enough and should cost less than $10. Store bought SS is in the 35-45 % solid range.

[Kris S]

Fair enough, I'll see if I can find it anywhere.

Sodium silicate goes under a lot of names, and I see both potassium silicate and sodium silicate products are being used for waterproofing (not my purpose), so can either of these be used for what I want to do, or should I specifically search for a sodium silicate product (with the correct CAS nr. 1344-09-8).



on a side note: the oven seems to have survived saturday's pizza firing without further cracks, but I'll wait and see this week when it's fully cooled down...

[Sidetrack]

Hi Chris,

Any large refractory section is vulnerable to cracking, primarily because of the difference in thermal expansion. A one piece dome in particular, using wood as a fuel is particularly susceptible. For this reason most cast oven manufacturers offer their ovens in multi piece sections. This makes things more manageable and less weighty sections. For mobile ovens some manufacturers offer a single cast dome as they're less likely to have problems with road vibrations. When I first began to build ovens I used a single piece cast dome, but now produce a 3 piece dome. Unfortunately this requires much more work to create a mould, particularly if the sections are to be step joined. This is hardly worth the effort for a single cast oven, the simplicity of the single cast, in situ, over a sand mould has way more advantages. The single cast does however have a tendency to produce a crack, just like yours has, which runs vertically right opposite the oven mouth.

Would it be possible or practical to set some paper or foil into a cast-over-sand dome to mimic a multi-section dome and control where the inevitable cracks form?

[Petter]

Fair enough, I'll see if I can find it anywhere.

Sodium silicate goes under a lot of names, and I see both potassium silicate and sodium silicate products are being used for waterproofing (not my purpose), so can either of these be used for what I want to do, or should I specifically search for a sodium silicate product (with the correct CAS nr. 1344-09-8).



on a side note: the oven seems to have survived saturday's pizza firing without further cracks, but I'll wait and see this week when it's fully cooled down...

You can use either, they form Silicate networks when cured.

Great that no more cracks formed. I have some 10-15 fires at 1100-1300 F dome temperature with no issues no. The cracks appeared at fire 2-3 during cooling.

[AndreasP]

Kris S , What opening did you go with? I am planning my oven and hope to cut the brick this weekend, then cast the dome. I am planning on a 32" internal diameter and am going back and forth between a 17" and 19" opening.
Larger opening = easier access
Smaller opening = more thermal mass, should retain heat better for cooking
Have you used the oven with your door size for pizza yet?

[Kris S]

Hi Andreas, I went for 19” width and 8.7” height.
If you can, I would advise choosing opening width over pondering about eventual heat loss.
With my rather small 28” diameter oven a 19” opening is pretty large and I probably lose quite some heat, but I’m happy I didn’t go smaller than that, it would not be practical.
19” is adequate but not luxurious, any smaller and it would annoy me I think.
I have done pizzas, a roast chicken, pasta sauce, some vegetable casseroles, 2 breads, some bbq ribs…

Something minor I would do different is have the oven floor higher, now the height of the floor is about 130cm I think (should remeasure to be sure), I would add 20cm to this, because I have to bend a little too much for loading and unloading. (I’m 1m87cm tall). But aesthetically I went for a little lower, should not have done that.

[david s]

I agree about the more generous oven mouth. Mine is 16” wide, but for a 21” diameter oven that’s pretty wide for a small oven, but as it’s fuel consumption is so low it’s no trouble to flash it up. Plenty of retained heat for roasts and bread etc.
I think for working height you just get used to whatever you have.

[AndreasP]

Kris, David, thanks for your feedback. I think I will stay with my original plan of a 19" opening for a 32" diameter oven. I could always stand up some firebrick along the side of the opening if I want a smaller opening.

As far as the floor height, I have a bit of a challenge. There is a big height difference between me and my wife. I am sure I will be the one cooking in the oven, so I have chosen my elbow height for the cooking floor.

[hughesyourdaddy]

Hi Kris,

Great build! I'm preparing to build an oven and will use yours as inspiration because I want to build 28" too. Can you remember how much clay you used in the homebrew mix in the build? I can only source by the kilo where I am so it would be great if you could let me know. Thanks.

[UtahBeehiver]

Look at Nick JC build, he did a really nice cast build and detailed out his materials.

[AndreasP]

I just finished casting my 32" dome and gallery. For done and gallery I used:

• 200 lbs of sand for the dome
  • I used some of the sand I used for the dome mould to cast the gallery a few days later, probably 30 lbs or so
• A bit less than 50 lbs of clay - I used up the complete 50 lb bag but used a few handful in the sand to build the mould for the dome
• Not sure on the portland cement and lime, but less than a bag each
  • maybe 2/3 of a 94 lbs bag
  • maybe 1/2 of a 50 lbs bag

Maybe this helps.

[Kris S]

25kg vermiculite + 25 kg perlite		35	+/- 2/3 used
25kg bags portland cement	2	7.5
25 kg bags sand for dome mould and homebrew	3	5
25 kg bag fireclay	1	17
+/- 10kg hydrated lime		0	free

Looking back at the used materials overview from my post #102 I bought 25 kg fireclay, I don’t remember exactly how much I used but I still have some left, maybe a quarter to a third.

I can weigh what’s left over so we know for sure, I’ll try to do that.