New member and first Portable 32" build

[david s]

Hi Nate, by my calculations you'll need more.
32" (813 mm) for simplicity let's just call it 80 cm diam. So R1= 40
V1 (r40)= 4/3 x Pi x r3
V1 = 268000 cc or 268 litres
V2 (r45) = 381
V2-V1 = 113
but half because it's a hemisphere, so your dome volume is 56.5 litres
as you get around 15 litres of wet castable per bag, you'll need 3.77 bags. As you'll also need more to cast the flue gallery you can probably say another bag, depending how thick you make the casting. So that brings it to 5 bags. I think you'll need to go back and get another three bags.

check my calculations "measure twice cut once"

Here's a good thread to follow https://community.fornobravo.com/for...and#post396954

For a one off cast the extra trouble and work required to do a multi piece casting is not worth it IMO a one piece casting works fine. The main advantage of a multi piece casting is that the pieces are more easily moved, but if you cast in situ then you don't have to move it.

[NateQLDer]

Hi Nate, by my calculations you'll need more.
32" (813 mm) for simplicity let's just call it 80 cm diam. So R1= 40
V1 (r40)= 4/3 x Pi x r3
V1 = 268000 cc or 268 litres
V2 (r45) = 381
V2-V1 = 113
but half because it's a hemisphere, so your dome volume is 56.5 litres
as you get around 15 litres of wet castable per bag, you'll need 3.77 bags. As you'll also need more to cast the flue gallery you can probably say another bag, depending how thick you make the casting. So that brings it to 5 bags. I think you'll need to go back and get another three bags.

check my calculations "measure twice cut once"

Here's a good thread to follow https://community.fornobravo.com/for...and#post396954

For a one off cast the extra trouble and work required to do a multi piece casting is not worth it IMO a one piece casting works fine. The main advantage of a multi piece casting is that the pieces are more easily moved, but if you cast in situ then you don't have to move it.

Again thank you David, I have 3 bags to start and looks like ill have to go back to get more to do the gallery, at least its close! I was thinking of casting in place but i was thinking if i section it, then there are pre existing weak points for thermal expansion and contraction during firings. I didn't want it to crack all crazy on the inside. Or is that unlikely as its isn't that big a structure?

Kind Regards,

Nate

[david s]

If you cast it in one piece you will get some hairline cracks. My oven here at home is a one piece dome, is about 9 years old and the hairline cracks haven't got any bigger. I should think the oven will outlast my grandchildrens lifetimes. My mobile oven which I built around the same time (see in mobile deconstruction under other oven types) did have a larger crack at the back, but it got an absolute flogging from customers over firing and very frequent use. As it is my demonstration oven it needs to maintain a "newish" look. I still don't think it's worth casting in sections for a one off. I do now cast my ovens in three sections, but it took a lot of work adapting the mould. The big advantage is that a three piece dome is way easier to move than a single section.

[NateQLDer]

If you cast it in one piece you will get some hairline cracks. My oven here at home is a one piece dome, is about 9 years old and the hairline cracks haven't got any bigger. I should think the oven will outlast my grandchildrens lifetimes. My mobile oven which I built around the same time (see in mobile deconstruction under other oven types) did have a larger crack at the back, but it got an absolute flogging from customers over firing and very frequent use. As it is my demonstration oven it needs to maintain a "newish" look. I still don't think it's worth casting in sections for a one off. I do now cast my ovens in three sections, but it took a lot of work adapting the mould. The big advantage is that a three piece dome is way easier to move than a single section.

Hey David, by the time i had read this i had already geared up for sectioning it into three pieces plus gallery. I kinda thought you would say sectioning is best. Last night i "poured" my first section and it took probably 1.5 bags, so i think your right on the 5/6 bag estimate. First pass i had a little bit of slump which i rectified quick smart (just fraction to wet) second pass was perfect. The thickness is basically uniform. 2.5-3 inches at the top and bottom and one side a little light on 1.75 inches so it will get a top up as i put it all together.

I will cast the second section tonight after i sleep (night shift last night)

Side note, there are no burn out fibres in this mix but the company says it the one they use for making their pizza ovens so should be ok i think??

cheers Nate

[NateQLDer]

[NateQLDer]

[NateQLDer]

Thought i might post an update. DavidS you were right, five bags it is had to go back and pick up another two. So the casting of the main dome is all done, except the keystone piece at the top and has set hard a a rock! I cast into three pieces. The pieces fit perfectly together which is nice, I made two errors though, neither fatal just annoying. First the base of the dome on the front section is a fraction wider than i wanted and doesn't sit on the firebricks on either side. I have include pics for you to see. i was thinking of when i bed the dome in with a wet slurry of the concrete i might make a smooth buttress on the inside to cover the vermicrete thats exposed? what do you think? would that work or would it crack off?

Second mistake was i think the front section hasn't allowed enough room for a gallery of sufficient size to accomodate a 6" flue. I either have to cut into the dome or extend the gallery... unless a 5" flue will suit this size oven? Any advice would be appreciated

Pretty stoked overall how its come up. It looks the part so far at least anyways

Cheers Nate

[david s]

If you want to add any more castable to existing cast, do it asap while there is still moisture in the casting. Also to assist bonding, sieve out the coarse aggregate from some castable and make a thin slurry with it to coat the area you want to add more castable onto, just prior to adding the fresh castable. This will help the bond.

Regarding the gallery issue you can push the gallery further over the oven entry which allows you to accomodate the flue but keeps the entry shallow. The pic on this post should explain what I mean, if the attached pics don't.

2
You need a 6" flue for your sized oven, but another solution would be to bend the bottom of the pipe into an oval so it has less depth.

[NateQLDer]

If you want to add any more castable to existing cast, do it asap while there is still moisture in the casting. Also to assist bonding, sieve out the coarse aggregate from some castable and make a thin slurry with it to coat the area you want to add more castable onto, just prior to adding the fresh castable. This will help the bond.

Regarding the gallery issue you can push the gallery further over the oven entry which allows you to accomodate the flue but keeps the entry shallow. The pic on this post should explain what I mean, if the attached pics don't.

2
You need a 6" flue for your sized oven, but another solution would be to bend the bottom of the pipe into an oval so it has less depth.

Awesome idea with the flue! I think the link to your deconstructed one really helped! I will start to design the mould tomorrow As for the adding of cement... Well i tried the next day and it was like a rock, all mix even thin slurry just seemed to fall off. I even tried roughening up the surface with a grinder but no avail. Its only one of the sections and only one small bit that just under the 2inches think so will have to do i hope. I learnt my lesson for the remaining castings though and the thickness is good, too thick perhaps. The front casting is easily 3" in spots haha. What would you suggest for the exposed vermicrete though? should i just cover with a coat of cement and bed the dome in? could i make a buttress around the inside? I don't know considering the fact that the cement won't stick to hardened cement ....

Sorry one more question, Should i use high temp motor to join the sections of the dome?or just push them together? they fit snugly

Cheers for all the advice i really appreciate it

[david s]

Vermicrete won't stand up to the intense heat in that position. Covering it with a thin layer of castable probably won't suffice either. If it were mine I'd dig out least an inch of the vermicrete and replace it with castable. As you don't want any bits falling on your food I'd suggest you only fill the joins between the castings from the outside. Again, presuming you have some castable left, the sieved mix makes a very good high temp mortar.

[NateQLDer]

Thanks again David , good idea about digging out the vermicrete, will be a suitable pain in the ass to cut out but necessary . I have a bag of high temp motor and will use that from the outside when i have finished adding the necessary refractory. Still have 3/4 of bag refractory cement so i should have enough for the flue plus the bits to fix the exposed vermicrete. Will post pics when i finish those bits

[NateQLDer]

So I haven't updated this for a while. This morning i finally finished the last of the mosaic around the pizza oven. I have fired it several times and it perfects amazingly! Here are some pics that follow through the progress. That said there aunt as many of each stage as i would have liked but its hard to take pics with dirty hands so it is what it is

I cast the gallery in three pieces with embedded chicken wire for extra strength. I did this for ease of formwork. The overall effect works well and is super strong or at least appears to be so far.

[NateQLDer]

So in these pic i have finished the gallery - the yellow stuff is left over builders foam, i used it to hold up the formwork inside the gallery.

After the ceramic matting was put down, i covered with chicken wire and tied down tight - not easy or fun job haha

Also, i covered the dome with 2" of the ceramic matting but over the gallery i though 1" would be sufficient - this is incorrect lol the gallery is the only place on the completed oven now that gets hot on the outside - like 70 degrees C. Also if you look closely i didn't put a strip of the ceramic blanket in front of the flue. This was also a mistake - i get two cracks that form when I'm firing the oven... can you guess where they come through? right over this spot that had no layer of ceramic blanket. After firing the crack disappears and I'm hoping with continued firings it might eventually dissapear but not much i can do now.

[NateQLDer]

[NateQLDer]

So here the stucco has all been completed. Now i didn't take any pics of this next bit but the stucco was then coated in four layers of waterproofing concrete made into a paint and painted on. The same stuff used to waterproof concrete fish ponds. After several days of curing, a flexible waterproofing membrane was painted on - thats the bright green stuff.

The next stage is sticking on the the 2.5 cubic meters of smashed tiles it took to cover the dome and base.