32 inch (ish) cast oven in Dublin

[skelly27]

Hi all

Thank you for this forum, I have learned so much and don't think it would be possible for me to build without the information here.

I have been building since June and just getting to the actual oven now so thought it was time I started a thread.

I am a complete novice and never laid a brick before this, but hopefully some other novices can learn something from my mistakes and indecisiveness (hence the long time building).

The plan is for a Pizza Oven, Santa Maria grill and work surface. Have planned for Homebrew cast oven. The garden is small and space is limited so wont fit much more than 800mm diameter. Planned dimensions are below, in inches cos almost all have come from this forum.

Internal diameter: 31.5"
Oven Walls: 2"
Insulating Blanket: 2"
Vermiculite Insulation: 2"
Render: 1"
External Diameter: 45.5"
Door width: 15"
Door Height: 10"
Chimney Diameter: 6" Single wall
Chimney Height: 39.5"

Floor will be made of fire bricks and 1" vermiculite board. I will build a sandcastle to cast and am currently torn between casting the flue gallery and using fire bricks for the arches (I can get pretty ones for €1 each. I was set on using bricks until I read david s said they can act as a heat sink. So back to the head-scratching.


Every step so far has been head-scratching but its movin along slowly.

Shane

[skelly27]

More progress photos

[skelly27]

[skelly27]

I have a couple questions. ANy help would be much appreciated.

1. david s mentioned that bricks in the flue gallery can act as a heat sink. is a cast flue gallery the best way to go for a cast oven?
2. is the door width of 15" ok? I read several times that door width should not exceed half the internal diameter, but the Forno Bravo Casa oven has a door width of 17" so im confused on optimal door width for a small oven.

[SableSprings]

Welcome Shane! Bricks in the flue gallery can act as a slight heat sink from the oven. Generally we plan for an insulating gap between the dome & gallery, but it is a minimal issue and a good insulated door is more important if you are going to do baking in addition to pizza. If you use a fiberglass rope (used around oven doors) in that space between your cooking floor and the entry bricks as a heat break and expansion gap, you'll prevent quite a bit of heat loss/transfer from the oven chamber/floor out. I am more concerned with your initial design listing where you note only a 1" vermiculite board for the insulation between the hearth slab and your cooking floor bricks. We usually recommend 4" of a 5:1 mix of vermiculite (or perlite) and cement for the base insulation or 2" of CaSi board. Any less and you will find that you'll lose significant heat to the concrete slab which will be a much bigger problem than the heat loss to the flue gallery or landing. I agree with david s that for most ovens, the cast gallery makes the most sense in terms of weight and the ability to form a smooth collection path/flow to the chimney.

In general the width is normally not an issue except you want to make sure it's wide enough to accommodate your peel, sheet pans, or other cooking utensils you intend to use. Often it is simply the brick lengths that ultimately determine the opening . Don't forget to plan a reveal (the little edge that you use to press the door against when closing the oven opening). Hope that helps.

[skelly27]

That helps a lot, thanks SableSprings . Found some Silca board in Dublin but not CaSi. Is that the same? https://www.silca-online.de/fileadmi...A-250KM_EN.pdf
I'll make sure there's a small reveal for the door.

[Gulf]

skelly27 I edited your link so that it would go directly to the Product Data Sheet.

[UtahBeehiver]

The silca board is adequate (K value = 0.1), not quite as good an insulating value as CaSi (K value = 0.05) but better than insulating fire brick (K value = 0.15). Should be min 2" thick, compressive strength is very good 145 psi, min recommended 70 psi.

[skelly27]

Great, thanks Gulf , UtahBeehiver
I bought the silca board and will build the sandcastle tomorrow.

Included some of the tools made to hopefully make it easier. Will cast the dome and gallery separately so only made the form for the door. Learned a lot from Mullster thread so have put duct tape around any exposed mdf and will oil also to prevent sticking. All screws are accessible from the outside in case I need to take it apart to remove.

Tiece of wood with the screw has been very useful in drawing the many circles and arcs I've needed. Tried to make the curved trowel too but a combination of crappy old plywood and bad technique doesn't make a pretty tool.

[sergetania]

My oven is 30" diameter with 19" wide opening. It helps accessing the cooking chamber especially when using 12" cast iron pans. Definitely a plus, not a problem.

[skelly27]

Thanks for the tip sergetania . I may have come too far to go back now though.

Have build the sand castle with door frame in place. I looked at the forno bravo specs or their casa modular oven and it's 17". 16" fits my landing layout but hopefully wont be something I come to regret.

The sand castle used way more sand than I was expecting, almost 175kg and I used as many bricks as I had lying around to fill the centre. Sand may have been too dry when we first started applying, added more water towards the end.

Had to re-cut some of the floor bricks as well. The arc I cut as a guide for the sandcastle was very helpful.

After it was built I put on a layer of newspaper and later on came back to paper mache some extra paper on to hopefully create a smooth finish on the internal dome.

Very satisfying part of the build.

Like every other part of this build though, it took longer and was full of doubt and design changes in the middle.

Next oven will definitely be planned better but I think if I had tried to get every element nailed down before starting, I never would have started.

Will add some pics later.

Shane

[Boogie-D]

Keep it going Shane I’ll be following you as I go along with mine... aloha!!

[skelly27]

Cheers Boogie-D . Hope alls going well on your build. Did you get all the materials?

I built the sandcastle last weekend but didnt get to cast until this weekend.

Casting was going well, the only slow part was mixing the homebrew, which was by hand. I read on the forums somewhere that it was a bad idea to put lime in a mixer for toxic reasons so went manual.

All was going well until we finished the dome and it starting slumping fast. It got so bad that the whole back side nearly slipped off, a big crack formed. I was fairly desperate at that point and could just see the whole thing slipping out of my hands.

We spent another 2 hours in a battle against the slump before eventually tying some thin foam padding around the base which seemed to stop it.

Later that night I came back to it to fix the slumping and seem to have been able to fix it. It's curing now in decent shape although I dont know if that back part slipping down may have caused irreparable damage.

I think the reason for the slumping was that the homebrew was too wet at the start and created an unstable base. I didnt have a form around the bottom either and may have been moving too fast in eagerness.

I have 2 questions, if any of you could help?

1. Should I add extra homebrew to the areas that thinned out from slumping? My logic is that it would even out the mass of the oven and prevent cold spots from uneven dome wall thickness.

2. Is there anything I should do to help strengthen the back wall that cracked (maybe tore is more appropriate) during slumping? I keep picturing the whole back wall falling off when I light the curing fires, as I collapse into a tantrum that would put our 3yo to shame. Followed by all the other stages of grief.

[Boogie-D]

Hows it going Shane..?? Still waiting in Hawaii but at least the surf has been firing

[Boogie-D]

Any updates Shane?