Cast dome with 2nd hand arch. Queensland.

[Nicholasd]

Hi Everyone,
So after lurking here for a while I am getting closer to actually starting. So much information to absorb.
I would like a pizza oven and decided to DIY it to save money and try a big project.

I managed to get myself a . Some guy who demolished the rest of it saved this part of it and five flue segments and some oven tools. I thought this is a good starting point and cost AUD$250 for all of it. He had none of the firebricks...

If you look at my pics and the link, the door is kind of a weird shape (and very rusty!) This is the extra wide model.

I just want a normal sized oven with the possibility to cook on retained heat.

I am on the Gold Coast,Qld. For local supply hints it would be appreciated.

Here is my plan so far.

Starting from the base.

Hebel stand either on blocks or vertical Hebel board. The oven will go in a corner and may also rest on a retaining wall.

100mm Vermiculite insulation.

Fire bricks to cook on (not sure on available thickness in Australia seen various interstate )

50-70mm Cast homebrew dome to save money.

200mm/8" flue with hat. More would be good as neighbours are close and it is at the bottom of a slope.

Door height 280mm/11"

Dome height 440mm

Dome internal base 880mm/34 inch (Not sure on this, seems small)

50mm Ceramic Blanket

100mm Vermikulite mix insulation over dome to base insulation. (not Hebel board)

Render/mosaic.

No roof.

How am I doing so far?

I am worried about joining the arch to the rest of the dome. I think some reinforcing wires had to be cut to demolish the oven. Some are present on the door frame. I presume that the arch is in position when forming the dome mold.

Any input would be greatly appreciated!

I have more photos I'll upload soon.


Nicholas

[UtahBeehiver]

Approved, commercial link removed

[Pizzarotic]

I am on the Gold Coast,Qld. For local supply hints it would be appreciated.

I'm not aware of any suppliers on the GC for the bricks.
Mr Stoves in Brisy for the flue.
Nerang Hydroponics for the vermiculite & perlite.
jimbennett949@gmail.com is in Caboolture and can supply the bricks and insulation etc.

Fire bricks to cook on (not sure on available thickness in Australia seen various interstate )

Standard 3" brick for the floor. You can use the larger 12" square brick tiles to minimise the number of floor joints. They only come in 2" which is adequate but the 3" would be better for retained heat.

How am I doing so far?

Looking good.

I am worried about joining the arch to the rest of the dome. I think some reinforcing wires had to be cut to demolish the oven. Some are present on the door frame. I presume that the arch is in position when forming the dome mold.

It's not a big deal as it's not a structural join. You will probably need to do some shaping of the arch tunnel to match your dome shape. Fit the tunnel through to the inside of the dome and plaster over it when you cast the dome, that will keep it secure.

[Nicholasd]

Thanks for the reply and information.
Had a look at the hydroponic shop and they have different grades of vermiculite. Which is recommended?

Which is better for insulating the slab and done, perlite or vermiculite?
I may also need to change how thick the vermiculite is on the Hebel board as the retaining walls are about 50 mm higher than I thought. Can the vermiculite be 40-50mm thick on the slab? Or should I use cal-sil board@ 25mm?

Thanks.

[david s]

The answer to some of your questions is on this thread, with detailed explanation.
https://community.fornobravo.com/for...ion#post448045

perlite and vermiculite are interchangeable and once mixed with cement produce the same strength and insulation value for a given equal cement addition.
The finer the grade the more water is required in the mix to get workability. This does create a problem because the extra water, above that which is consumed by the hydration process needs to be eliminated for the insulation layer to hold heat and any steam escaping too rapidly swells and cracks the layer.
I’ve also found a mix of grain size makes a more workable mix. This is useful for lean mixes (10:1) or leaner but unnecessary for richer mixes (5:1) or richer.
I currently use a fine vermiculite and a medium perlite mixed 50/50 with a(10:1) mix and it requires, by volume 4parts water.

[Nicholasd]

Coming back to the oven project...
How does this idea for the base look like. The minister for planning, development and aesthetics would prefer the oven in the corner. Part of the oven will rest on the retaining wall.
Please have a look at the mock up. The blocks are 190mm square, please ignore the full blocks at the bottom as I didn't have enough half blocks. They will be mortared in place. I will probably core fill them.
On top of this will go the Hebel, cal sil, fire brick.

[david s]

I don't know how heavy your oven will be, but most are way heavier than you'd think and therefore sit on a 100mmm reinforced concrete slab. By cantilevering the slab over the piers (as shown) you can reduce the span between the piers and go a bit thinner. But remember that the strength of a concrete slab is proportional to the square of its thickness. This means a 50mm slab is only 1/4 the strength of a 100mm slab. Hebel, from my experience is not particularly strong. I used Hebel Power Panel (steel reinforced 75mm thick slabs for my mobile oven. After 8 years of use on dismantling it the Hebel looked like this. Maybe partly due to road vibration and bumps, but I didn't use it again on the rebuild.
Judging from your pic the blocks are sitting on pavers. They may not have sufficient foundations under them, likewise the retaining wall.If you don't have block laying skills I highly recommend using masonry adhesive (eg Selleys Landscape) drill a hole in your concrete into which you can hammer a steel bar that will sit in the middle of the block cores up to the top block., mortar the first block, glue subsequent blocks on then fill the voids with concrete.

[Nicholasd]

Thanks for that info.
The oven sits on a concrete slab with a painted pattern on it.
The retaining wall sits on foundations but I'm not sure of the quality of this work as some of the walls are not filled with gravel.
"drill a hole in your concrete into which you can hammer a steel bar that will sit in the middle of the block cores up to the top block., mortar the first block, glue subsequent blocks on then fill the voids with concrete."
I was wondering about reinforcing the blocks to the slab, this looks like a good solution. Would this wick moisture up through the blocks? I was going to lay plastic under the blocks to help prevent this or is this not an issue with a core filled block column this high?
Our outdoor area is long, narrow and terraced so we don't want to take up too much room with an oven hence putting it in the corner hanging over the retaining wall. We do have some area up some stairs to a terrace above this but the ground is absolutely full of roots of now dead palm trees and isn't stable. I might think about that one though.
I'm also thinking about pouring my own slab instead of Hebel...

[david s]

I think you’d be better to get a decent bond between the bottom blocks and the concrete under them, so plastic there maybe not the best solution. I use an additive in my supporting slab that makes it waterproof, or at least reduces porosity, to prevent wicking. Another method is to use a sealer on top of the filled blocks prior to Hebel or concrete slab on top. Some sealer between the under floor insulation and supporting slab is also prudent.

[Nicholasd]

Here is an update to my oven.
Eventually went with a slab as it was difficult and expensive to get hebel board.

Slab is 75mm thick and has 5mm mesh in with thicker bars crossing the whole slab.

Next is to make a little platform to sit the arch on so it is the correct height to the finished floor of the oven. I was going to use permacrete for this in a 5:1 mix for strength. How does this sound?

I also have some questions about the CS board and how big to cut it for cast dome on brick (85cm/33"). I just have to measure and make a template to help with that.

[Nicholasd]

Just found this about making strong perlcrete.

From David s "You can make up a standard 3,2,1 aggregate, sand, cement concrete mix and use the perlite as the aggregate. This produces a fairly strong result, but reduces the insulating capacity. If you want it even stronger then make the aggregate portion of the mix 50% perlite 50% standard aggregate. Be aware that perlite takes up a large amount of water that you need to eliminate later."

The reason I am wanting strong concrete is to build a 100mm platform for the arch/gallery/flue to sit on. (photo at the beginning of the post).

[david s]

If you are looking for strength in your supporting slab, don’t replace any of the heavy aggregate with either perlite or vermiculite. As your slab is only 75 mm thick you’ll need it as strong as you can make it. The strength of a slab is proportional to the square of its thickness. So a 75mm thick slab is only 1/2 as strong as a 100mm one. Replacing aggregate with perlite or vermiculite will further weaken it.
However, if you mean a cast slab on top of the 75mm one, yes you could make it weaker and lighter. A 5:1 vermicrete is considered strong enough (but don’t go weaker), as an insulating slab, on top of which an oven can sit.

Did you cast in some weep holes in the supporting slab to assist water removal from under the floor? If not they can be drilled after the slab has been cast.

Regarding the cal sil board, a minimum thickness of 50 mm is usually recommended. It depends on what thickness you can get. I have some that is 50mm, but more recently have only found 40mm available, so I do 2 layers. To obtain the equivalent insulating value of a 50mm cal sil board using a 5:1 vermicrete, you need to cast it 100mm thick.

[Nicholasd]

Main slab is poured with normal aggregate mix, mixed strong with more cement.

The perlite platform is just for the arch to get to the height of the CS (60mm) and firebrick (75mm) so its the same as the floor of the oven. I will have a 8mm(?) thermal break before the CS. I ended up using the very strong mix 3:2:1 so it is really strong but not very high insulation properties.

I planned weep holes but forgot! Should I drill them while the concrete is still a bit green? How many weep holes for a 85cm oven? Also do they need to line up with holes in the cal sil board (one piece) ?

Next step. Cutting the CS board to shape of the dome. 50mm casting on the firebricks.

• Am I correct in thinking that the CS board should be the same diameter as the external size of the dome? ie an 850mm/33" +50mm cast, will have the CS board cut to about 90cm. The Ceramic blanket goes all the way to the slab.

Thanks and have a good new year!

Nicholas

[david s]

How far out the CS board should be makes little difference as long as the whole oven is insulated under and over. Both CS board and blanket are super water absorbent so the parts in contact with the supporting slab also makes little difference. The 3 pics explain it better.(my own preference is 3). The oven can sit on top of the floor bricks or on the CS board.Sitting on top of the bricks is my preference because it does not require precise brick cutting at the perimeter. The downside is that you will never be able to replace a floor brick that is sitting under the dome. Any that ever get such a beating will be in the centre though, so that's not an issue.

If drilling the weep holes do about 3 near the centre and use a small pilot drill first in case you strike the reo. Enlarge the holes with around a 1/2" bit. glue some insect screen over the top of the holes to prevent creepy crawlies.
Also a good idea to place some ceramic tiles on the slab before placing down the This will allow water vapour a pathway between the tiles and out through the weep holes as well as elevating the CS board from getting wet if water enters.

[Nicholasd]

I managed to drill some weep holes in the slab.
I found some tiles in the garage that I can use under the CS board. They are fairly large 300mmx300mm so I was going to break them up in to pieces like in the pic. How does the size of the pieces and spacing look? I may have to get more as I may not have enough, but at this spacing of the pieces I may be able to get away with it.

I have seen pics where people put the glazed side down? Not sure on this though.

Cutting the CS today as in pic 3.