Vermiculite, Gym Ball Dome, Wood Fired Pizza Oven

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I built this pizza oven for my family instead of buying a similar one for at least £700 ($900). The ones you can buy still require a base to be made or bought and you have to assemble the oven as well. I was able to create something unique and bespoke to fit the small space that I had available.

I hope that you decide to make one for yourself. You will enjoy cooking (and eating) tasty stone baked pizzas that cook in seconds as much as you will enjoy the satisfaction of having made the oven yourself from scratch.

I spent under £320 in total on materials. The only parts I already had available for free were the 14 house bricks and scrap wood to make the jigs and some hardcore for the base.

I hope you enjoy making your own wood fired pizza oven! Go create!

Supplies:

x8 Paving slabs 450x450mm (builders yard) -£18.40
x32 Breeze blocks - 100mm (builders yard) -£43
x4 25kg Bags of sharp sand (builders yard) -£8.50
x4 25kg Soft building sand (builders yard) -£8.50
x4 25kg Plastering sand (builders yard) -£11.20
x2 25kg Bags of Portland cement (builders yard) -£11.00
Quantity of hardcore material such as broken bricks and/or rubble
200 Litres of 2-6mm grade vermiculite (Amazon) -£58
x1 Calcium silicate insulation board 500x1000x50mm (eBay) -£35
x26 Fire bricks 25mm thick (eBay) -£40
1m x 1m of chicken wire (garden centre) -£5
1m x 610mm x 25mm Ceramic insulation blanket (Amazon) -£23
1x 1kg Tub fire cement (eBay) -£5
x14 House bricks (builders yard) -£10 - 15
5L of exterior paint (builders yard) -£10
75cm Gym ball (eBay) £7
500mm of 8mm Fire proof rope (eBay) -£5
x2 150x500mm Stackable stainless steel flue pipes (eBay) £21 each
Wood for dome jig (Home)
Wood for arch jig (Home)

+/- £320 total


Suggested Tools include:

Angle grinder with stone cutting blade
Electric jigsaw or handsaw
Hammer and bolster chisel
Electric drill and drill bits
Wheelbarrow (or similar to mix cement)
Bricklaying trowel
Plasterers trowel
A few buckets
Spirit level
Spade for digging
Hand compactor
Dust masks
Scissors
Staple gun

Teacher Notes

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Step 1: The Base / Foundation

For an oven this size, clear an area larger than your intended base. For my base of 0.9m, I cleared an area of 1.2m square.

I used concrete paving slabs for the base instead of pouring a slab of concrete. They are very thick, strong, solid slabs - perfect for the base.

First, compact the ground beneath where you want to build your oven then add approximately a 15cm layer of hardcore material to build up a solid sub surface. The gaps between the hardcore should then be filled in with a few bags of 'scalpings'. Then go ahead and compact everything down as solidly as possible with a hand compactor or something similar and heavy.

Using string and pegs, mark out a square area equal to the final size of your four slabs and then fully bed the slabs in with a 3:1 mortar mix - 3 parts sharp sand, 1 part Portland cement to a thickness of about 15cm. Don't be tempted to economise on materials by 'dot and dabbing' as you will create a weak base with air pockets. Use a spirit level often to make sure the base is nice and level as you go.

Step 2: The Vermiculite Gym Ball Dome

To make the dome you will need to construct a simple jig to support the gym ball. The jig is basically a crude table with a 700mm circle cut out of the middle. I made mine out of scrap wood that I had in the garage. Once you have made your jig similar to the one pictured, you can then inflate the gym ball in-situ inside the 700mm hole of the jig so that an upper hemisphere is jammed into the jig securely. Cover the top half of the gym ball and the lower edge with food wrap to stop the vermiculite cement mortar from sticking permanently.

To make the vermiculite cement mortar (or vermacrete), use a plastic plant pot or small bucket to measure out 6 parts vermiculite and 1 part cement. Begin to add water slowly. You don't want a watery slurry, but mouldable clumps - it's quite difficult to describe actually... Err on the slightly drier side.

Some people say that they add pins or poly strands to the cement mix but I added neither and my oven has had no cracks so far after one and a half years of usage, one cold winter and about 25-30 firings.

Start loading up the sides of the gym ball with the first layer of vermiculite cement mixture with your hands, clump by clump. With the first layer complete, add a further layer until the dome is about 20cm thick. There is no need to let the first layer dry before you begin the second layer.

Over the next week keep your dome slightly damp by spraying it lightly with water DAILY and covering it with plastic (I used bin bags). Don't soak it - the goal here is to slow down the curing process by not letting it dry completely.

After one week, uncover the dome and allow it to fully cure and dry out. Do this at room temperature. Don't be tempted to warm it up with a heater or put it in the sun. You want it to dry out slowly. This took my dome about one month to cure fully.

When I made my dome, I also made some test lumps of vermiculite cement mix so that I could see how the curing and drying process was going.

Step 3: Building Up the Base Walls

Lightweight breeze blocks (as they are called in the UK) were used for the base walls of structure because they are easy to shape, cut to size and handle. I used a slightly weaker mortar mix of 4:1 for the brick laying. Four parts soft building sand, one part Portland cement.

Continue to lay blocks until you reach your intended height. I have no bricklaying experience and it wasn't to difficult - just use a spirit level all the time to check that it is all straight.

You are welcome to copy my design & layout for the block laying and I have included a detailed & to scale technical drawing. (See attached: Pizza Oven.pdf.)

I sculpted curved arches out of this versatile material to make a nice final arch shape. Six more breeze blocks were placed on the top horizontally to form a roof to the base.

Finally, cap the structure off with a further four concrete pavers - checking for level again as you go!

I used a total of 32 breeze blocks for the walls and eight paving slabs for the top and bottom.

Step 4: Oven Floor Insulation Layer-up

The next layer is the calcium silicate insulation board. Release your dried vermiculite dome from the jig by deflating the gym ball and passing a knife around the bottom edge of the dome. You may need some help lifting the dome as it's a bit scary... dropping it now would waste a lot of time and effort!

Place the dome on top of the calcium silicate board and outline the shape onto the board with a pencil. Use a jigsaw to cut the ceramic insulation board shape but be careful, this material is quite brittle. You'll also need to wear a dust mask as the dust is apparently harmful and can irritate your lungs. Fix the board permanently on top of the four paving slabs with some fire cement applied with a tiling comb and then press it down firmly. Fill any breaks or cracks with fire cement. My board did crack as you can see in the picture - it's no big deal.

Fire bricks: Test arrange your 25mm firebricks on top of the silicate board. Once again, place the dome on top and trace the edge to make your cut line. Number the bricks if you are worried about mixing up the bricks during cutting. I cut my bricks (badly) with a hammer and bolster chisel but it worked. A cleaner finish would be achieved with an angle grinder if you have one.

Next, bond the fire bricks down with another thin layer of fire cement. You can skip this step because the whole insulation slab will be encapsulated with a final layer of vermiculite concrete layer later on.

Step 5: The Brick Archway

Now it's time to cut your arch and bond the dome to the base.

First, build a semicircular jig from scrap plywood to support the brick arch as you build. You can get the size of the semicircle from the scale plan PDF attached to step 3. Trace the contour onto the dome and cut it out with a jigsaw or handsaw.

Bond the dome to the base with either left over fire cement or a quantity of vermiculite cement mortar using the same recipe as for the dome itself.

Allow to dry for a few days and then go ahead and light the first of many 'curing fires'. Make a fire out of a small quantity of sticks, nothing more. You are just trying to get the dome slightly warm.

You must protect your pizza oven from any rain between the curing fires- rain will soak in to the vermiculite and potentially cause damage at this stage in the build.

Trim your house bricks with a bolster and hammer or an angle grinder to match the contour of the dome as closely as possible. Bed the brick arch in using the arch jig for support and using a standard 4:1 mortar mix. Four parts building sand to one part Portland cement.

I added an extra brick on the top of the arch as a design feature / somewhere to put a glass of wine :)

Step 6: Insulation Blanket Layer

The whole point in a pizza oven is that they reach insane temperatures. To achieve these high temps, you need to add lots of insulation: Vermiculite dome / ceramic blanket / more vermiculite / exterior render.

Unroll the ceramic fibre blanket and cut 'darts' so that the blanket can follow the curves shape of the dome. Cut out an approximate chimney hole roughly where the the flue will go. The hole you will cut through the dome will be a 130mm hole which is smaller than your stainless pipe. This is so that the pipe will sit in its position without falling down through.

Pin the blanket down by stretching chickenwire over the whole dome. I used a staplegun with long 30mm staples.

Light another gentle curing fire whilst you're at it - not too hot please but bigger than the last fire!

Step 7: Final Layer of Vermiculite Insulation

Wrap your flue pipe with a layer of cardboard. This will act as a shim and protect the pipe as you add the next layer of vermiculite insulation.

Mix up batches of vermiculite cement and begin packing it over the blanket and chicken wire. It sticks quite well and is very satisfying. I did the whole lot in one thick layer.

Once dry (not cured yet) you can slip the cardboard covered flue template and you will find that you have created a nice socket for taking your flue down when the oven is not in use. When in use, seal the flue to the oven using a length of ceramic stove rope.

Light another curing fire... no high temps though yet.

Allow your dome to dry out - I felt like mine was sufficiently dried in five days as it was summer, but use your best judgement.

Light a curing fire as often as possible over the next two weeks, gradually increasing the temperature and size of the fire every time. Be patient - don't rush or skip this step or be tempted to light a big fire as the oven may crack if you go too hot too soon. Towards the end of this process you could go hot enough to cook a pizza.

Step 8: Render the Exterior Surfaces

The render coat of plaster is made with the following 6:1:1 recipe. That's six parts plastering sand, one part Portland cement and one part hydrated lime. The lime is important because it gives the plaster some elasticity.

Splat the render on with a plastering trowel if you have one. I'm no expert plasterer and we're not looking for a perfect finish here! Aim for about a 10mm coat. Go ahead and plaster the front and sides of the base whilst you are at it.

Allow to dry for a day or two and then paint with exterior masonry paint - I used Sandtex.

Step 9: Make a Door

Use the brick arch jig template you made earlier to get the rough size for the door. The door is an important part to be able to get your oven to its maximum temperature.

I made the mould out of yet more scrap wood and a bendy strip of fibreboard. I used copper pipe insulation cut in half to mould air inlet passages.

Pack the mould with more vermiculite mix (same recipe) and allow to cure for a week or so. I incorporated an unused kitchen door handle into my oven door which gets a bit warm but does the job.

Whilst my door was drying I couldn't resist and fired the oven up using the arch mould as a door. As you can see from the picture the door didn't last long - the pizza was still excellent!

Step 10: Aftercare & Tips

After use, once the oven has cooled down, remove the chimney and cover the oven with a garden patio table cover from the garden centre.

I will probably repaint the exterior every 2 years or when we fancy a chance of colour (it's yellow at the moment)

Start your fire at about the same time you make your dough (Jamie Oliver recipe by the way!)

Buy a £10 infrared thermometer from eBay!

Pizza cooks best with a flame (in other words, not just hot embers) the best way to achieve this is to have your fire going at the back and keep a few small logs on the opposite side "heating up'. When you are about to cook a pizza, throw the warmed log onto the embers and it will burst into flames!

Use coarse semolina to stop your base sticking to the pizza peel.

We tend to have parties where we ask guests to 'make their own' and then I cook it for them in the oven - it goes down very well.

I wish you the best of luck and enjoyment out of your new pizza oven. Go entertain your friends and family!

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    22 Discussions

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    lkjfdsa

    16 days ago

    Vermiculite contains asbestos mineral, you should buy a filtered mask for working with it.

    2 replies
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    leophamlkjfdsa

    Reply 15 days ago

    I personally extremely doubt it... This is likely related to a report about a mineral mine that was closed in the 1990's. Some houses built in the US during that era were insulated with this specific vermiculite from that specific mine. Since then the mining of vermiculite is thoroughly regulated. Vermiculite for gardening will be safe but if in doubt, wear a mask, vermiculite is quite dusty anyway so just wear a mask would be my advice.

    Remember that anything you read on the internet may or may not be correct - Including my own advise above. Just wear a mask if you’re worried about it.

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    pridesleapleopham

    Reply 12 days ago

    The Montana mine you mention produced 70% of the US supply and 80% of the worlds supply of Vermiculite at peak production and it is estimated that 35 million US homes contain asbestos contaminated vermiculite insulation. This is not a small problem being blown out of proportion by an internet rumor. There are justifiable reasons to be concerned where blown in insulation has been installed.

    The US EPA conducted testing of consumer gardening materials containing vermiculite in the early 2000’s, four years after the Montana mine was closed. It still found asbestos in vermiculite sourced from other mines although only a small percentage contained asbestos and and even smaller ( 2-3 products out of 35 tested) contained high enough levels to be a concern. The point here is that asbestos contamination is possible where ever vermiculite is mined because the two minerals are formed via similar geological processes. Not every load of ore is thoroughly tested and therefore not every product can be quaranteed to be free of asbestos. Just like how not every sheet of gypsum board can be guaranteed to not contain heavy metals

    This being said, your advice as well as the op’s regarding wearing a mask is justifiable. Whenever handling dust producing material, a cheap respirator, properly filtered and fitted for the application is always a safe bet. You can’t nor shouldn’t trust that someone else, government agency or corporate interest is looking out for your best interest.

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    Mimikry

    18 days ago

    now I start dreaming again.....
    but I'm afraid the winter in northern Sweden is not friendly to a Pizza oven - that's sad!
    you got my vote!

    1 reply
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    phammy57Mimikry

    Reply 14 days ago

    Thank you for your vote! - I think your oven would survive if you took measures to protect it. Say October time... wrap it in an old blanket and add a plastic cover. Or as one commenter suggests; building a portable base. all the best!

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    CraftAndu

    17 days ago

    Truly awesome! As someone who has also built a pizza oven I reall love this project!

    1 reply
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    leophamCraftAndu

    Reply 15 days ago

    NICE! It's hard work but well worth it when you start eating!

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    AussieAlf

    25 days ago

    That's a fantastic outcome there phammy57.
    Great detailed documentation with your build, job well done.

    1 reply
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    phammy57AussieAlf

    Reply 21 days ago

    Thanks, I'm pleased it's helping people out.

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    mdsidoti

    Question 21 days ago on Step 8

    Hi there, I enjoyed reading through your project. Would have any guess at the weight of the completed dome?
    I'm interested in the possibility of a portable version mounted to an old rolling grill cart and am trying to determine if the cart could support the weight.
    Thanks, Mark

    1 answer
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    phammy57mdsidoti

    Answer 21 days ago

    Hmmm... Tricky one. I have seen someone build a gym ball pizza oven on a wooden base. YouTube I think - I can't remember if it was moveable though.

    It's pretty damn heavy. I could lift the dome easily although it was awkward 25kg, so I'd guess outer verm dome another 25kg, blanket 3kg, plaster layer 15kg, bricks and mortar 20kg, insulation slab 5kg, fire bricks HEAVY! I'd cast a layer of vermiculite to keep the weight down there (it's another technique I've heard of but not as durable) best of luck

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    obillo

    21 days ago on Step 10

    This is so good, phammy57, that I elevate you to the position of Honorary Italian, and therefore render your name in Roman numerals: phammyLVII. You are dead right about the need for FLAME. I'm picky about pizza and every timer I go to Italy, which is pretty often, I consult with local experts about best pizzerias, then visit them and, between bites, seek wisdom. So far, all agree on flames. Inm fact from personal observation I'll say that the flames must not only dance, they must WALTZ. Slowly. Also, the inner walls of the over should be coated in white ash. Again, congratulations.

    1 reply
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    phammy57obillo

    Reply 21 days ago

    Thanks for your kind words from one experienced pizza eater to another ;)

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    DavidL669

    21 days ago

    Very nice. I've been looking at doing the style with bricks as the dome but the ball mold seems easier.

    Question, how long does it take for the oven to heat up?

    How quickly can you do pizza back to back? I have a portable oven and my biggest problem is the stone loosing temps between pizzas.

    3 replies
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    phammy57DavidL669

    Reply 21 days ago

    It takes at least 1 hour to get really pizza hot. You do have to work a bit to keep the fire going which is tricky sometimes when you're also making dough and sauce! It has been known to still be warm in the morning though. Top tips: Very dry logs. Pre heating logs at the opposite side of the oven to the burning fire. Have the door slightly open to draw more air into the fire.

    My dad has a portable oven like yours and whist it heats up really fast it doesn't hold heat as well as this oven. It's due to the density of the materials and their capacity to store heat - hope this helps.

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    DavidL669phammy57

    Reply 21 days ago

    my oven is one of those Unni Pro ovens. Gets really really hot and can cook a pizza in 60-90 seconds... but the stone loses temp between pizzas so I have to let it heat up the stone a bit.... although now I have a gas attachment for it so it seems to work better (only did one round of pizzas).

    But I still want to build one of these!

    Thanks for the reply.

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    phammy57DavidL669

    Reply 21 days ago

    I didn't actually answer the question... Back to back. I put pizzas in one after the other - as fast as people can prepare them!

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    phammy57

    23 days ago on Step 1

    Just to be clear... You need to remove/ excavate some soil to allow for the hardcore and scalpings material. ;)