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The Golden Spiral & it’s Application in Natural Building ∞ DIY Wood-Fired Pizza & Hot Smoking Earth Oven
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The Golden Spiral & it’s Application in Natural Building ∞ DIY Wood-Fired Pizza & Hot Smoking Earth Oven

Uses for this oven include:

  • Pizza
  • Baked goods.
  • Smoked products.
  • Dehydrated food.
  • Activated charcoal (burn wood in a sealed tin).
  • Pottery or glass kiln (this oven can reach up to 800°C).
  • Hot water.
  • Get creative!

This article discusses how to plan, build & use a wood-fired oven using locally sourced natural materials.

CONTENTS:

THE PLAN:

  1. Project background & aims.
  2. Design & dimensions:
    • Wood-fired oven.
    • The base.
  3. Collect, prepare & use natural building materials.

THE BUILD:

  1. The base:
    • Earthbags.
    • Gabion basket.
    • Foundation.
  2. Wood-fired oven:
    1. Build a hemisphere out of wet sand.
    2. Position the door.
    3. Cover with clay-earth & allow to dry.
    4. Open the door & remove the sand mould.

USING THE OVEN:

  1. First fire.
  2. Wood choices.
  3. Sustainable wood sources.
  4. Care & maintenance.

THE PLAN:

Project background & aims…

In August 2019, Noosa Forest Retreat hosted a ‘Permaculture Design Certificate’ (PDC) course & ‘Permaculture Practical’ in succession.  The permaculture designs created during the PDC inspired this project which was constructed during the ‘Permaculture Practical’.

Aims:

  • To support community spirit by developing a communal space (to bring people together around a pizza oven).
  • To build with locally sourced natural materials.
  • To construct a wood-fired pizza oven as a team (hierarchy-free).

Design & dimensions:

…wood-fired oven…

The wood-fired oven is an earthen chamber which once hot, acts as a thermal mass.  As a result, cooking continues even when the fire & it’s coals have been removed.  Because the strongest shape is an arch, it makes sense to use a hemisphere for the oven chamber.  This also ensures heating is uniform.  But how deep & high should the oven chamber be?

This is dependent on how many pizzas we need.  At the permaculture community ‘Noosa Forest Retreat’ – around three people will cook on a weekly basis & around thirty during a PDC course.  Thus, the oven needs to supply from 2 – 30 pizzas.  Let’s work this out.

At full heat (» 400°C) our oven will cook pizza in 90 seconds.  If we give a leisurely 3 mins to cook & transfer one pizza in/out of the oven:

1 pizza oven:                      30 peeps x 3min = 90 minutes    …hungry customers.

2 pizza oven:                      30 peeps x 3min = 45 minutes    …PIZZA-PERFECT !

For the Noosa Forest Retreat build – we need a two pizza oven.  A large pizza is around 30cm diameter.  Leave 5cm spacing for each side.

2 pizza x (5cm + 30cm + 5cm) =  the cooking surface needs to be 80cm diameter.

The cooking surface is a circle with a diameter of 80cm.  Because the oven chamber is a hemisphere, to find the height- we calculate the radius.  ½ diameter = radius.  ½ x 80cm = 40cm.  The oven height is 40cm.

So far….we have the dimensions of the oven chamber = hemisphere:

80cm across & 40cm heigh

We need to get the pizza inside the cooking chamber – we need a door.  But, what dimensions should we use?  Let’s try observing nature.  When we observe smoke, we see it spiral as it rises.  Let’s use this spiral shape to calculate the door’s dimensions.  This should also maximize our oven’s efficiency.  This makes sense, because permaculture is about using intelligent design to work with, not against nature.  When it comes to a wood-fired oven, this means managing fire to harness heat.

(1)

We’ll use the Golden Spiral because it describes the dynamics of ‘energy’ responsible for harmony and order in the universe (2).  It is created using the Fibonacci Sequence, which is adding neighbouring numbers together in sequence = 0, 1, 1, 2, 3, 5, 8….

0 + 1 = 1

1 + 1 = 2

1 + 2 = 3

2 + 3 = 5

3 + 5 = 8

…forming squares & building into a spiral.

(3)

(4)

The spirals’ universal principle of organisation is in the proportion of the larger square relative to the entire rectangle – it is always 61.8% (5).  Above this point, the hot smoke spiral condenses.  Below this point is the oxygen feed.  Seems like a sensible place to put the door.  Door height = 61.8% x 40cm » 25cm.  But how do you make a door?  At Noosa Forest Retreat, the oven door was cut from a hardwood tree trunk – however, it is also possible to use an old cabinet door with handle attached (just remember to remove the paint from the cooking side).

Design & Dimensions:

…the base…

The oven needs to sit at the correct height to make transferring pizzas in & out easy.  Let’s again draw our knowledge from nature’s design tool, the Golden Spiral.  If the average person is around 175cm tall, then their waist height is (61.8% x 175cm) » 110cm.  Our base needs to be 110cm high (off the ground).

(6)

But what about the width & depth of the base?  So far, we have the oven chamber’s dimensions = 80cm across.  Let’s assume the oven walls are around 20cm thick.  This makes (20cm + 80cm + 20cm) = 120cm square.

Collect, Prepare & Use Natural Building Materials…

As much as possible, source materials on-site…

  • Earth.
  • Sand.
  • Water.
  • Fibre (straw, cut grass, dried leaves etc).
  • Wood (bamboo, logs, thatch etc.)
  • Stone.
  • Natural dyes (mulberry fruit, ochre coloured clays etc).
  • Living plants.
  • Landform features (existing rocks, hillside etc).
  • Reuse materials (everything builds!).

At Noosa Forest Retreat, the wood-fired oven chamber & the sides of it’s base were formed out of cob material.  It was created by mixing together…

CLAY = the binder which holds all the material together.

SAND = provides strength & stability.

DRIED BANANA LEAVES = provides tensile strength between layers (like rebar in concrete).

WATER = helps to activate the clay & hold the mixture together.

Clayey soils were found on a hillside (next to where a dam & dirt road had been dug).  Sand found on a creek bank contained too much silt – ‘cleaner’ sand was brought from offsite.  Banana trees were pruned to collect the dried leaves.  Rainwater was collected via a tank.

Because soil is unique to each location – there is no standard in making cob material.  Finding the correct ratio comes through trial & error – by creating trial ‘bricks’.  This also helps familiarize the build team with the medium.

Trial mix:

  1. Start with 1:1 (clay:sand) & no fibre.
  2. Add water until pliable.
  3. Form a brick and set aside to dry.

Repeat the ‘trial mix’ a number of times with variations:

  • Add less/more clay
  • Add less/more sand
  • Add less/more fibre (dried banana leaves for the Noosa Forest Retreat build)

Leave the bricks to dry.  This may take anywhere between 4hrs – 24hrs, depending on the season & climate.

The best mix is identified by the absence of cracks & a strength test via compressing between the hands.

Mixing technique:

  • place materials on a piece of black plastic
  • combine the materials together by standing, stomping & dancing on the mixture (use your feet)!
  • flip the mix upside-down by pulling the edge of the plastic upwards.
  • when a ball of the mixture will stick to a wall ‘like glue’ – it’s ready!

Tips:

  • for high clay soils, use around 2:1 (sand:clay)
  • use as little water as possible.
  • clay shrinks as it dries, to prevent cracks add organic material & sand.
  • label each brick to keep track of the ratios.

APPLYING THE MIX:

Knit the cob material together by poking holes with your fingers.  This will mesh the fibre within together.

  1. First layer:
    1. Form a ball of the mixture and place in position.
    2. Add another ball (the same size) next to the first.
    3. Work your way all around the bottom (horizontal) row.
    4. Move up & create the next row.
    5. Continue all the way up to complete the first layer.
  2. Second layer:
    1. Repeat steps above.
  3. Third layer:
    1. Omit fibre to provide a smooth finish.
    2. Decorate:
      1. sculpt the cob material.
      2. add decorative pieces (crystals, rocks etc).

THE BUILD:

The Base – Earthbags:

  1. FILL BAGS WITH EARTH. Do not treat or change the earth – use it as is.  These bags were collected as scrap from a local plant nursery & farm.  Any material that will not decompose is suitable as fill (including waste materials).
  2. Once filled with earth, SEAL THE BAG by folding the end & ‘sewing’ with tie wire.  To make piercing the bag easier, cut the wire on an angle to create a sharp point.
  3. TAMP …using a homemade tamper (right) or store-bought tamper (left). To create a homemade tamper – fill a bucket with concrete & set a pole into the middle.  A flat rock is also suitable for small builds (such as this project).  Don’t forget to lift with your knees – not with your back!

(Steps 1 & 2)

The Base – Gabion Basket:

  1. STABILIZE CORNERS …using star pickets or similar.
  2. CREATE BASKET …by wrapping with & securing mesh.
  3. FILL …with rocks & earth. Any material that will not decompose is suitable as fill (including waste materials).
  4. Provide extra strength to the top of the gabion basket (which will eventually become the cooking surface) by leveling & securing inflexible mesh with small holes.
  5. Cover with cob mix. [See “THE PLAN – Collect, prepare & use natural building materials”.]

(Step 1)

(Steps 2 & 3)

(Step 4)

Foundations:

Earthen materials will dissolve if allowed to sit in water for an extended period.  To ensure water does not pool – dig a drainage channel around the entire base which connects to lower ground.  Fill the channel with gravel to ensure easy water flow.  Rainwater will fall into the channel and flow to lower ground before it hits the base.  Check for silt after heavy rains & maintain with a regular schedule.  If a part of the base does dissolve or need patching – mix some earth material & fix!

Wood-Fired Oven:

  1. CREATE THE COOKING SURFACE …by laying kiln-fired material (pavers, bricks etc). Ensure it is level to  prevent the topping from sliding off the pizza.
  2. MARK OUT THE OVEN CHAMBER WITH ROPE …by holding one end in the centre & moving the other end around in a circle. To mark out the correct dimensions, ensure the rope length equals the oven chamber radius (= 40cm).
  3. SHAPE & MOULD THE OVEN CHAMBER …into a hemisphere using wet sand. Use the length of rope to check the height is correct.  Cover in wet newspaper to stop sand from sticking to the oven roof (& later, falling into the food).
  4. PLACE THE DOOR.
  5. BUILD THE OVEN CHAMBER …by layering cob material (up to three layers). The thicker the better – this is the oven’s thermal mass.  [See “THE PLAN – Collect, prepare & use natural building materials”.]
  6. DECORATE the final layer. [See “THE PLAN – Collect, prepare & use natural building materials”.]
  7. ALLOW TIME TO DRY. Do not cover.
  8. REMOVE THE SAND MOULD …gently remove the door & dig the sand out. Don’t forget to also remove the newspaper – if it is left behind, sand which has stuck to it will fall into the pizza.

(Step 1)

(Steps 3 & 4)

(Step 5)

(Step 6)

(Step 8)

USNG YOUR OVEN:

First Fire…

Start with a small fire & gradually build it larger & larger.  This will ensure any moisture remaining in the earthen material will move out slowly.  Once dry, it will take around two hours to reach full temperature » 400°C.  The oven can be used at lower temperatures if desired.  A candy thermometer (which can tolerate high heat) may help until you are familiar with using the oven – do not place it directly into the fire.

Because the oven walls act as a thermal mass, they will regulate the temperature & keep it steady (even if the fire is removed).  Removing the fire provides additional cooking space.  When the food cooks, moisture will move out through the oven walls – the oven will ‘breathe’.

For cooking – remove the door completely.  For smoking, open the door halfway.  This design does not have a chimney – smoke will vent through the front opening.

Wood Choices…

One of the star attractions to using a wood-fired oven is the smoky flavour.  Hardwoods with low sap work best.  Also, wood from fruit & nut trees.  It is even possible to use herbs & dried plant materials to add a customized flavour!  This chart helps identify which species will provide the most ideal flavour for what you are cooking in Australia.

(7)

But not all wood is suitable.  Any processed wood (paint, varnish, glue etc) is toxic and should never be used.  Also avoid: oleander, pine, camphor, mulga, milky mangrove, laburnum, poison walnut etc.  To discuss this topic further, see ‘Wood Allergies & Toxicity’ at The Wood Database (online):

www.wood-database.com/wood-articles/wood-allergies-and-toxicity/

Sustainable Wood Sources…

Felling trees is not sustainable & time to dry can be extremely time consuming (years for full grown hardwoods).  Pruning into coppice provides a sustainable alternative & allows the plant to live out it’s full term.  Simply cut the tree into a stump and allow multiple new shoots to grow.  Harvest these shoots as your firewood.  Allow them one month to dry, before placing in the wood-fired oven.  Having multiple plants dedicated to this purpose will provide a sustainable – life friendly wood source.

(8)

Care & Maintenance…

  • PROTECT FROM RAIN …keep covered until a roof can be built (ie. use a tarp).
  • DO NOT SEAL …waterproof finishes (concrete, paint etc) will trap water vapour inside where it will condense in the earthen wall, causing it to soften & collapse. When cooking, moisture in the food will move out through the oven walls – the oven will ‘breathe’.
  • SHUT THE DOOR …to prevent animals nesting inside when not in use.
  • COVER YOUR FIREWOOD …keep it dry!

∞ THANK YOU ∞

Team members:

  • Jo Richards
  • Ben Forbes
  • Leon Peterson
  • Guillaume Chaillot
  • Paola Tazzer
  • Thomas Lanotte
  • Chrissy Laurikainen (project creator, facilitator & foreperson).

Additional help:

  • Ian Wilson
  • Tanya Madgwick
  • Diane Cinelli
  • Ian Trew
  • Drew Kilburn
  • The WWOOF crew
  • The Peterson family

Cover image (left):  Standing (L to R) Chrissy Laurikainen, Jo Richards, Ben Forbes, Leon Peterson & Guillaume Chaillot.  Sitting (L to R) Paola Tazzer, Lani Peterson & Thomas Lanotte.

References:

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About The Author

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About The Author

Chrissy-Tiina Laurikainen

In person + online permaculture teacher. Online permaculture consultant. Upkeep of a 30 acre rural property (using permaculture & other agroecological techniques). A communal research laboratory focusing on free innovation in the works. Doing what I can to support LIFE on planet Earth!!

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