Backyard Permaculture

Clay Pizza Oven - Part 4: The Hearth

2010-07-03T08:18:00.003+10:00

The hearth is the floor of the oven - it is the surface on which the fire will reside and on which pizza and bread will be cooked. It needs to be capable of soaking with high heat (500 degrees c or so), and it needs to be quite flat.

The two main choices tend to be fire brick or clay pavers. Clay pavers (but definitely NOT concrete pavers) are said to last OK, so I bought some second-hand through eBay. I'd much prefer to re-use existing materials, and clay pavers are way cheaper than fire bricks in this country.

Because the Hebel insulating layer was nice and flat, it was easy to lay the hearth pavers directly over the Hebel blocks without any sand in between.

In this oven design, there is a course of pavers sitting upright on their long edge (that is, upright but lengthwise) forming the bottom part of the dome. The dome sits on top of the hearth pavers, so the layout of the hearth pavers will roughly determine the size of the dome. This photo should help illustrate how I laid things out:

My hearth is basically 5 pavers long, by 7 wide and narrows down to 6 wide at the front tunnel. I cut a couple of the hearth pavers at angles so the corners wouldn't project out past the curves of the dome. The photo shows the layer of upright pavers as well; they have been mortared on using high-temperature mortar that can be purchased at places like BBQ shops - I only needed a 1kg tub.

In laying out the pavers and sizing the dome, remember that the dome will be covered in insulation when it's finished - you will have to allow for that thickness.

Clay Pizza Oven - Part 3: Floor Insulation

2010-07-01T21:19:00.004+10:00

One of the most important aspects of this kind of oven is insulation. If you don't insulate the oven it will leak heat, so it will never heat up properly, you will burn immense amounts of wood, and it will become dangerously hot outside. A really well-insulated oven stays cool to the touch outside for hours, and heats up inside quickly.

There are two main kinds of insulation required:

Insulation under the hearth, which is a flat bed of insulation that needs to also bear the weight of the hearth and dome.
Insulation over the dome.

In this post we're talking about the under-hearth insulation. The main options for this are:

Most commonly, a layer about 10cm thick of "vermicrete", which is vermiculite with some cement in around a 5:1 ratio by volume.
A more high-tech option is a board of calcium silicate ("CalSil").
Really low-tech options such as empty bottles embedded in sand or clay.
AAC blocks, marketed in Australia as "Hebel".

I used the Hebel AAC blocks, and totally recommend them for these reasons:

They are made from cement which is aerated; the final block is only about 20% cement (and 80% air).
They are comparatively cheap - $4 each at Bunnings for 600mm x 200mm x 100mm blocks. Since 100mm is a good thickness for the insulation layer, I only needed $64 worth of blocks.
So much quicker to lay than pouring a vermicrete slab - just stick them onto the FC sheet with adhesive, the whole job done in a few minutes.

Here's what they looked like when I put them down:

The Hebel just needs to be treaded with some care: until it's rendered or otherwise covered up, it is very fragile and can chip very, very easily.

Clay Pizza Oven - Part 2: The Base

2010-06-25T23:40:00.004+10:00

Part 2 of the "How to Build a Clay Pizza Oven" series - I built the base from wood for several reasons:

My original location was uneven ground, and it is much easier to make a wooden base with different leg lengths than to pour a new concrete slab.
I had some large timber sleepers lying around, so it represented good re-use.
Timber sleepers are comparatively cheap and can be picked up in the car.
A timber base is quite light - important since my oven ended up on an upstairs deck!

Here's what the base looked like (before it was moved upstairs):

The external size of this is 1600mm long by 1200mm wide. This was originally to accommodate a slightly larger oven dome than I finally went with and also a planned 30cm tiled landing in the front; in retrospect I should really have reduced the base a little. Since I used Hebel blocks on it that were 600x200, a sensible minimum would have been perhaps 1200x1000.

The base is held together with long outdoor screws, and each leg also has a galvanised coach bolt for good measure. It needs to support almost 300kg of oven, so it needs to be very solid. Make sure you can walk around on top of it and not feel any movement at all.

The flat surface on top of which the subsequent layers will be built is simply fibrous cement sheeting (specifically here 6mm tile underlay). This kind of sheeting comes in 1800mm x 1200mm sheets and is easily cut using a "score and snap" technique:

I didn't actually attach the FC sheet to the timber base: the weight of the oven will hold it down, and this way there is less chance of cracking etc. by leaving the oven to "float" on the base.

The costs for this stage were very small; I think the FC sheet is about $20 and I needed about $25 worth of timber. There's probably another $20 worth of fasteners required too.

Clay Pizza Oven - Part 1: Background

2010-06-17T22:23:00.003+10:00

I'm just finishing building my clay pizza oven (AKA cob oven); there's been a fair bit of interest in how it was done, so I'm going to try to document it on here. Here's a shot of my oven, almost complete, for starters:

The basic features are:

Oven dome is made from a clay mix that is formed in place.
Oven is well insulated, both on top and underneath.
The enclosure allows the clay to breathe while being protected from the elements.

I based it on some instructions that were originally featured on Better Homes and Gardens. There is a pdf here, and a video here. If you're planning on building something like this, it's worth getting familiar with those resources. I made the following primary modifications:

One major drawback of the Better Homes and Gardens oven was the location of the chimney inside of the door - meaning you cannot close off the oven for baking unless you set up a mechanism to close off the flue pipe too. I created an entry tunnel and located the flue pipe outside the door area.
A couple of stands were proposed; I used timber (which was cheap, and allowed me to re-use something that was lying around). But whatever base you use, I highly recommend using the Hebel/AAC blocks under the hearth floor for insulation. The decomposed granite/sand combination doesn't seem to be a good idea.
I insulated using a rockwool insulating blanket - more on this later, but it is a great way to insulate.

In subsequent posts I'll try to give some details on each step of the process, along with dimensions and an idea of the costs of things.

Cooking and Making Biochar

2010-02-09T10:32:00.005+10:00

I recently made an EverythingNice Stove - see WorldStove for the free plans.

Ant the Potato King

2009-11-14T14:44:00.002+10:00

The results are in, and Ant has won our potato grow-off by a mile!

Here he is in the photo with his "potato king" crown on, holding his most excellent crop of Kipfler potatoes.

These were the 'taters that we grew under mulch, on top of the old dead grass; now we've got some great Kipflers and an awesome garden bed to start growing lots of other veggies in.

Biochar in Central Africa

2009-10-27T21:28:00.003+10:00

In a comment on my blog, Erich Knight pointed me to the work of "Biochar Fund", who are working in Cameroon with subsistence farmers (apparently trying to survive on under 50c a day).

It seems that they operate out of Belgium, and they are reporting some excellent results. It really does seem that the win/win/win cycle is very feasible - efficient stoves for cooking which also produce char which is used as a valuable agricultural input.

One piece of research that was linked from the Fund website is this trial here in Australia:

We actually harvested that plot this week and we've seen some amazing differences. Its a bit early to give you the exact data at this point in time, but we've seen probably double the biomass production and double the sweet corn yield where we've had high rates of biochar application in the soil. That's somewhere between 10 and 20 tonnes per hectare of biochar. And, yeah, we've had some very, very significant differences in corn production there.

That's really amazing - doubling the corn yield through the application of biochar!

TLUD: Second Attempt

2009-10-25T18:20:00.008+10:00

Yesterday I completed my first TLUD gasifier, built by following Paul Anderson's plans for his "Champion 2008".

Today we gave it a couple more runs, this time using the spines of dry palm fronds chopped by hand into around inch-long pieces. Actually, in the first run they were longer pieces but I kept them shorter for the second, which was more successful.

Here it is loaded up with pieces of frond spines - I put some of the smaller bits on the top:

We broke up a couple of fire starter cubes into bits, and sprinkled them around the top to get even coverage. It lit up well and had a really good flame with very little smoke - our whole family toasted some marshmallows:

It settled into a really nice flame, still with very little smoke:

Towards the end, I started dropping in some big (thick) pieces of palm frond spine; that didn't seem to work too well and it eventually went out with them unburnt. I then blocked up the air (put the lid on the tin which forms the riser, and blocked up the air inlet on the side) - this is what I was left with:

The unburnt pieces are the ones I dropped in later, while it was burning. The rest is excellent char, except for some (bigger) pieces at the bottom; the lowest layer never charred. However, the quality of the char that came from the majority of the material was really good - it was black right through, and snapped really nicely:

So all up, it was a really encouraging result - enormous amounts of heat generated from a few palm fronds, and some great biochar produced. The questions that are still outstanding:

Why didn't the lowest layer of fuel char?
Should I be able to drop pieces in while it is burning? Why didn't those pieces char?
I assume that there was plenty of primary air this time (since the material was quite chunky); is the 90mm secondary air intake too small? What are the symptoms of too little/much primary/secondary air respectively?

I'm looking forward to lots of burning over the coming weeks as we come to terms with this thing!

My First TLUD Completed

2009-10-24T22:36:00.005+10:00

Yesterday I posted about TLUDs and biochar; today I built my first burner, which is Paul Anderson's "Champion 2008" design.

I began with a galv bucket and a 5L fuel can, a 25cm cake tin, a Milo tin, some plumbing fittings, some wire mesh and a few tools.

This is the completed unit, with the lid removed.

I filled it with dry palm fronds that had been through the electric shredder, put a squirt or two of WD40 on top to get things going, and lit it.

Once I put the lid on, the gasification was evident; there was an excellent flame burning at the top and very little smoke evident - huge heat though! Unfortunately the flame didn't last, and things started to smoke so I blocked the air up and then tipped the material out. Quite a lot of the fronds had become char (definitely hadn't burned to ash), but there were a few issues - such as the char front not progressing down the fuel consistently - and the fact that it went out.

From here, I'll be experimenting with different fuels and hopefully get some advice to get the thing burning in the manner I'm sure it's capable.

Intro to TLUD stoves and biochar

2009-10-23T21:04:00.006+10:00

Lately I've become exceedingly interested in the possibilities for the use of TLUD stove technology in what we like to call the "developing world". I'll attempt a brief TLUD definition in a minute - firstly, the problem:

Billions (somewhere between 2 and 3 billion, I believe) of people cook food over solid fuel fires/stoves.
Over a million (between 1.2 and 1.6 million) people die every year from respiratory illnesses related to the smoke from their cooking - mostly women and children.
The harvesting of firewood is a major cause of deforestation.

TLUD stands for Top-Lit Updraft, and in this case it refers to a very basic metal stove structure that functions as a gasifier - the fuel material (which can be quite fine material such as rice hulls) undergoes pyrolysis whereby gas is given off and then burnt, and very useful char is produced.

As I have tried to show in the diagrams, there are huge win-win possibilities in this.

I'm currently constructing my first TLUD stove, and I hope to complete it this weekend. I will then post some more details about it, as well as crediting the guys who have done the great design work on this technology and referencing some more resources.

Resources - Slope

2009-10-12T22:11:00.006+10:00

One of the most important design features in a garden is slope - unfortunately, a lot of gardening methodologies do not deal with this at all. There are heaps of gardening books out there that tell you how to set up a bunch of garden beds and just assume everything's flat.

Even very small-scale earthworks can make a great deal of difference to drainage, water retention, etc. - in my place I had a reasonably minor slope into the back corner of the garden, which was allowing water to run off too readily. Additionally, I wanted to create a really well-drained area for planting a couple of avocado tress. The original slope looked like this:

The soil was really easy to dig by hand - quite sandy, and filled with palm seeds and other plant matter. There were a few other materials around - some rocks and some old concrete from a pathway or something. This is how the slope was modified:

The advantages are:

Excellent drainage for the avocados.
Less water runoff, water infiltrates the terraced soil rather then running down the slope.
Mini swale provides a damper region for a row of lemon grass plants.
Thick mulch of cardboard and palm fronds retains water in the soil.

Potato Progress

2009-09-21T22:16:00.000+10:00

Back in July (winter) I posted about planting no-dig potatoes. This is a bit of an update on progress.

Basically, the plants are looking very strong and healthy but I don't yet know if they're going to actually produce any potatoes.

This is my patch of Nicola potatoes. They were placed on top of the ground, covered with mushroom compost, then composted grass clippings, then shredded palm fronds, then chopped palm fronds, and now sugarcane mulch. I used some palm trunks to create some additional edging beside them to keep the mulch piled up:

This is Ant's patch of Kipfler potatoes. They were planted at the same time and have had similar layers of mulch placed over them. The Kipflers took longer to come up and do not seem to be as vigorous, but perhaps this should be expected for a "gourmet" potato:

Subtropical Fruit Trees

2009-09-20T21:52:00.004+10:00

Living in the subtropics, it makes sense to grow subtropical stuff! A few of the trees that I've put in recently are as follows...

1. Jaboticaba (Myrciaria cauliflora)

This is also known as a Brazilian Grape Tree, as it produces grape-like fruit on the trunk. It will only grow a few metres high and will not bear fruit for quite a few years, but it comes highly recommended and its name is cool. I've never actually tasted the fruit of one of these, although I've seen mature trees growing.

2. Rollinia (Rollinia deliciosa)

The Rollinia is also from Brazil. It is part of the Annonaceae family, which is the funky family that custard apples come from. I've tasted a bunch of related fruits including soursop and sugar apple, but I don't think I've tried one of these yet. It should be bearing within a few years.

3. Black Sapote or Chocolate Pudding Fruit (Diospyros Digyna)

This is actually a persimmon (and not a sapote), but either way it's a really cool fruit. The soft flesh, once accompanied with even a tiny bit of ice cream or similar, tastes amazingly like a chocolate mousse. I've tried it a couple of times and it's really delicious. I tried to grow one years ago - it would seem that they like much more water than I managed to give that one. The one in my current garden has been planted in a slightly low-lying bit of ground where it should get some good water.

Blueberries in Brisbane

2009-08-17T22:08:00.003+10:00

A couple of blueberry plants have just gone in - specifically some low-chill varieties that should hopefully work well in Brisbane. The one in the foreground is a Misty, the one in the background is Sharpe Blue.

Blueberries have a couple of fairly unique requirements - they need an unusually acidic soil (well, "usual" if you live in an ex-pine plantation, but "unusual" for the rest of us), and they are also prone to "fruiting themselves to death" when young - thus I removed all the flowers and berries from these new plants.

As far as soil acidity goes, I haven't ph-tested this garden yet. I planted the blueberries in a barrow-load of compost (apparently made from grass clippings and pine bark) which I expect to be quite acidic, and I've mulched with a mix of palm fronds and tree branches that have been run through the electric shredder. Once it all calms down I'll test the ph.

Sheet Mulching Fruit Trees

2009-08-15T22:55:00.005+10:00

Having started to shape the land and put in some of the most important trees, sheet mulching is a technique that will keep weed numbers down, retain water in the soil, promote soil health, etc. This picture shows the recently-planted mango tree in the corner of the garden prior to mulching:

The sheet mulching involves covering the ground with a continuous layer, in this case old cardboard:

The cardboard will stop all weeds from growing up (until it decomposes), but should still allow water to get to the soil below. The final step in the sheet mulching process is to cover with mulch materials. I'm using palm fronds since there's an abundance of them here, but you could use straw, hay, leaves, woodchip, etc. The approach with the palm frondshas been to use some whole or roughly chopped by hand, as well as running some through the electric shredder. I also planted eight lemongrass plants in a small trench I dug along the curve behind the rocks - they were then mulched with shredded palm frond material. The resultant area currently looks like this:

In the foreground is an avocado ("Reed"), which has undergone the same sheet-mulching treatment. The palm fronds are being weighed down in places by those big, heavy, thick bits that come from the bases of the fronds (don't know if there's a name for them?), and there's a big lump of old concrete which is serving as a stepping stone.

First Produce

2009-08-14T22:15:00.003+10:00

It's always exciting when you start a new garden and first pick something from it. In this case we haven't planted much productive stuff yet, but some of the spent mushroom compost we've been using ($2 per bag, available locally) has been producing some huge mushrooms under some straw mulch. This mushroom is massive - much bigger than my hand. The plan was to make pizza tonight but plans change...

Resources - Sunlight

2009-08-14T22:02:00.003+10:00

Unless you only want to grow mushrooms or maybe ginger, a really productive garden is going to need quite a lot of sunlight. Here in Brisbane the sun can be really intense, so I tend to be wary of exposing anything to "full sun" - it's handy to at least shade the western side a little to allow things to cool down in the afternoon.

Some previous owners of our place had planted trees on the northern (i.e. sunny) side of the garden area, and they were blocking almost of the light. I took out two of these trees and chopped them up for mulch - there's already tons of light starting to get in. I know it looks a bit like a war zone - but it's essential to plan around major resources and in this case light was the first resource that had to be made available.

The new design will feature large productive trees (such as avocado and mango) toward the back, with smaller plants in front of them. It can be hard to picture what things might be like once the plants mature, but it's important to do so - whoever planted those trees in the first place obviously had no thought as to how much the sun would be blocked once they grew.

Sources of Mulch

2009-07-24T18:27:00.006+10:00

I've been investigating the sources of mulch already on our property:

Palm Fronds: I was told by a relative that these are bad things and that you should pay to have them collected and disposed of. Quite the contrary, I'm finding them to be amazingly useful. I just use some long-handled "loppers" and cut them up into bits. The only part I haven't found a use of is the thick, wide part where the frond peels off from the tree.
Cardboard: There's a reasonable stack of cardboard here; from either old moving cartons that didn't survive our move, and from a couple of large items we purchased.
Composted grass: The previous owners dumped all of their grass down the back corner - it's now an interesting mix of compost, dried grass, and certain other rubbish. Unfortunately they left an oil-change pan in there - I'm hoping it wasn't full of old motor oil! Also, I've got a compost tumbler which works really well.
Trees: There are some trees that are blocking the sun and really need to be thinned out (and/or removed). Some of the thinner branches may run through the electric mulcher.
Leaves and stuff: There are a bunch of leaves to sweep up, as well as clippings from pruning the front hedge.

Looks like a fairly good basis for getting the new garden going, although we'll have to bring in some material as well. The ongoing plan is then to try to generate more mulch on-site:

Fast-growing, nitrogen-fixing trees like pigeon pea and crotalaria.
Nutrient-rich leaves such as comfrey.
Grass such as lemon grass.

Bargain Trees

2009-07-16T21:20:00.006+10:00

Last weekend I dropped in to our local Bunnings to see if they might, by some unlikely chance, have some Nitrogen Fixing Trees (NFT's) in stock. Check out the bargains I scored!

Yes - that's a reduction from $129- to $20- - and I picked up two really big (like 9 foot high) Cassia Fistula trees in 45 litre bags. It was a nightmare to get them through to the checkouts, out to the car, and to get them into the car and home - but worth it.

We planted one of the trees in the front of the house. This corner of the house gets way too much sun, and tends to get too hot even in the winter. We needed a large, fast-growing tree to try to get some shade ASAP - and an advanced Cassia Fistula is just the thing! Here's Ant helping plant it (the tree goes way off the top of the frame of the photo):

The second treet got planted down near the back fence. The plan for that tree:

Nitrogen-fixing for the soil. I plan to prune it fairly regularly and heavily which should induce a die-back and subsequent regrowth of the root zone, releasing nitrogen in the process.
As material for mulch; a fast-growing tree like this produces a lot of biomass which is ideal to "chop n drop".
As a potential support for passionfruit vine. I've found leguminous trees to work really well in that way in the past.
To attract bees - it will look like this when it flowers.
To improve privacy as we start to thin out the existing trees which are on the northern side of the garden area and blocking all of the light.

Primary downside is that the seedpods are poisonous to chickens (which we don't yet have, but will probably come soon).

No-Dig Potatoes

2009-07-14T23:04:00.004+10:00

We've decided to kick things off in our new garden by planting some potatoes using a no-dig method. Here's Ant with his batch of seed potatoes lined up in a careful grid on top of the ground:

Our plan is to lay the seed potatoes on top of the existing ground (two fairly flat areas of quite compacted soil with some dead grass on it), cover each potato with a small pile of mushroom compost (available cheaply at the local mushroom farm), then pile on composted gras clippings (already on site) and then to continue to pile on mulch as the plants begin to grow.

On the other side of the garden, here is my batch with a small pile of mushroom compost on top of each one:

If mushroom compost is in fact a bit alakaline (I think it is?), it should alleviate the need to put down lime on the ground first.

We're trying to grow two different varieties of potato this season: Ant's batch are Kipfler - a distinctive long, thin potato that are perfect for potato pizza. My batch are Nicola - Looking forward to comparing how they each grow and what they're like to cook and eat.

Beginning a Permaculture Garden

2009-07-14T22:31:00.000+10:00

How exciting - the first post on our new blog! This is the beginning of our new garden; right now, it's a pretty bare chunk of land hidden behind a few trees (mostly palms). There's a garden shed down there, a few old paths covered with pebbles, and some concrete edging around what must have once been garden beds.

In the photo above you can see that our dog Roxy (a miniature foxie) quite enjoys running around down there, but it's really quite bare: there's a single lemon tree (complete with citrus gall wasps in the branches) which bore a single lemon on it this season, and palm trees galore.

The second photo shows how heavily shaded this part of the backyard is; a row of trees has been planted to separate it from the lawn area - however this row of trees blocks all of the sunlight. There are some great jobs coming up:

Start to plant potatoes under mulch on some bare patches of ground right away. The goal will be to get some kind of crop and to start to improve the soil a bit at the same time.
Some minor earth works to create small swales and some terracing to improve water harvesting and reduce runoff down the slope.
Let some more light in by pruning (and possibly removing) some of the existing trees.
Determine the most effective way to chop up existing foliage for use as mulch.
Find local sources of cheap mulch to bring in to start things off.
Start ordering some seeds and other planting material ready for the spring.