When building a clay oven one has many choices as far as clay is concerned. You can dig up your yard (or your neighbour’s yard!), buy moist clay from a pottery supply or you can buy dry, powdered clay.

Even though the soil where I live is high in clay content, and even though Simon has done an excellent job in describing the puddling technique for mixing moist clay/soil and sand, there are those who like me, look for the easiest way possible because, well, because we’re lazy!

In reading Simon’s blog and doing research on other Internet sites and books, I slowly formed an opinion about how I would go about building my own oven. I settled on using dry powdered clay for the following reasons:

1)      I believe a consistent mix of clay and sand can be achieve.

2)      I can do so with less effort than puddling moist clay or soil with sand.

3)      I will not have to worry about stones and rocks as I would if I dug up my garden. Rocks and stones need to be taken out of any soil you dig up, as they become focal points for weaknesses leading to cracks! It is a fact of life that all clay ovens will develop cracks, I posit that we don’t need to encourage them!

So with that in mind, I decided to experiment before taking the plunge into buying tons of powdered clay.

The first thing I did was to make three batches of clay and sand with different ratios of sand to clay. For this purpose I decided to use what is known in the US as builder’s sand. This is sand of varying size granules and of irregular shape. It is not playground sand, nor is it “paver” sand which are sieved and sorted so that they are very smooth and almost powdery. Some paver sands are also treated with polymers and the like, and I have no desire to find out how this will affect the mix.

The clay I used is a Redart brand terracotta. It has no grog or other additives, it is simply powdered clay with a talcum powder consistency.

I prepared a batch of 3 parts by volume sand to one part clay, 3 to 2 and 2 to 1 as well. The idea being to find which ratio shrank least while conserving the desired qualities of strength, workability and able to pass the “drop test”.

I baked the different bricks at 200 F (93 C) for about 6 hours in my kitchen, and left others out to dry inside the house due to the unusual amount of rainy days around here (two weeks of rain, which is very unusual!) In doing so I came to the following conclusions:

The 3 parts sand to two part clay ratio gave the best performance, given that there was hardly any measurable shrinkage. I observed 1/16th of an inch over 3 inches (1.6 mm over 76.2 mm) (roughly 2%)  and it remained very workable when mixing and when forming. It passes the drop test and hardens satisfactorily.

The other ratios either shrank more, the 2:1 shrinking almost 6 %, or did not do well on the drop test as was the case for the 3:1 ratio.

So, now that I had determined the best ratio of sand to clay, I went about mixing a bigger batch that would approximate the batches I would need when it came time to build the oven itself.

For this purpose, I found it easier to mix it up in a mortar pan. These are made of plastic and are sold at home improvement stores here in the US. They are rectangular bins where you can mix the equivalent of 50 kg of cement or mortar. To mix I used a hoe, a shovel and my hands! I have read where some have used a cement mixer for this, but I found that my way worked for me and I didn’t have to rent a mixer! If you do have one handy, try it, but I really don’t see the need to go out of your way to have one!

The procedure is really very simple. Lay out the sand in the pan, put the clay evenly over it and mix well. The key is how moist is the sand you are working with! In my particular case the sand I was using was pretty moist to begin with (2 weeks of rain will do that!).  Using the hoe or shovel, mix the clay and sand very well, until you are sure that there are no pockets of either, nor any large clumps. If the sand you are working with is very dry, then wet it until it is fairly moist, as if building a sand castle at the shore.

As you mix the sand and clay you will notice it achieves the consistency and look of dry oatmeal.

Once the mix is ready, pour water a little at a time and mix. You do not want to pour too much at once, or you will find yourself adding sand and clay so go slowly with this!

I start out using the hoe and shovel, but eventually you will see the point where you need to use your hands to ensure consistency. Feel free to use your feet if you think that works better and you wish to save money on a pedicure!

The eBook is available for sale at the bargain price of £2.99 from my new super-duper website:

http://www.clayovenbook.co.uk

I am also excited to say that you can now download the book for your Kindle, iPod Touch, iPhone or iPad directly from Amazon’s Kindle Store. Just follow the link below:

http://www.amazon.co.uk/Build-traditional-wood-fired-Step–ebook/

Enjoy the book and please leave comments to let me know what you think.

Best wishes and happy building.

Yes it’s true; I have been a bad clay oven owner. Earlier this year I uncovered my oven for the first time since putting it to bed for the winter. It had sustained some water damage as usual (the tarp I used was clearly not totally impermeable to the UK winter rain and snow) but on the whole it wasn’t looking too bad. After the first firing of the year (pizzas) I left the oven to cool down over night with the intention of covering it up again the next day. Then it rained. The following day it rained again, and then again and again for several days – heavily! I know I should have covered it up after the first night but to be honest I had lots going on at the time and just didn’t bother. After a couple of weeks I made a decision to leave the oven uncovered so I could see what happened, a sort of oven-sadistic experiment if you will. And so it has remained open to the elements for several months now.

So what have I learned? Firstly the oven has not collapsed. The internal structure seems still to be sound. There are some cracks but none of them appear to permeate to any great depth from the internal layer outwards. Externally the picture is slightly worse. The rain has partly eroded some of the clay:sand mixture from the outer layer creating a rough texture which is rather friable when touched. This only seems superficial though. There are a few cracks but this is not unusual. The chimney has suffered somewhat, with a large chunk falling out of one side. The other, most noticeable sign of damage is at the interface between the bricks of the oven entrance and the external side wall of the oven. Clearly, water has run down this natural channel and eroded some of the mixture.

So is it ruined? Is it time to knock it down and start again? Well no, I don’t think so! I fired the oven up for a large party two weeks ago and it worked just perfectly. I cooked pizza for over fifty guests over a period of six hours and the oven performed as brilliantly as it always does. It’s fine – seriously.

This experiment has demonstrated to me that the ovens are much hardier than I had imagined. I don’t recommend that you leave your oven unprotected (I will do some repair work and re-cover mine soon) but if, for whatever reason, you do forget to cover it and it gets wet, it should not lead to disastrous consequences.

By the way, if there is a Society for the Prevention of Cruelty to Clay Ovens (SPCC) I am deeply sorry. I promise it will never happen again Your Honour.

* No ovens were hurt during the making of this post.

An overview of the damage. Note the build-up of sand, around the base, eroded from the sides.

Detail of erosion along the brick-sidewall interface

A sad looking chimney

Apart from a few rain showers, I think everyone had a good day – I certainly did. I’ll be running two courses next year so book early because they seem to sell-out quite quickly. Below are some photos from Saturday’s course.

The Oven at the Sustainability Centre

You'll be making one of these.

Last year I ran a one day clay oven building course at the Petersfield Sustainability Centre which is near my home in Hampshire, UK.  About 20 people turned-up on a beautiful, sunny, summers day and, under my supervision, constructed a clay oven like the one featured on this blog. The Sustainability Centre have their own, permanent oven on site, so for lunch all the participants made and cooked their own pizzas.  A fabulous day was had by all (even though I do say so myself!).

I’m pleased to say that I am running the course again this year on Saturday 18th June (2011).  If you’d like to come along, you can find more details on the Sustainability Centre’s website.  Here’s the link:

http://www.sustainability-centre.org/courses_adult_detail.php?id=30

Maybe I’ll see you in June?

Simon

Clay Powder*

A question that I commonly get asked on the clay oven blog relates to the process of mixing the clay:sand mixture used to build these ovens.  I learnt how to prepare this mixture by using wet clay and mixing it into the sand using an old fashioned technique called puddling (I believe the Roman’s used this same technique for mixing material for their villa floors – they used things like dung, soil and cows blood though!!).

You will find a post on how this is done here:

http://clayoven.wordpress.com/2008/09/04/3-the-clay-sand-mixture-and-puddling-technique/

Puddling is effective but rather laborious and time consuming. Many suggestions have been made by visitors to this blog from using cement mixers to industrial hand “blenders”.  The problem is that clay and sand don’t really like to mix unless they are ground together using the puddling technique.

One commenter suggested drying out the clay first, grinding it and then adding it to dry sand and water in a cement mixer.  Technically a potentially useful solution but in practice, drying and grinding clay to powder would be a nightmare and would likely take much longer than getting your feet dirty, puddling.

This week I have had a few conversations with blog visitors Steve O’Conner and Dori who inform me that one can purchase bags of dry, powdered clay.  Dori said:

“Ive actually used the powdered stuff to build my oven – bags of FireClay (which was also called mortar clay in my store). We first did the tarp and dance method where we poured all of our ingredients on a tarp and stomped on them, but eventually used a cement mixer which was much faster. What ive learned from the powdered stuff is that you need a MUCH higher ratio of sand:clay then the lumpy stuff. Pure clay in powdered form shrinks quite a bit. Other then that, it has worked just fine for me.”

Well I never knew this but it sounds like a great alternative to puddling to me!  I will try some experiments later in the year to see what ratios one needs exactly.

In the mean time, if you try it out, please be sure to share the details on here.  Thanks for the info chaps!

Simon

*Image taken from http://www.starwest-botanicals.com/images/D/210106-51.jpg

Earlier this week Katharina posted a message on the blog to share the story of an amazing clay oven she and a group of friends have built in Finland.  They have christened him Archie!

Archie was built as part of a project called “5″ which, in Katharina’s words is:

“to inspire thought about culture, identity, and the objects we consume, with a shared experience of eating. Food as an ephemeral product, consumed by our very own bodies, represents an everyday experience that connects people and memories. We are what we eat – so who are we?”

All good stuff I’m sure you’ll agree!  What I really love about this project though is the fact that most of the volunteers who came together to build the oven had never met before.  I believe that most of them had heard about the project through online social networks and decided to get involved out of curiosity and a shared passion for food and the issues of local food production/ food security.

The other astonishing thing is that the oven is built in a very urban area of Finland which goes to show that clay ovens have a place in cities as well as rural areas.

Katharina has pulled together a blog and uploaded lots of photos so please have a look, be inspired and send her and the team some clay oven love!

The Blog: http://1234viisi.wordpress.com/
The photos: http://picasaweb.google.de/105277324473045859094

Archie with his makers

The video is a 20 minute epic so I have split it into two parts in order to squeeze it into YouTube.  You might need headphones to hear all of the commentary.  Enjoy!

Part One

Part Two

I know have to patch cracks and fix the chimney.  Hopefully she’ll be OK for another year once I get these repairs underway.  We shall see!

The project is called the Quartet Community Allotment Garden which is part of a broader inititiave called Quartet in the Community, “a partnership of Margate schools and children’s centres, working to improve the lives of children and the community[1]“.   The allotment project is the brainchild of Nicola Wood, a senior extended schools coordinator at Hartsdown Technology College, a secondary school in Margate.  The partnership received £3,000 from the Kent Criminal Justice Board, “as part of a national programme to use ill gotten gains, confiscated from crooks, to fund worthwhile community projects[1]“.

The money is being used to tackle the problem of youths loitering in the streets outside the homes of older people, causing friction and antisocial behaviour. A new group will be set up to bring older members of the allotment and the local community together with young people to work together at the allotment, pass on their knowledge and build relationships. The idea has been backed by the local Police Community Support Officers (PCSOs)…who believe this scheme will help to bridge the gap between the generations in the area.[2]

The Community Allotment Garden is now developing nicely.  Over several weekends, local young people have worked together with members of an existing over 50′s gardening group to get the allotment going.

So where do I come in?  Well a few weeks ago Nicola stumbled upon this blog and asked if I will like to help facilitate the building of a clay oven on the plot.  I just couldn’t say no!  I really love the idea of the project and so will be spending the next three weekends on-site helping the group to build their own oven.  I think it will be great fun and if it helps to bring these seemingly disparate groups of people (the old and young) closer together then that’s a fabulous bonus.

Last weekend Nicola and her team of helpers started the oven project by building the plinth and oven floor following instructions from this blog.  On Saturday we will be puddling lots of clay/sand in order to build the first layer and, if we have time, the oven entrance and chimney.  The final two weekends will then be dedicated to adding insulation and building the final layer, hopefully leaving time to fire the oven up for a transgenerational pizza party!

1: http://www.thanet.gov.uk/pdf.aspx?page=11799&template=PRpdf

2: http://cashback.cjsonline.gov.uk/cc.asp?area=19