Monday, 28 July 2014

Cob Oven Building

This is a slight diversion from my usual posts. Some of you may have seen on Instagram that I've spent the weekend building a cob oven! I've been fascinated by cob for a quite a while, I bought the book Shelter (all Lloyd Kahn's books are great!) as a teenager and it's been a method I've wanted to try ever since. It's a very ancient method of cooking, in Mexico it was called a Horno and used for cooking Adobe bread, made with honey. In Hungary it was called a Kemence and is shaped like the instrument of the same name.  I  love to cook and loved the idea of being able to do so outside (partly inspired by this amazing place). I really do love to spend time outside, even when it's raining! I think it's probably as a result of a childhood spent making mud pies (or choc chow as I called it) and dens. Anyway when I moved in to my new home I suddenly realised I could build a cob oven in my back yard! By some miracle like happening the same week that I had this thought I saw a poster for a cob oven building workshop at Camp Kernow in my local health shop. It was meant to be! My mum and I went on the one day course in May and learnt SO much. It was incredibly hard graft, we helped construct an oven that would cater for 40 children, but it was great fun.

Our yard conveniently already had a structure on which we could site the oven (this saved us a lot of work!) To begin with we levelled our plinth out with builders sand and layed out 18 firebricks (these are what keep the oven hot). We then chalked a circle in the centre (this marks the inside of the oven) and made sure that everything was level.

Next we worked out the height of the inside and exterior and marked it on a pole. We held the pole in place whilst building a sand former using damp builders sand. We used the chalk markings (we changed the size slightly from the first picture!) and the markings on the pole to get the shape. We did have quite a lot of trouble as it kept collapsing because our sand wasn't wet enough, we got there in the end though.

We then covered the sand former with 3 layers of wet newspaper, we mixed ours with little pva to help it stick (you can also use wallpaper paste). It's pretty tricky this stage as the newspaper has a tendency to fall off.

 Next up was the first layer of cob! We used a mixture of Clay that we sourced from the bank above our mosaic and subsoil from B&Q. The mix is supposed to be 80% subsoil/aggregate and 20% clay and some water to get the correct consistency, it shouldn't be too wet or too dry. We mixed ours on a large tarpaulin but you could do it straight on the floor!  It's a pretty messy job so I got my wellies on for this bit. It's also very tiring (I think people usually spend a lot more time on cob ovens and have more than two people constructing it hah!) After mixing each batch I made sausage shapes and my mum built them around the sand former. This layer should be around 3 inches thick (although this will vary with the size of your oven). My mum kept spritzing it with water as she went and making sure there were no cracks or holes.

Once the first layer was finished we scored it with a knife to create a key for the next layer. We covered it with a tarpaulin. The next day we began the second layer. This is pretty much the same as the first but you add straw to the cob mix (it helps strengthen it and add insulation) and make it slightly thicker (4"). 

Having finished the second layer we removed the pole and stopped the hole with a clay sausage.

We just have to wait for it to dry and then we can cut the door and render it! 

As you can see it's been a lot of work, I definitely wouldn't approach this task lightly but the results are well worth it. I can't wait to try cooking in it.

If you'd like to read more about cob have a look at these books:

Building with Cob: A Step by Step Guide by Adam Weismann & Katy Bryce

Shelter by Lloyd Kahn 

Homework by Lloyd Kahn

Tiny Homes by Lloyd Kahn

Also have a look at these sites:



  1. That is amazing, have always wanted one myself. Looks like you two did a fantastic job, can't wait till it dries :))) xx

  2. So, not only do we get a rather brilliant step by step guide to cob oven building here, we also get a wonderfully intriguing glimpse into the corner of your garden, with the vibrant mosaic wall.
    It's like I said in my recent post, I love getting to see other people's gardens.

  3. What a cool project! I can't wait to see how it looks all finished!

  4. Perfect timing, I've been talking about doing this in our garden for ages. The on-line tutorials look very dull and off-putting and you've managed to build yours colourfully and dressed well. i want one. xxx

  5. How exciting, an outdoor oven. Cannot wait to see it finished. I have friends that made a similar thing in their garden, I would love to build one. I have a clay chiminea at the moment. Your garden looks so lovely and colourful, just like you!

  6. A Beautiful Garden with so much Color... and having an Outdoor Oven will be Wonderful! Dawn... The Bohemian

  7. It's fab! the food you cook will taste amazing, I've always fancied outdoor cooking (that doesn't include my bucket bbq) I love your garden! x x x

  8. oh my goodness what an undertaking I'm so impressed! That back wall is a work of art, did you guys do that? I could spend some quality time in that rainbow garden! I think the best part is seeing you and your mom do this together, what a labor of love!

  9. Haha! Love your little dance :) this is a great diversion. It's lovely to see your home taking shape. I've never really given much thought to cob ovens, but I think I could get interested. Do show us what you end up cooking? Xxx