3. The Clay-Sand Mixture and Puddling Technique

So now the fun begins!  Before I get on to detailed instructions of how to build the oven I want to provide some details on preparing the all important building material – the sand-clay mixture.

Ingredients

  • Builders sand
  • Clay
  • Water (optional)

Equipment

  • Shovel
  • Bucket
  • Tarpaulin
  • Thick plastic bags
  • Wheelbarrow
  • Wellington or other sturdy boots
  • Legs!

You can buy builders sand from any building suppliers, some garden centres and DIY stores (e.g. B&Q). Either buy it in individual plastic bags or get a job-lot delivered – you will use quite a lot.  

What type of clay should I use?

I have had quite a few questions about the type of clay to use.  As far as I know you can use any type of clay you can get your hands on.  I dug my clay from a local farmer’s field here in Hampshire (clay overlying Upper Cretaceous chalk if you are geologically minded – maybe Paleogene?).  The team at River Cottage get theirs from a pond on site, in Dorset (I think it is Blue Lias).  If you can’t find any clay locally you could always buy potters clay which would be wonderfully homogeneous – free from large particulate matter.  Which reminds me, try to get clay does not contain too many stones – they are liable to form the focus of cracks in your oven if left in the mixture.  

Quantities

The ratio of clay to sand is 1:2 (one part clay to two parts sand).  I used a bucket as a convenient measure and found that one bag of builders sand almost filled two buckets which was nice!  

I think it is wise to make-up just enough mixture (with a little bit extra) to complete one layer of your oven at a time.  Why?  Well if you make up a huge batch (enough to complete your oven) it could dry out before you get a chance to use it if you get delays between layers (if it rains for example).  So how much do you need for one layer?  This will vary depending on the size of your oven.  For mine, if we define one “batch” as two buckets of sand mixed with one bucket of clay, the first (oven) layer took three batches (6 sand to 3 clay).  This left enough over to fill small cracks after drying and to begin building the chimney.  The outer layer required more mixture because it is covered a larger surface area.  I used four and a half batches for this layer.

Mixing or Puddling

Clay chunks distributed onto sand ready for puddling.

Clay chunks distributed onto sand ready for puddling.

Mixing the clay and sand is by far the most tedious part of the whole build process.  What you are trying to achieve is a well-mixed material with no pockets of unmixed sand or clay and the only way to do this seems to be by using your feet.  The process is known as puddling and it goes like this:

 

  1. Spread a tarpaulin out on a firm surface (double it over in case you get holes in it).  
  2. Tip two buckets of sand in a pile onto the tarpaulin and spread out a little.  
  3. Next, fill another bucket with clay.
  4. Take a chunk of clay and break it into small pieces (thumb sized) and distribute them over the surface of the sand (like throwing broken-up pieces of mozzarella onto a pizza base!).  Take this opportunity to dispose of any stones or sticks you might find in the clay.
  5. Puddling Sand-Clay mixture with help from my dog Scout!

    Puddling Sand-Clay mixture with help from my dog Scout!

    Wearing your boots, start to mix the sand using your feet (puddling).  The best technique is to tread and twist.  I recommend putting some music on and get into the groove! Seriously, you will look pretty daft doing this but you need to twist – Chubby Checker sty-lee!  This is where a group of friends come in very handy.  Many feet make light work of puddling sand and clay.  It is great exercise though so keep reminding yourself how much good it is doing you when you start to get knackered and bored!

  6. Keep mixing until the clay lumps have disappeared then add more clay chunks and get back to puddling.
  7. Keep repeating this until the bucket of the clay is mixed into the sand.

I found it takes somewhere between 45 minutes to 1 hour to mix one batch.  One tip I discovered which speeds things up is make sure the sand is damp before you start mixing.  It definitely helps the clay mix in better (essentially you are coating sand grains with clay and water helps break down the clay bonds I assume?).  Add some water before hand if you need to but dont go mad with it!

The last thing you need to do is check that the mixture is of the correct consistency i.e. not to wet and not too dry.  You might be surprised at how sandy the mixture seems but this is how it is meant to be.  The team at River Cottage HQ had a great method for testing the consistency though which I will share with you.  

  1. Sand - clay ball after drop test.  It held together just right!

    Sand - clay ball after drop test. It held together just right!

    Grab a handful of mixture and form a ball about the size of a lime.  

  2. Hold your arm directly out in front of your body at shoulder height.  
  3. Drop the clay-sand ball onto hard ground in front of you.

The ball should hold together quite coherently.  If it splats flat the mixture is too wet and you should add more sand to dry it out a little.  If the ball breaks to pieces (explodes) it is too dry and you can add a little water.  Simple!

Once you are happy that your mixture is just right shovel it into a thick plastic bag to keep it moist while you mix the next batch.

If you are ready to start building your first layer I recommend shoveling the final batch into a wheelbarrow for ease of use.  Wheel it over to your plinth – it’s time to start building your oven!

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106 thoughts on “3. The Clay-Sand Mixture and Puddling Technique

  1. I’ve read a lot of different opinions on what type of sand to use in the clay/sand mix. Arguments for sharp sand suggest it’s stronger and that builders sound is too rounded and so won’t lock together to give the dome it’s strength. Any thoughts?

  2. Hi Simon,
    I like your webpage and the way you’ve systematically covered the construction of the owen.
    In two weeks I am going to a scouts camp where we will build one such owen. So far I’ve built one such few years ago and last year I’ve doug out two owens from the loess wall – and 80 pizzas on the camp in 2 hours were most memmorable for kids. Now I want I have a challange for me: I need to build one during few days. I will have bunch of feet on my disposal and helping hands during the building. After that it will stay on site (to which we will not return after the camp is over). Having that in mind, I also need it not to be that much durable (1 week will be ok).
    I also have a problem with obtaining the clay, but we have loess in abundance. Since loess is in a way simmilar to clay and people from this region have been building their houses for centuries from bricks made from loess mixed with straw, I plan to use it for construction instead of the clay. The insulation layer is going to be loess+straw or sawdust. What do you think – what mixture would be best for inner and outer layers? 1:1 loess:sand or even 2:1? (since it is more “sandy” than clay) I’ve already built one from loess, but am not sure if I made it too “sandy” by using 2 parts sand and 1 parth loess.

  3. I found clay on my property that has pea size and larger stones in it. I prepared it by spreading it out in trays to dry. Once dry I pounded the particles with a rubber mallet to break it up. I put a measured volume of the dry clay in a 5-gallon bucket and added enough water to make a slurry using a paint stirrer with a drill. I poured the slurry through a 1/4 inch screen to remove the stones and debris. I then added two volumes of sand and again used the paint stirrer to make a uniform mixture. The mixture was pured into trays and allowed to dry sufficient to use for the oven. This way I had a uniform mixture and did not have to use the puddling method.

    • That’s what I did too. Except I didn’t dried the clay and pulverized it. I was impatient so I immediately added water to it and made a slurry (it was difficult to do since fresh clay doesn’t dissolve well in water). But still, this is way more easier to do than puddling. Damp clay is already hard to mix with water, how much more with sand.

  4. Find this site verry helpfull ? Im in flaorida not much clay around i purched bags of fire clay will this work with the same ratios or not at all

    • I am curious how you made out with this. I too am in Florida and am trying to figure out the correct ratios. I have seen recommendations for as high as 1:7 clay to sand (1:4 seems most common). I think that since the purchased potters fire clay is pure, you would use more sand. I would love to hear from someone who has done this to see what real world experience says. This makes a big difference in how much you spend for the project (sand in FL is practically free).

      • I have always found 2:1 (or 2.5:1 or 3:1) as best. It depends upon the water content of the clay BUT if you have too much sand it becomes very difficult to build with.

  5. is there any chance I could use ready grogged clay instead of adding sand to avoid the puddling technique or do you think that wont work? thank you
    p.s. your websire is so helpful for my school project 🙂

  6. Great thanks for the info. overcast here in eastern Canada but i’m tired of waiting. i’ll make the mud and hopefully will build later on this week. Cheers!

  7. Simon, any idea of how long you can store the sand/clay mixture? I’m trying to come up with some wood for the plinth, and we’re looking at some rainy weather for the next week, but i’d like to have the clay ready to go. Would a week be too long to have the clay ready? will it harden if it’s tied up in plastic bags?

    • If you keep it covered, i.e. out of direct sun light, it’ll keep for ages. If it does dry out a little, add some water and leave it to hydrate for half a day or so! I used a bag recently that had been sat in my garden for over a year.

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