6. The Insulation Layer

Entrance dry? Chimney dry? Great! Let’s start building the next layer – the insulation layer.

What you’ll need:

  • Some clay
  • Some wood shavings
  • Some water
  • A bucket
  • A wheelbarrow
  • A spade
  • A power drill and plaster mixer (optional)
The insulation layer complete.

The insulation layer complete.

First thing you are going to do is make a clay slip which is simply clay mixed with water. The simplest way to do this is to put some water in a bucket and slowly add chunks of clay, squashing, squeezing and mixing with your hands as you go. Alternatively you could add water to half a bucket of clay and leave it to soak for a couple of days. You could then squish-up the clay quite easily.  You are aiming for a consistency similar to that of thin natural yogurt.  

I spent quote a long time making my slip until I discovered a short-cut method using a drill and plaster mixer. It works really well but is very messy! Chuck your clay and water in a large bucket (or large bin) and blitz it with the mixer.  Job done!

Next throw some wood shavings into a wheelbarrow. I bought a huge bag of wood shavings from a local pet shop and I still have three-quarters left (any takers?). Add some of the clay slip and mix well with a spade or get your hands dirty. The mixture should be wet enough to form “bricks” similar to those you made for the clay-sand layer.

Build up the insulation layer using exactly the same technique as before. Simple! Leave it to dry and then you can move on to the last step in the build – woo hoo!


68 thoughts on “6. The Insulation Layer

  1. Hello Simon Thanks for all your information I have a question — I am waiting for the first layer to dry. For the insulating layer can I use vermiculite left over from building the plinth instead of wood shavings ? Thanks Jen

  2. Hi Again,

    I have just made my first batch of clay sand mix and made the first layer of my oven.

    It struck me that in your repairs you added chicken wire/mesh in the repairs to add more structure.

    Would it work if i added this to the insulation layer to make it more structurally sound?

    Just an idea 🙂

  3. Hi Simon

    I’m wondering how long I need to leave the insulation layer to dry. The delicious article implies a few hours is sufficient. I have built the plinth and plan to lay the bricks tonight. My planned schedule from there is:
    Day 1: sand former for dome, puddling, construct initial layer
    Day 2: cut out entrance. Dry the dome. Light a fire.
    Day 3: Light another fire
    Day 4 maybe light another fire. Do chimney, entrance and insulation layer. Dry overnight.
    Day 5: Build final layer of oven.

    Is this feasible? Should I leave longer in between layers? I’m just itching to get it all done, but don’t want to compromise quality.


  4. Hi Simon we are in the middle of making our clay oven. The first layer we think had too much sand in it and had a quite a few cracks. The second layer, I note you say to just use clay and wood shavings but we have put sand in too but with a higher proportion of clay than the first layer. This layer too has a large crack? We in the north west of England and clay oven is shaded for most of the day but gets the sun at the end of the day. With the last layer we noticed that the whole clay oven appears to have lifted, crack formed around the junction with base. So my questions will these cracks affect the oven? should we put four layers on in case the first layer collapses? How do we repair the crack at junction of base? Will the sand in the insulation layer affect the oven? Lastly should each layer be independent or should they stick together? Many thanks

    • Hi Karen

      these ovens will crack – don’t panic. If they dry out too quickly, they’ll crack. If you have too much clay to san in the mix, they’ll crack. If they get super hot (which they will), they will expand and crack. Basically, you just need to keep plugging any cracks with extra sand:clay mix as you go, and the oven should be fine.

      I would NOT put on four layers – there is no point. Re the crack at the base, just fill it best you can with clay:sand. Each layer should stick together but I guess you will get a natural separation between the layers because of the fact they dried between construction of each.

      I hope this helps.


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