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.
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!
Oooer,
I have put on the insulation layer and fired in order to dry it out, but I now have a large internal crack in the first layer with some of the insulation poking down through it!
Can I patch this from inside or do I have to take off the insulation around it and patch from the outside….. or doesn’t it matter.
(I’m hoping for option 3).
What do you think Simon?
Pete
I’m suprised that the insulation layer is “poking through”. Did you make sure your oven layer was thick enough. I would be slightly concerned about the crack but I would go for patching the inside and keep going. I doubt it will collapse and should still be fine when it is finished. What materials are you using?
Best wishes
Simon
Simon,
I think a piece about 2″ square fell in from the oven layer.
I have taken some of the insulation layer away and filled from above onto a former I wedged inside the oven and I’m waiting for that to dry at the moment (in the rain). I think it’s stable enough. I am pleased with the insulation layer now it’s dried (wood shavings and clay slip).
I have been using fairly refined clay (I am in Cornwall where they mine the stuff). Outer layer next week, hopefully.
Pete.
Simon,
Great info.
I’m out to insulation layer, how thick should this be, a couple of inches?
I can’t help thinking I should have been doing this before October, but I had trouble finding clay.
TIA
Pete
Hi Pete try and make the insulation layer the same thickness, or thereabouts, as the other layers. As long as we get some dry days, or you can keep the rain off it, I’m sure it will be fine! Best of luck,
Simon
Hi Simon,
I’m hoping to build one of these babies at my folks place in Turkey in November. I’m kind of planning it through in my head now and I’m going to follow your design pretty closely.. I researched plenty of others, but I like your instructions better. Plus yours is cheaper, greener and looks better imo!
I’ve got a few questions (so far!),
1. There’s a pre-existing concrete pad at a decent hight that I’m planning to build on.. my plan was to mortar the bricks directly on to the concrete but I’m wondering about insulating under it though.. you said that you weren’t sure if your bottle layer was necessary or not.. any more thoughts on this? It wouldn’t be hard to do, but just wondering what you though after having completed it?
2. Not sure about getting hold of any wood-shavings over there, but there’s plenty of straw/hay I was planning to use. what do you think? Also what rough ratio did you use for insulating-material:clay in the insulation layer mix?
3. did you end up using all of the sand used for the form in the rest of the project or did you have a load left over?
sorry I forgot to add “please!”
and “thankyou”
Hi James
I think you concrete pad will be fine as it is, without the bottles. If you can’t get hold of wood shavings I’m sure straw/hay will do just fine, after all this is what traditional cob ovens are built from. As for ratio of this mixture I’m afraid I wasn’t that scientific. I recommend making up the clay slip then gradually adding the straw (chopped up) until you have a material which you can form into “bricks”. As you are using straw I also suggest that your slip mixture is less liquid than that used for wood chippings – I think it will bind together better. Finally I did end up using all the sand, that from the former went into the wall mixtures.
Have fun and good luck
Simon
Hi Simon. Great site and lovely oven.
Is the chimney essential? Some references I have seen say it isn’t.
Thanks.
Thanks Martin. I would certainly recommend the chimney – the smoke needs to escape from somewhere!
Cheers
Simon