Novice clay build

[martynw]

Hello

I've started building a clay oven, so far Ive got the base/plinth up which wasn't too stressful. I had a bit of help from more practically minded people. I will need help along the way so any constructive comments are welcome!

First question, how do I add photos to the thread ( I'm using my I phone)

[martynw]

[martynw]

Ok so apologies for not posting progress pictures along the way, but here are the developments

[martynw]

, I added a layer of fabric to keep the sand in, a layer of old pricks that were knocking about and then filled with sand leaving 75mil for the cal sil board and fire bricks, we then cut the bricks to the size of the internal measurements ( this took a long time) then build the sand former. I did the done and archway with chimney all in one, though I'm a little worried I won't be able to reach in to get the sand out. It's been resting a couple of days but as the weather has been rubbish it doesn't look to have hardened very much at all. Intend to remove some of the former this weekend and try some small fires to fire the clay at least on the inside.

[oblertone]

I'm sure that's a typo, but the rest of your endeavours look first class. Building the entry arch at the same time will limit your access, but it's done now so crack on. Some folk have used tea lights to harden the inner face during a phased excavation; as to actually reaching the back of the oven why not pop into your local builders merchant for a roofing strap. I use one for general fire/ember management at very little cost.

[martynw]

Just laughed out loud! It was bricks!!!!

[martynw]

I had left my sand former in around a week, simply because I didn't have any time to remove the sand. I took half out then gave it a few hours with tea lights, I then removed the rest and gave it a couple of hours of a small fire burning, I did the same today just keeping a small fire ticking away, the clay is starting to dry out and harden and there is a few cracks.

One of the main issues is that my archway seems to have separated from the clay and there is a gap now I need to fill. Any ideas??

The other thing is that it's fairly clear that I don't have an even thickness throughout, I can tell because of the varying temperatures on the outside of the dome. Can I just add more clay to even this out??

I think I know the answer to this but, do I have to wait until the first layer is fully dry and hardened before adding the insulation ( I'm doing a fibre blanket covered in vermiculite ) ??

Lastly how much does it matter about cracking on the inside of the oven, I can't really see inside there, and not all the newspaper has burnt away yet, but it's going to be very difficult to reach in to patch bits up on the inside.

P.s took the advice about a roofing strap, perfect tool for scooping sand and moving the fire about!!

[oblertone]

My (limited) knowledge of clay ovens are that cracks are dealt with by the application of fresh clay, but also that they are fairly inevitable; so I'd seal the one between the dome and arch in just the same way. The oven will dry out quicker without an insulation layer, in fact I used my bare dome for a year without insulating it; not that I'd recommend such a course but it worked fine.

[martynw]

[martynw]

Hello,

since the the last update I had added another layer of clay to fill in any cracks, I had done some small curing fires and all seemed to be going well but then my archway began to fall down as you can see from the pictures, I have now added my insulation blanket and vermicrete layer, but have since taken the archway down as I was told the engineering bricks I used were too heavy and as they are not porous the mortar won't stick to them. I've bought some lighter boring bricks, and am thinking an opening supported by a metal lintel might be best, this is obviously an area where it helps to have some brick laying skills.

[martynw]

[zelige]

The flat arch is certainly one way to go - I used it for a festival oven at Glastonbury. When I did my arch on the clay oven in the garden I used engineering bricks (the ones with the the holes through them). By passing several lengths of copper wire right through the bricks' holes and packing with cement I created a reinforced arch still standing 5 years on.

[martynw]

I gave the oven its first proper spin today, cooked a pizza which was cool however, there were what I can only describe as tiny explosions causing bits of clay on the inside to come off, the bits were like less than a centimetre thick and varying sizes.  This was happening as the fire got bigger, I am now very worried. I am going to patch up with fresh clay in the areas I can reach. The inside of my oven is not smooth at all, you can feel where all the clay "bricks" are is this an issue?

There were also some parts of the vermicrete layer that got very hot, is this hot air forcing its way out of the oven??

any advice appreciated 

[downunderdave]

Dec 4, 2016 17:58:27 GMT martynw said:

I gave the oven its first proper spin today, cooked a pizza which was cool however, there were what I can only describe as tiny explosions causing bits of clay on the inside to come off, the bits were like less than a centimetre thick and varying sizes.  This was happening as the fire got bigger, I am now very worried. I am going to patch up with fresh clay in the areas I can reach. The inside of my oven is not smooth at all, you can feel where all the clay "bricks" are is this an issue?

There were also some parts of the vermicrete layer that got very hot, is this hot air forcing its way out of the oven??

any advice appreciated 

What you describe is known as steam spalling and is caused by moisture turning suddenly into steam. As the steam rapidly expands it forces the clay wall apart. Water volume increases 1640 times when it turns to steam. The remedy is to tease the water out with gentle fires. Try to avoid any direct flame impingement on the surface. If you see steam, back off you're going at it too hard. You may think it's dry but there will still be moisture in the middle of the clay walls. Try throwing some sheet plastic over the oven. The condensation on the under side will tell you there is still moisture present. The oven needs to be fully dry before before building any big fires.