The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Beginning the rebuild

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Catdog74's picture
Catdog74

Beginning the rebuild

Hi everyone, I am Jen from Australia. I am planning & psyching myself up  for my rebuild, yesterday morning I removed the sand mould from my beautiful ( and extermely labour intensive!) clay oven, obvioulsy too early- asit completely collapsed 4 hours later. I was absolutely devastated, but after having a good cry and feeeling like a right idiot for glossing over the "drying time" part of the instructions, I am ready to start over. I will go through the remnants later today and salvage what I can to re-use. I am thinking I will need to buy more clay to use in the first layer, depending on how well I can salvage and separate the two layers from the remnants. My base is a 1.3 metre wide circular shape built from river rocks and cement mortar- it is nice and sturdy which is great, and I think my clay straw mix insulating base and paver floor are all still intact. I am loathe to take a photo of it in its current collapsed state, the sooner I clean it up ready to rebuild the better!

Yerffej's picture
Yerffej

I have always found that with any new project, there are those things that we know we could do better the second time around.  Often "the second time" never comes about.  In this instance you have been granted a second opportunity almost immediately.  It is great how we never stop learning !!! 

Good luck with round 2...the first one looked really good.

Jeff

Wild-Yeast's picture
Wild-Yeast

Welcome to the ranks of the enlightened.  Failure is the best learning experience and requires persistence to overcome. Glad you decided to marshall your resources for the next round.

More pictures please...,

Wild-Yeast

Catdog74's picture
Catdog74

Hi, thanks for your encouragement! I woke today detrmined to start afresh. I cleaned up the paver base and created the dome using bricks and damp builder's sand. I then added a small amount of clay and water to my clay/sand mix until it passed the drop test. I think that last time my mix was too wet and not clayey enough- most people suggest a mix of 1;1 clay to sand or 1:2, even some say 1:3, however I was usinga dry bagged fireclay, which is quite different altogether to fresh clay, I used a lot less. I think previously my mix was too sandy and this time when doing the drop test I looked for less cracks,and a more cohesive mix. One site said I should be able to throw the clay "bricks": around, and this is what we did, it held it's shape enough to be able to be thrown and still retain the orginal form. The build was nice and fast, thanks to my pre-mixed clay, I spent 5-10 mins preppping each barrowload instead of 30-40 minutes first time around-plus I knew what I was doing ( well, hopefully!). The "bricks"retained their shape far better, I think my previous build's mix was too wet and too sandy. Taking it all apart and storing it yesteardy allowed me to analyse the clay, which had begun to dry out, it just felt too much like sand and fell apart when I moved chunks, it didn't have the charcteristic "stickiness"of clay. I used fireclay for ease of use and availability, and I dodn't think it is as plastic as the clay in my garden for example (I could have dug that up, but faaar too much work for me, I would still be diggging...).

Anyway, so far everything seems positive, my only concern is that I may have gone too far and have made the mix tooo clay rich..I have covered it and will wait several days, cut the door, wait some more till it fells fairly dry (dry enough to support itself), then I will remove sand and light a tiny fire before progressing to building the arch and chimney. Some people suggest doing all the layers at the same time, but I think due to my previous experience and the fact that we have cold winters here, that it is best to let each layer dry first. Also that way I can fix any cracks that appear when drying.My orginal build began last Thursday. In 5 days I hand mixed all of the first layer, did the dome, first layer, hired a cement mixer for the second "cob" layer, laid the second layer, built the arch and chimney, and did the clay plaster final layer, all with the sand dome still inside and sand supporting the chimney/arch. On the 5th day I removed the sand. It all looked great for about 4-5 hours, I lit 2 small fires, but then the entire thing collapsed. Anyway, I will add some photos

Catdog74's picture
Catdog74

The clay stored from last time, under cover and ready to go.

Catdog74's picture
Catdog74

Catdog74's picture
Catdog74

This is slightly smaller and a  much nicer shape than last time. Last one was too pinty at the top, this is more nicely rounded.

Catdog74's picture
Catdog74

The bricks held their shape well, cross your fingers for me!

Catdog74's picture
Catdog74

I read up on the "keystone" shaped final pice, it secures all the other bricks. My previous version had a didgy mish-mash of bricks on top- no wonder it didn't hold. My daughter helped and we meausred as we went to check we had 3 inch thick bricks. That's all for now, I will not have time to work on it again for over a week, so plenty of drying time. We have had some very heavy frosts lately, hopefully the weather holds out and it doesn't get caught up in the freeze/thaw cycle- that couldn't be good for it.

Wild-Yeast's picture
Wild-Yeast

Thanks for the pictures. The new bricks look malleable without being too wet. "It looks about right" is the appropriate phrase, I think, for this point in the build.  Your comment on "frost and freezes" caught my attention. Are you in the Southern, or in the low digit lattitudes in the Northern Hemisphere?

Generally water does not effect the wet clay - if it's been in the ground for millenia and it's gone through countless number of freeze-thaw cycles.  The key to preventing cracks while the clay is drying is to promote even drying. Clay can be dried fairly quickly without cracking if it is dried evenly. The alternative to this is to dry the clay slowly to prevent uneven areas from developing stresses that lead to cracking.  

A good website for information on this is located here:

http://www.ceramicindustry.com/articles/pottery-production-practices-pottery-myths

It covers the drying of clay very well. It also provides information about removing the remaining mechanical water followed by removal of the chemical water at higher temperature. 

Wild-Yeast

Yerffej's picture
Yerffej

I would say that success is just around the corner.  Looks great.

Patience, patience, patience.

Jeff

Catdog74's picture
Catdog74

Hi, okay, it has been a week and a half, and the clay was fairly firm, unable to dent with a thumbprint, with some cracking, so I began work on the arch, the chimney and finally, removed the sand. So far so good! I keep checking out the window to make sure it hasn't fallen down... I can't help being a bit nervous after my last experience! This time around, things look positive- the clay is MUCH MUCH drier and firmer, not rock solid- I am able to blend in the addition of the chimney and arch, but it feels very firm. I used a piece of scrap metal that my husband bent into an arch shape to support the bricks, this gives the arch strength and ensures it will stay put (I hope!). I put the chimney directly into the front of the dome this time, last time it was in the archway, this time around my build is more petite and fits better on the base, with a bit more room for the next layer, and at the entrance, which will be handy. Wild -Yeast, I am in Australia, it is probably far from cold by northern hemisphere standards, we get a lot of beautiful sunny winter days, but they often start of frosty, we had a minus 5 degrees morning last week and snow is forecast in the area today, but most likely won't happen. Inland Australia gets a lot of variation in temperature throughout the day in winter, in can go from below zero to 16 degrees Celsius. I plan on leaving the oven to dry for a week before lighting a fire, today I just lit a few tea lights which gently warmed the interior. Still feeling a bit paranoid- and praying a lot for success! Thanks for your interest!

Catdog74's picture
Catdog74

Building the arch

Yerffej's picture
Yerffej

It looks absolutely wonderful.

Jeff

Janetcook's picture
Janetcook

WoW!

How absolutely lovely!  A very good example of learning from first hand experience.  I have a note on my refrig. that states 'If you don't make mistakes you don't make anything.'  

Thanks so much for the photo diary of your build.  I really liked seeing how this all came into shape.

Take Care,

Janet 

dabrownman's picture
dabrownman

Just beautiful.  Reminds me of something a Palo Soleri student/ teacher would do at Arcostanti. Well done indeed!

Hopefully, you won't need a $20,000 carbon scrubber for the chimney like the EPA wants here - if you tell them you are going to build a wood fired oven and pollute the air in Phoenix in any way.  Heck,  now they won't even let us burn our fire places on Christmas Day here anymore but is fine to burn them when it is 115 F outside.  They can't be that crazy in Australia..... or the end is near!

Catdog74's picture
Catdog74

Hurray! 24 hours later and it is still standing- as I pulled into the driveway after work I steeled myself, but it was still there, firming up nicely and looking great (hiding under a tarp, but still standing!)!!! HURRAYYY!!! I will try a teeny fire next weekend to aid drying, and wait till it is fully dry before adding the insulation layer.

As for local regulations, I don't think it will be an issue,  a lot of people around here have wood fires to heat their homes ( we do) and I really don't think our neighbours will be worried, if they are we will just invite them over for pizza. Sounds crazy dabrownman!

Well, I will update again after the first tiny fire, starting to really believe it will work out okay this time. I want to use it to make pizza, but also to bake breads, and slowcook roasts etc. How thick would you recommend my insulation layer be? The first layer is 3 inches. I was thinking about 3-4 inches thick for the insulation layer. Has anyone here built their own oven and if so, what do you use it for?

Wild-Yeast's picture
Wild-Yeast

What are you using for the insulation layer?

Wild-Yeast

Catdog74's picture
Catdog74

I will be re- using  my previous mix, with  probably a few tweaks, It is sugar cane mulch (like a fine straw), builder's sand and powdered clay, mixed with water. I found the measurements a bit tricky so I went more by the feel than a standard ratio of clay: sand: straw. I think I may need to add more sand to my mix. Is there a "drop test" similar to the one used to test the clay/sand mix in the first layer that I can use for this layer?

 

Wild-Yeast's picture
Wild-Yeast

Do you have a copy of Kiko Denzer's, "Build our Own Earth Oven"? It's the primary source book on building earth ovens. I highly recommend this book.

I'll quote Denzer from page 16:

"My favorite insulation is coarse sawdust - usually free for the taking, or cheap, and easy to use. Mixed with a paint-like mixture of your clay subsoil and water, it will become a workable dough, and will also be heat and fire proof.

Mix clay and water until it's a smooth (non-lumpy) liquid that coats your skin like a very heavy cream (called "slip" by potters). Pour a gallon or two into a wheelbarrow full of sawdust. Mix and knead it thoroughly with the sawdust. Add only as much slip as needed for stiff dough. Pack it around your oven in a layer 2-4 inches thick (you'll need 3-6 buckets full, or 15 gallons)."

Later on page 33:

"Mix up a test batch and make a ball. Let it dry. Is it lightweight, solid and tough? Burn it! It should hold it's shape, but may be fragile and soft."

No sand! Just clay, water and a cellulose filler which will burn out over time leaving a clay like sponge as the insulation layer. He also mentions mulch as an insulating material. Anything consisting of cellulose, close to the size of sawdust, that creates voids in the burnt out clay insulation layer is what you're after. A 3-4 inch insulation layer is fairly standard. 

How fine is the sugarcane straw?...,

Wild-Yeast

Catdog74's picture
Catdog74

Hi, Thanks Wild Yeast. I have been reading your blog, I think I am using a slightly different technique, my straw, sand, clay mix is called "cob". It is an old method of building and houses still stand in Britain made from this method many hundreds of years ago. The sugarcane straw is about 3-4 cms long each strand. I made the base, under my floor from this cob mix and it has held together well. As I write, the fire is burning in the oven. I lit the first fire on Thursday evening, just over two weeks since I built the thermal layer. It was extremely difficult to light and keep alight! I developed a method of home made firelighters (wax & oil melted together and poured into egg cartons). I didn't want to use kerosene based firelighters as they could leave a residue. I have had some shrinkage and cracks, the biggest being between the clay and the bricks of the arch, however I have filled these and they seem to be holding up okay- I think they were just surface cracks. I have since lit a series of tiny fires- about 4 or 5 over the past three days, and a two larger fires ( yesterday up to 125 degrees Celsius, and today up to 175 degrees or 350 farenheit).  The first 3 or 4 fires were barely even warm! Just enough to begin the drying, nice and gentle.The top half of the dome is now dry and very hard. The lower section and arch are still drying and the chimney is also quite dry, the change in colour from damp to dry is quite noticeable. I plan to leave it another week, then hopefully it will be dry enough to begin the  insulation layer of cob. This drying process takes forever! However I am happy that everything is going according to plan and holding up well.

Wild-Yeast's picture
Wild-Yeast

I'm not "Susan" who writes the Wild-Yeast blog.

That's a fair amount of fire. I think you're well on your way to your goal and should be baking before long.

Cob is the term Kiko uses in his book for the sand, clay, straw and water combination. It's a great resource for building an earth oven.  He's got a good section on finishing with a waterproof layer which you'll be getting too after the insulation layer dries.

Are you planning to decorate the exterior?

Wild-Yeast

Catdog74's picture
Catdog74

Hi, Its now two weeks since the insulation layer went on. The oven is pretty dry, except the lower half still hasn't changed colour, though it feels very firm. I fired the oven up at about 9.30 am this morning, it has been going strong for almost two hours, I will give it a bit longer, then attempt a pizza!

 

Catdog74's picture
Catdog74

They worked! We cooked two pizzas successfully. The crust was nice and crispy around the edges ( slightly overdone in spots!) and a bit undercooked -kind of soft and chewy in the middle. The oven was 450 farenheit when we began, though the temperature dropped quite quickly. There was probably too much ash in the oven, so not much room, which meant a bit of ash on the pizza, but it all added to the fun! During the firing, most of the oven has changed colour and dried, so next time should be even better, thanks everyone for your support!

Wild-Yeast's picture
Wild-Yeast

Congratulation! It came out looking great.  And pizza from a your own wood fired oven. Life is good...,

Wild-Yeast