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Old 07-12-2013, 07:33 AM
Peasant
 
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Location: Lennox Head, NSW, Australia
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Default First time 41" clay/homebrew oven.

After writing this I realized I had rambled on a bit. I have put some questions at the end, seperated from my waffle, if that helps

************************************************** *******
On and off for the last 2 weeks I have been constructing my first pizza oven. I did a course with Alan Watt just over 2 weeks ago which gave me the motivation to get started. This also lead me to FB which has made the whole build more interesting to say the least.

So far I have put about $300 dollars into the build using a combo of stuff I had lying around and purchased materials.

I will post photos later but just wanted to start this thread as I had been putting it off.

I used some "common" bricks I had removed from my house during a reno and set about building my base under a reasonably new awning at the rear of my house. I had considered the flue but didn't realize it would finish so close to the ceiling. I will probably have to put a bit more time into this sooner rather than later.

The brick base ended up being just over 1300mm square. I put an 8mm bar across the front plus one across the middle with 2 more courses of bricks on each. I had never laid bricks before so this took a fair while, constantly checking that I was square and level. I think it turned out okay. I used a mix of 5 sand to 1 cement and a splash of Bycol in my water. The sand wasn't brickies sand so it had no clay. I don't know if this will cause the sky to fall, but we will see.

At the course we used a 12mm sheet of fibre cement for the base. I opted for a sandwich of 6mm board plus two layers of 3mm or 4mm making up 12mm to 14mm. I wavered between something like this and a slab. I hope it won't come back and bite me.

On top of this I placed a layer of 12 600x200x50mm Hebel blocks. I wanted something a bit deeper, say 75mm or 100mm but they only had the 50. I feel I may have let down the insulate, insulate, insulate motto here.

Next I loose layed some 230x115x40 clay pavers. I opted for blonde ones as they are apparently higher is something that makes them tolerate a little bit more heat (it may have been aluminium silicate but I only just overheard it at the course). Mine had rounded edges on both flat faces so when I laid them they left little valleys. I had a sort of brain snap and spread some of the homebrew high heat mortar (3:1:1:1 - sand:cement:lime:fireclay) mortar into these valleys and sponged them down pretty well. I hope after firing it will harden right up and avoid crunchy bottoms on my pizza.

I chose to create my dome floating around my floor. I used some of the mortar from above to fill up the big gaps around the edges rather than cut down some pavers (I ended up cutting some of the pavers down later and realized how easy it was with a diamond blade so probably should have filled these big triangular gaps with cut pavers).

I popped cardboard inside my soldier course (are they still soldiers when they stand on their sides rather than their ends?) and underneath it to try and keep it floating. I smooshed a bit of mortar around the outside of these soldiers as I had a bit left, but not much. This was done half heartedly as I knew the dome would hold them in place.

I then went about molding up the sand dome. The sand was wet from an earlier shower which made it really easy to mold. I did fuss over this a little. I got my half avocado/pear shape. I covered this with newspaper that I dipped in a bit of clayey water that was sitting in a bucket from an earlier process.

After much research, reading, coffees, head scratching and beer I ended up going with a 3:2:1:1 - sand:fireclay:cement:lime mix for my dome. This was a bit of a combo of the high heat mortar from FB, the mix used at the workshop I did and some ebook clay oven recipe. I figured more clay is better and lime will stand up to the heat better. I think I read on the "brickless on a shoestring" thread here that using the high heat mortar for the dome is uncharted territory. And as I didn't use a "reo" structure I was in even deeper (or at least different) water so why not change the recipe and see what happens.

When I mixed the stuff up I made sure the kids weren't in breathing distance (not so much care for myself). But I did let them help me put it on the sand mould. I stopped this when the lime got into a cut on my hand and turned the skin black. Those little burns are still stinging like a "you know what." Luckily the kids missed out on any chemical burns. I will wear gloves next time and the kids will need to have the full complement (gloves, eyes and mask) if they want to help with lime and or cement work.

I put this on as little squished pancakes, about an inch thick (probably more like 30mm), overlapping each other. I think this layer may have ended up being 30mm to 40mm. Part of the way through a crack formed but I feel this was just the weight of material causing a separation. Needless to say I patched it up.

I'm thinking I will need to put another, slightly thinner layer on to take my dome thickness up to around 40mm to 50mm. From what I can work out if my floor is 40mm thick then my floor needs to be somewhere between 40mm and 80mm or some such. I believe there needs to be balance between the thermal layers.

I finished up this layer around 5pm and around 2am remembered that I forgot to put my flue in. Luckily the dome wasn't too hard, more crumbly. I got a serrated knife out and started scratching out the circle for my flue. Got it in with a pretty snug fit. Regardless if I go for another layer of thermal mass I will need to give this a much better housing.

Just now I pulled the door mold out and started removing sand. The dome didn't collapse so that is a good thing.

I did a quick measure and found my door ratio fell in a big hole.
flue output inside the dome: 290mm
door height: 230mm
door width: 520mm
dome height: 520mm

So flue output to dome height is 55%;
door height to dome height is 44%; and
door height to flue output height is 80%.

The magic ~63% is GONE! I cut my door mould to 300mm being just about right. However I think the door moving let the sand settle and dropped the roof level somewhat. There is a lot of thickness at the door opening, probably 50mm or so.

I still plan on putting a 100mm or so vermicultie/perlite or sawdust insulatng layer on top of this. Plus I want to start curing the dome. I don't know if I want to start small fires before or after I put the insulating layer on and need to go and do some more research (after posting this).

************************************************** ***
If anybody is still there after my novel of a post I have a few questions:

* For a floor thermal thickness of 40mm is the dome thickness of 30mm to 40mm enough or should I thicken it up a bit more? Maybe take it up to 50mm to 60mm?

* Should I grind the door opening back up as high as possible? I could probably get up to around the flue output of 290mm.
Attached Thumbnails
First time 41" clay/homebrew oven.-01-img_1808.jpg   First time 41" clay/homebrew oven.-02-img_1823.jpg   First time 41" clay/homebrew oven.-03-img_1825.jpg   First time 41" clay/homebrew oven.-07-img_1848.jpg  

Last edited by sandybits; 07-13-2013 at 01:28 AM.
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Old 07-12-2013, 11:26 AM
Gulf's Avatar
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Join Date: Sep 2011
Location: Mississippi
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Default Re: First time 41" clay/homebrew oven.

Wow, that is a lot to try and absorb at one reading. Without pics I probably did not follow it very close. But, before you go much further, you might want to check out what some other FB forum members comments about the Alan Watt design. I hope that it conforms more to the FB design than it did a few years ago.

Check this one out (Heat bank filler).

I may be wrong about this particular design. I hope Brickie will chime in on the subject. Brickie's first build was after taking an Alan Watt course I think. His is the second reply to the above thread.
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Last edited by Gulf; 07-12-2013 at 11:34 AM.
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Old 07-12-2013, 02:48 PM
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Location: brisbane australia
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Default Re: First time 41" clay/homebrew oven.

Gudday Sandbits
I think you have yourself a working oven there. Something's may not be best practice but workable none the less.
On your dome/hearth floor thickness you should find that enough mass to work well enough. Me I would be more concerned in insulating the dome to keep the heat in. The pealite/ cement would be best option by far. Most nowadays seem to insulate before curing in an effort to minimize cracking. Yes you will get cracks to some degree all ovens have them regardless.
On the oven entry to dome height. The 63 per cent is you best ratio it's the optimum . But 55 should workable . If you can adjust it without wreaking anything why not.
I would like to see some pics of your work. Open up the message window, click on the paper lip icon next to the smily face icon. The box that opens will allow you to first find a photo then click the Upload tab. Max of 5 photos. Close the box and check the paper clip tab again . It should contain your photos
Regards dave
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Old 07-12-2013, 03:31 PM
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Default Re: First time 41" clay/homebrew oven.

Dont worry Sandybits your oven will work.

I liken the Alan Watt oven method to like getting your first car, you use it and abuse it until you see all the faults in the car, then you trade up to a better model.

I was quiet happy with my Alan Watt until I found this here forum, I saw a better way to build an oven so I knocked it over and built a proper oven.
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Old 07-12-2013, 06:21 PM
Peasant
 
Join Date: Jul 2013
Location: Lennox Head, NSW, Australia
Posts: 31
Default Re: First time 41" clay/homebrew oven.

Thanks for the replies. And I apologise once again for the big chunk of text. I'll throw some photos into the mix this afternoon.

After ddoing thevcourse i found this forum and, based on reading here, I eliminated my proposed heat bank.

I think if this is my first car (mine only went 80km/hr and that was downhill, leaning forward and pushing on the steering wheel so there was no burnouts or circle work) then I won't invest too much more into it. I'll grab a bag of perlite and insulate that sucker and be done with it.

I felt I wanted to get everything perfect first go which kept me scratching my head. Then I realised these thing can be made out of mud, so any little improvement should help.

I haven't got a lot more than time invested so far so not to worry.

I'm off to try and do my first burnout, ahhhh, curing fire . Thanks again.

Last edited by sandybits; 07-13-2013 at 01:57 AM. Reason: Wife iPad corrected everything
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Old 07-13-2013, 01:27 AM
Peasant
 
Join Date: Jul 2013
Location: Lennox Head, NSW, Australia
Posts: 31
Default Re: First time 41" clay/homebrew oven.

I just added some photos to the original post.

I have added some more pics to this post. The first one shows some cracking and the lime and sand (1:1) wash I painted on to try and fix it. I haven't even fired it yet. It happened when I tried to remove the flue as I thought it might get stuck in the wrong position. Another crack, about 500mm long, ran across the dome from the flue which I also painted over.

The 2nd photo shows the big chunk that came out of the opening when the crack occurred. The opening really thickened up as my door shifted loosening the sand allowing it to be pressed down as I put the dome on. I was planning on taking the diamond blade to it later once it hardened up a bit anyway. The opening is probably 70mm thich, narrowing down to about 40mm back towards the flue.

The 3rd photo shows the finished thermal layer of the dome. I put on a 10mm to 15mm thick layer of aggregate:clay:sand:lime:cement (1:1:1:1:1). The aggregate, clay and some sand was a pile of stuff I had used for a path.

So this should take my thermal layer to around 50mm. I also built up around the flue to give it a bit more support.

I lit a piece of paper and threw it in there to see what the flue does but the smoke just swirled around the top of the dome before going out the opening. I don;t think this means too much, though.

I need to organise some dry kindling to light some small fires and grab a bag of perlite or get some saw dust for the insulation layer. It might be just as easy to buy the perlite for $26 for the 100 litre bag.
Attached Thumbnails
First time 41" clay/homebrew oven.-12-img_1868.jpg   First time 41" clay/homebrew oven.-10-img_1861.jpg   First time 41" clay/homebrew oven.-09-img_1855.jpg  
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Old 07-13-2013, 02:05 AM
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Thumbs up Re: First time 41" clay/homebrew oven.

Quote:
Originally Posted by sandybits View Post
I just added some photos to the original post.

I have added some more pics to this post. The first one shows some cracking and the lime and sand (1:1) wash I painted on to try and fix it. I haven't even fired it yet. It happened when I tried to remove the flue as I thought it might get stuck in the wrong position. Another crack, about 500mm long, ran across the dome from the flue which I also painted over.

The 2nd photo shows the big chunk that came out of the opening when the crack occurred. The opening really thickened up as my door shifted loosening the sand allowing it to be pressed down as I put the dome on. I was planning on taking the diamond blade to it later once it hardened up a bit anyway. The opening is probably 70mm thich, narrowing down to about 40mm back towards the flue.

The 3rd photo shows the finished thermal layer of the dome. I put on a 10mm to 15mm thick layer of aggregate:clay:sand:lime:cement (1:1:1:1:1). The aggregate, clay and some sand was a pile of stuff I had used for a path.

So this should take my thermal layer to around 50mm. I also built up around the flue to give it a bit more support.

I lit a piece of paper and threw it in there to see what the flue does but the smoke just swirled around the top of the dome before going out the opening. I don;t think this means too much, though.

I need to organise some dry kindling to light some small fires and grab a bag of perlite or get some saw dust for the insulation layer. It might be just as easy to buy the perlite for $26 for the 100 litre bag.
Gudday
Be patient I know about the Allen Watt wkend were the low tec clay get dried out and fired that wkend. Don't be temped that Portland cement has to at least go off properly and the moisture start to come off the oven before you fire it.
You piece of paper experiment does prove something your oven sounds to me like it draws alright. When you light a cold oven you get a difined layer of smoke which lingers for a while till the walls start reflecting the heat back and the smoke disappears or really gets burnt fully.
Time to do some more investigation on oven curing there's a whole section on oven curing in the forum
By the way that's a nice looking oven
Regards dave
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Old 07-13-2013, 04:36 AM
Peasant
 
Join Date: Jul 2013
Location: Lennox Head, NSW, Australia
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Default Re: First time 41" clay/homebrew oven.

Quote:
Originally Posted by cobblerdave View Post
Gudday
Be patient I know about the Allen Watt wkend were the low tec clay get dried out and fired that wkend. Don't be temped that Portland cement has to at least go off properly and the moisture start to come off the oven before you fire it.
You piece of paper experiment does prove something your oven sounds to me like it draws alright. When you light a cold oven you get a difined layer of smoke which lingers for a while till the walls start reflecting the heat back and the smoke disappears or really gets burnt fully.
Time to do some more investigation on oven curing there's a whole section on oven curing in the forum
By the way that's a nice looking oven
Regards dave
My vague idea about working with concrete (slabs mind you) was that you wanted to keep it moist so it cures harder (or stronger). And my gut is telling me to just leave it for a few days to a week.

Thanks for the feedback on the "piece of paper" experiment. The way the smoke swirled around looked awesome.

I wonder if you can tell much about a person by how they build an oven? The fact that mine fits the basic shape but is a bit rough around the edges says a lot about me Thanks for the compliment.

The kids are all tucked in and now its time to learn about curing.

Thanks again, Dave.
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Old 07-14-2013, 08:05 AM
Peasant
 
Join Date: Jul 2013
Location: Lennox Head, NSW, Australia
Posts: 31
Default Re: First time 41" clay/homebrew oven.

I'm going to let the oven dry out for a few days to a week before starting the curing process (as per the stickied thread here somewhere).

I'm still a bit unsure of whether to insulate before or after I cure the oven. Need to do some more reading on this but the consensus seems to be to insulate before curing.

I am scratching my head about how to dampen my flue. The workshop built oven had the flue inside the chamber and had a hinged cap that sat at the top of the flue. This had a chain attached so you could set the cap at whatever level between closed and open you wanted. When I asked the guy at my local BBQs Galore he told me that these were illegal. I'm not sure if he misunderstood my explanation but I have been unable to find something similar.

It is probably a bit late to rig up a sliding damper under the flue. The top of the flue is also a little high to easily reach (easily overcome, though). I could put a gal bucket I have laying around over the top of the flue when needed but this won't allow a lot of adjustment and will still lose heat. Even just a piece of fibro (which won't heat up as much).

Does anyone have any suggestions on how to approach the problem? Any help is appreciated.
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Old 07-14-2013, 02:10 PM
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Default Re: First time 41" clay/homebrew oven.

Gudday
What is the flue hieght from the hearth floor in comparison to the main dome height to hearth floor? If its near the 63 per cent a damper might be overkill?
Regards dave
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