mrjl
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Post by mrjl on May 21, 2018 7:54:59 GMT
Hi, Oven newbie here. I'm using a steel barrel to form my barrel oven. It's cut and in place. I'm using old storage heater bricks for the oven floor. I've got all of the materials for fire proof concrete on their way to me. Before I commit I wanted to ask if it's ok to use the concrete blocks as pictured in my photo? They're not fixed yet, just placed on the slab. There's a gap between the barrel and the blocks although that's not visible in the photo where the blocks are tight to the barrel, they'll be flush with the edge of the slab when I fix them, so about an inch or so outboard of where they are in the photo. That gap will be filled with the perlite based fire concrete I'm going to make. Then the concrete will go over the top of the oven, followed by ceramic insulation from Victas and then finally render over the lot. I could use the perlite concrete in place of the blocks but I had the blocks spare and thought it would be a good use for them and would save on the amount of concrete I'd need to use around the barrel and also get around the trickier issue of surrounding the barrel with concrete without it all slopping off (this is the first thing I've ever built so I'm no expert). Will they be ok or will they crack and ruin everything? I'm creating wooden form work for the mouth of the oven which will hold a 150mm chimney (with damper, on its way from eBay too). If there's anything else that's a glaring mistake or better suggestions on how to do any aspect I'm all ears! Cheers  |
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Post by downunderdave on May 21, 2018 8:33:48 GMT
If you are planning on using the drum as a mould and then removing it you will have a lot of trouble unless you place wedges under it so it can drop to remove. If you plan on leaving it in place then you may find that because the steel is so much more conductive than brick or mortar, it will expand and probably crack your brick/mortar layer over it. In addition the heat will accelerate corrosion so in 5 years time you may end up with rusty flakes on your pizzas.
Regarding the concrete blocks, they’d be far better replaced with clay bricks as concrete blocks don’t like anything north of 300C.
Also it appears that you have not insulated under the oven floor which is mandatory if you want to achieve and maintain decent cooking temperatures.
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mrjl
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Post by mrjl on May 21, 2018 8:44:17 GMT
If you are planning on using the drum as a mould and then removing it you will have a lot of trouble unless you place wedges under it so it can drop to remove. If you plan on leaving it in place then you may find that because the steel is so much more conductive than brick or mortar, it will expand and probably crack your brick/mortar layer over it. In addition the heat will accelerate corrosion so in 5 years time you may end up with rusty flakes on your pizzas. Regarding the concrete blocks, they’d be far better replaced with clay bricks as concrete blocks don’t like anything north of 300C. Also it appears that you have not insulated under the oven floor which is mandatory if you want to achieve and maintain decent cooking temperatures. Thanks for your input. I had planned to leave the drum in place. I doubt I'll still be living in this house in 5 years so it's just a first go/practice oven really. I've seen a few of these built before and the cracking didn't seem to be an issue. The steel is only 1mm thick for 99% of the drum. Perhaps I should look in to making it removable though. What do you recommend to insulate under the oven floor? Ceramic insulation too or some kind of board? |
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Post by simonh on May 21, 2018 9:03:32 GMT
The thing to remember with WFO's is that you are building a heat store, it is that stored heat that you are cooking with not the open flame. The more heat you are able to store and retain the more you have available to cook with. The best way to achieve this is with lots of insulation and the use of material that hold and release heat in a linear way. If you do a good job of this then you will use less wood, and won't need to keep pulling coals over the floor between Pizza's to put heat back in.
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mrjl
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Post by mrjl on May 21, 2018 10:14:56 GMT
OK thanks guys, I think perhaps I'll swap out the blocks for perlite concrete so that it'll store more heat. What should I use as insulation under the fire bricks though?
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Post by oblertone on May 21, 2018 12:43:48 GMT
I used a sheet of 25mm vermiculite board under storage heater blocks; available from eBay or your local stove installer.
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mrjl
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Post by mrjl on May 21, 2018 13:08:40 GMT
I used a sheet of 25mm vermiculite board under storage heater blocks; available from eBay or your local stove installer. Thanks. Does your oven cook pizzas no worries? Or do you need to keep topping the fire up? |
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mrjl
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Post by mrjl on May 21, 2018 13:11:00 GMT
I should also add that under my heater bricks there is a 60mm steel reinforced concrete slab. Will this not insulate it at all?
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Post by crammy on May 21, 2018 14:11:07 GMT
Hi. The insulation is to stop the heat being absorbed by the concrete slab. you want as much heat to stay on the hearth. without the insulation you fire would bea heating up the concrete too and consequently loosing heat from the oven
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mrjl
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Posts: 42
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Post by mrjl on May 21, 2018 14:15:34 GMT
Hi. The insulation is to stop the heat being absorbed by the concrete slab. you want as much heat to stay on the hearth. without the insulation you fire would bea heating up the concrete too and consequently loosing heat from the oven Makes sense! Thanks |
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Post by crammy on May 21, 2018 14:49:44 GMT
No problem
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Post by oblertone on May 21, 2018 16:58:23 GMT
As above, the heater blocks store heat (strangely), the insulation is to stop the heat going elsewhere, you really don't want to be heating up a big lump of concrete.
My oven will cook pizza all night long, the most I have done in an evening is 70, yes you will need to keep feeding it but a stock of sticks no thicker than your wrist will keep it at cooking temperature for as long as you want.
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mrjl
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Posts: 42
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Post by mrjl on May 21, 2018 17:53:28 GMT
OK so I'll definitely buy a vermiculite board for underneath. I'll also lose the blocks around the dome and just use perlite concrete instead.
Still unsure about leaving the barrel in though. I might look into cutting it up and reassembling it around a wooden skeleton that I can disassemble or burn out once the oven is ready. It's so thin I can't imagine it expanding that much, but I'm not an expert. A friend did his oven around an old cement mixer barrel and hasn't had any cracking.
I'm also looking for a bit of advice on the best ratio/mix for the concrete. I've ordered perlite, ciment fondue, grog and plasticiser from a supplier but they're yet to get back to me with details of the mix. Does anyone have a link to a reliable recipe?
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Post by oblertone on May 22, 2018 7:48:57 GMT
The most common and recommended mortar mix is known as 'homebrew' and while there are variations the normal mix is sand-cement-clay-lime in the ratio 3-1-1-1 by volume. Highly recommended, easy to work and inexpensive.
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mrjl
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Posts: 42
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Post by mrjl on May 22, 2018 10:27:18 GMT
The most common and recommended mortar mix is known as 'homebrew' and while there are variations the normal mix is sand-cement-clay-lime in the ratio 3-1-1-1 by volume. Highly recommended, easy to work and inexpensive. Hi, Thanks for the info. That's for a mortar mix though. I'm talking about making a perlite concrete mix that would surround the dome in place of fire bricks, rather than a mortar that would stick bricks in place. Does that make sense? These are the guys I've bought my supplies from, if you look halfway down the page under 'Option 1' it has ovens with a concrete dome made out of a perlite/ciment fondue/grog mix: www.pizzaovensupplies.co.uk/outdoor-pizza-ovens/ |
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