40" brick oven on Tasman Peninsula

[Blunt Tool]

Hi All,

I confess I've been lurking around this forum for a while now, and have learned a heap from all the information available. I'm now well into a 40" brick WFO of my own, and have decided to post some pictures of the progress. I'm generally not one to advertise and wasn't going to display my progress, as to be honest I find it hard to believe anyone might be interested, and that may well still be the case! But I've changed my mind about posting mainly because I have changed plans mid-way through, and as a result may not have done things the usual way. If anyone else can learn from what I've done, or haven't done, or should've done, then that will be great. It will add to the pool of information around the place here and be my way of saying thank you for all that I've learned so far, and no doubt am still to learn!

So here goes?.
Any comments, criticisms or suggestions gratefully received.

Andrew

[Blunt Tool]

Re: 40" brick oven on Tasman Peninsula

The project started July 2013. We had an external contractor do the paving and the base slab due to time constraints.
We did the gabion walls ourselves (mostly my wife).

[Blunt Tool]

40" brick oven on Tasman Peninsula

My uncle helped me with the block work for the base. We didn't actually check that the slab was level first, and it turned out it wasn't! By the time we realised the clockwork was about 20mm out side to side, which we couldn't really correct for at that stage.

[Blunt Tool]

40" brick oven on Tasman Peninsula

At this point I was effectively following the plans for an oven that a mate had built. Not knowing a great deal about it all, I noticed his worked well and thought I would do the same. Turns out it is more of a barrel vault type brick (bread?) oven.

These plans called for a vermiculite / cement insulating slab, underneath a suspended concrete slab. The formwork for the concrete slab had rebar running through it, and sat on top of the blockwork base. By angle grinding out some recesses into the blockwork to take the rebar, I could correct for the slope on the slab and hopefully get it all level again.

The vermiculite layer in theory was supposed to be supported by the underside of the concrete slab, but I was a bit sceptical about it as I wasn't sure how much weight would be in it. I drilled a few side holes into the blockwork and put a few short pieces of rebar through to give it some lateral strength. I also added a few large screws sticking up out of the vermiculite layer to help it join to the concrete slab, as I poured them a day apart. When I poured the concrete slab I also core filled the clockwork base.

[Blunt Tool]

Re: 40" brick oven on Tasman Peninsula

At about this point I discovered Forno Bravo!

I decided that a pompeii style oven would be better for our needs, as this is being built at our holiday house and I won't always have (or want to spend) 4 hrs firing it up like my mate does before we eat pizzas after a day at the beach. After measuring the slab I thought a 40" oven could just fit?

I put the base down a couple of days after Christmas, put in a plywood form I had cut and did the soldier course around that.

The Indispensible Tool I am using is about my third attempt at creating one, after finding out the hard way you can't substitute for a lack of welding skills with a tube of superglue! It works well, although I gave up clamping the bricks to it pretty early on as it was causing more trouble than it was worth (not 100% square to the centre, and a rusty clamp that would dislodge the brick every time I tried to release it!).

[Blunt Tool]

40" brick oven on Tasman Peninsula

Things have been progressing slowly but well since then. Like most I've found it to be a pretty steep learning curve! Bricking up around the entrance arch has been tricky but I think I did ok there and am glad to be clear of it now. Also got better at my cuts but the gaps between the bricks have been pretty variable.

We are planning to enclose it completely at the finish, with a whole heap of bricks we have left over from paving that area last year, so I haven't been too concerned about how it looks on the outside.

As it is our holiday house, apart from a few days between Christmas and New Year I haven't really had any time to work on this except for weekends. That is no drama but it has meant I haven't been able to keep the bricks and mortar as wet as I would have liked between efforts. I'm hoping I won't pay for this too much with some big cracks when it comes time for curing!

[david s]

Re: 40" brick oven on Tasman Peninsula

It looks like you were starting with a Scott oven which has a massive amount of thermal mass. As you have now converted to a Pompeii oven you should have placed insulation between the floor bricks and the supporting slab. Check the Pompeii plans. The way you have it presently arranged means it will be like your mates and take 4 hrs to heat up. As a rough guide it takes the heat about 1 hr/ inch to move through the bricks and the same for the concrete. Perhaps it's not too late to include insulation under the floor rather than under the supporting slab.Then again maybe it is, I hope you have access to a good free wood supply.

[Blunt Tool]

40" brick oven on Tasman Peninsula

And finally last weekends effort?.

[Blunt Tool]

Re: 40" brick oven on Tasman Peninsula

Next row I think I will move to 1/3 bricks as gravity is really starting to have an influence! I'm guessing I have probably another 3 rows to go before the cap. Hopefully I can get the dome closed this weekend (long weekend here).

I'm starting to think about the next stages beyond that. The entry and flue I think I have under control, but I'm undecided what to do with regards insulation, and whether or not I need more thermal mass? Presently I'm thinking of coating the whole thing with an inch or two or mortar first, as this might give the whole thing a bit of a seal to prevent heat escaping through those cracks I'm worried I might have (because i haven't been able to keep it wet enough). After that I was planning on another few inches of concrete for thermal mass, before lots of insulation. Now though, in view of the fact I have a large concrete slab directly under the hearth bricks, perhaps I already have enough thermal mass? Ideally I would like the oven to stay hot enough to cook bread for 24hrs or so, but I don't want to spend half a day heating it up before I can cook pizza either. I know this is the million dollar question, but where is the compromise?

Admittedly I haven't started working my way through the forum yet for information, but does anyone have any thoughts on this?

Andrew

[Blunt Tool]

Re: 40" brick oven on Tasman Peninsula

It looks like you were starting with a Scott oven which has a massive amount of thermal mass. As you have now converted to a Pompeii oven you should have placed insulation between the floor bricks and the supporting slab. Check the Pompeii plans. The way you have it presently arranged means it will be like your mates and take 4 hrs to heat up. As a rough guide it takes the heat about 1 hr/ inch to move through the bricks and the same for the concrete. Perhaps it's not too late to include insulation under the floor rather than under the supporting slab.Then again maybe it is, I hope you have access to a good free wood supply.

Thanks David. I didn't see your post there.

Unfortunately I changed plans after the slab was poured so can't do much about that now. I guess I can limit any more thermal mass I put in from here, and go overboard with the insulation? At least wood is something I'm not short of around here!

[stonecutter]

Re: 40" brick oven on Tasman Peninsula

If you didn't mortar the hearth brick, you could pull up the majority of them. From there, you could add 2" of insulation, then use splits, since your brick are orientated as rowlocks. At least then you will have a more balanced oven.

[Blunt Tool]

Re: 40" brick oven on Tasman Peninsula

If you didn't mortar the hearth brick, you could pull up the majority of them. From there, you could add 2" of insulation, then use splits, since your brick are orientated as rowlocks. At least then you will have a more balanced oven.

The hearth bricks aren't mortared in, just held with a thin layer of sand / fireclay. Putting insulation in underneath will raise them to around the top of the soldier course and drop the height of the dome by 2". Neither a big deal really.

Can I ask what you meant by a more balanced oven? If all the thermal mass (relatively) is under the hearth, and only insulation over the outside of the dome, will this affect the performance of the oven other than taking longer to heat up?

At present my choice seems to be between the time/hassle spent frigging around with the hearth bricks now, v's more time spent firing it up each time. Or is there more to it?

Andrew

[cobblerdave]

Re: 40" brick oven on Tasman Peninsula

Gudday Andrew
A pretty standard forno type oven has a 50 mm split tile floor And a 100 mm dome shell insulated top and bottom. As Davids has pointed out it takes an hour roughly for the heat to penetrate 25 mm of mass. Heat goes up so the dome heats faster but you can generally say that in two hours of brisk fire in a forno oven the heat has arrived at the insulation layers. The oven is now at saturation point. Maintain an active fire in the corner and that will supply enough heat the replenish the oven as you cook pizza at 450 to 500C over any number of hours.
Close that oven off with an insulated door and its possible to cook in the retained heat over a weekend. This is what makes the forno oven a great weekender and all round oven.
In your current configuration you have a floor of brick set on 115 mm side with another 100 mm of concrete before your insulation. That's 200 mm of floor mass. I'll let you of the math. The mass of the floor is not balance with the size of the oven. You would be hard pressed to get enough fire to heat it much less maintain pizza heat. The mass of your floor is more suited to a much larger oven
You did invite comment, but still I am truly sorry to be so blunt.
You can still change things now. Floor brick set on the 70 mm side on a 100 mm of pearlite cement. I know you are fairly advanced but the experience you have gained would make a rebuild so much faster and easy.
Regards dave

[NCMan]

Re: 40" brick oven on Tasman Peninsula

I'm no expert, but is it also possible to just add a layer of firebrick or even a layer of splits to what is already in place? I'm just trying to look at it as yet another choice. I realize nothing can make it as good as tearing it down and starting over, the right way, but weighing all possible "compromises" is a good idea.

[stonecutter]

Re: 40" brick oven on Tasman Peninsula

Nothing need to be torn down.

His floor brick can easily be removed ( the ones not supporting the dome) insulation can be installed, then splits on top of the insulation. Laying splits on top of the existing floor only creates more mass, and adds no value. Because the floor brick are oriented as a rowlock, he should have 4-4.5" between the slab and the top of the existing floor.... Assuming he has standard 9"x4.5"x2.5" firebrick. Splits are 1.25" thick.

Take out what you can, insulate, then lay the splits level with the remaining brick that couldn't be removed... Which will be most perimeter brick, not the cooking surface, where you don't want a bunch of heat sucking mass.