New Build in South Oz

[wotavidone]

Re: New Build in South Oz

Gudday mick
WOW
Oven building by committee .... Now that's a concept I had never considered?
Must be interesting.... Keeping a bunch on track ... With beer involved... Southward is not a iffy beer either
Regards Dave

The committee is well stocked with men who run their own one and two man contracting shows. No output, no pay, so these guys like to make a decision and get on with it.
Very Interesting.
Southwark is right up there with vegemite.
If you were raised on it, you like it. Otherwise it's "How on earth can you stand that crap?"

Never gets a good review, unless it's a South Aussie writing it.
Southwark Bitter

Funny thing is, lots of reviewers say its a substitute for VB, whereas most guys I know won't touch VB.

[wotavidone]

Re: New Build in South Oz

Got most of it done today.
No beer and supplies run interfering today.
Did a full ring and 4 out of the 11 bricks we estimate we need in the final ring.
Turns out the film She Who Must be Obeyed wants to see (requires a 110 mile round trip to go to the cinema in Port Augusta) is not on til Tuesday. So we are allowed to finish the dome tomorrow.
7 or 8 bricks in the final course, and a keystone.
8 days to build the dome.
We gotta get it done. She Who Must Be Obeyed fired up this morning, about all his unfinished projects.

By lunch time all was forgiven and SWMBO made us chicken curry and rice for lunch.

[oasiscdm]

Re: New Build in South Oz

Looks likme the committee approach works .

But the oven will be unfinished if you start the cooking process prior to final render if that what you are doing. Seems most stop the build once they can fire oven up and cook.

[wotavidone]

Re: New Build in South Oz

Looks likme the committee approach works .

But the oven will be unfinished if you start the cooking process prior to final render if that what you are doing. Seems most stop the build once they can fire oven up and cook.

So true. I've been telling the committee that there is a way to go from here.
We got the keystone(s) in this afternoon and sat down to have a stubby and discuss the next steps. I've been telling my mate that the next step I'd like to do is coat the outside of the completed dome with a layer of lime rich reinforced render to beef up the thermal mass and tie everything together.
The whole committee can't see the need, because, not having been fired to 4-500 C, this thing is currently as solid as a rock.
Of course, I'm saying that it will be subjected to tremendous stresses, and any help we can give it, we should.
He plans to build the enclosure from hebel block, so the whole house is one big block of insulation.
Next step is to build the front entry/smoke chamber/chimney.
That is going to be an adventure.
My mate would very much like to see the chimney run back over the dome and rise from the centre of the oven, a la Neapolitan pizza ovens.
I've been trying to figure how we would do that, since the ones I have seen have a brick lined channel.
The thing is, that isn't really insulated, which doesn't matter for a Neapolitan pizza oven, but surely must for a retained heat baking oven?
He can't see why the channel up over the dome can't be made from Hebel, but, despite my faith in the stuff, it is reasonably fragile compared to brick and I have my doubts about long term direct exposure to combustion gases.
More decisions.

[oasiscdm]

Re: New Build in South Oz

Tell them I said it [Hebel] cracks if in direct contact with heat. It insulates very well my hearth under full firing does not get above 48c at its base. I am using a scrap piece of hebel panel [ which is reinforced whereas block isn't ]for a temp door and it has cracked severely,

Not sure I get it, he wont add extra thermal mass has, thin walls any way, but wants to run the flue back up to the middle of the dome from the landing. That adds nothing to the oven in any way but provides an indirect path for flue gases to travel. Hmmmmmm interesting....

Is he going to use blanket around the dome?

You can get flexible flue that will follow the path of the landing to the dome I believe have seen it in my own research

[wotavidone]

Re: New Build in South Oz

Colin,
Do your floor bricks lay straight on the hebel like Cobblerdaves?
I think the layer of bricks protect the hebel from the direct fire, and ensure the hebel heats slowly and evenly.
With all respect to my mate, I do hope to win the debate about the thermal mass/reinforcement. An inch of render will result in 4 inches of thermal mass. According to the Forno Bravo plans that's "high but acceptable" for a domestic oven.
I also will try to convince him on taking the chimney straight up from the entry.
The plan with the rest of the insulation is to make the enclosure from the rest of the hebel blocks he has, then pour perlite into the voids. Rectangular "house", round oven, gotta be some voids, right?

Perlite, because there just might be a supplier here in town.
Right now, I'm expecting we will end up with an oven with 3 inch floor, 4 inch dome, and very well insulated. My hope is this will allow reasonable heat up times and good ability to roast meats in the oven.

[wotavidone]

Re: New Build in South Oz

Photos. First flame.
Having trouble loading photos

[UtahBeehiver]

Re: New Build in South Oz

nice brick work closing the dome tight and symetrical.

[wotavidone]

Re: New Build in South Oz

nice brick work closing the dome tight and symetrical.

Thanks Russell. I do subscribe to the theory that the tighter the bricks fit the less critical the mortar is.
Speaking of management by committee, there was a couple of strong opinions on how the last brick should be cut. Two guys competed to make the keystone.
One by cutting bricks with an angle grinder, one by boring a brick with his concrete borer.
The winner was the angle grinder, the other guy isn't happy with me for not using his perfectly round plug. Unfortunately it was about 20mm too small in diameter.

[oasiscdm]

Re: New Build in South Oz

Colin,
Do your floor bricks lay straight on the hebel like Cobblerdaves?
I think the layer of bricks protect the hebel from the direct fire, and ensure the hebel heats slowly and evenly.
With all respect to my mate, I do hope to win the debate about the thermal mass/reinforcement.

No bricks sit on calsil board 2" thick then hebel.

[wotavidone]

Re: New Build in South Oz

Progress report.
Managed to score some 65 mm pavers. These were just what we needed to get around a particular issue.
i.e. with the three inch/75mm bricks sitting on the floor, we had an issue with mortaring the floor bricks under the outer entry. We wanted to do this to retain the floor bricks inside the oven in place, but then the mortared bricks would be higher than the floor bricks. With the 65 mm bricks there was room for a 10 mm mortar layer. So there is now an apron of bricks in front of the oven.

Next problem:
The client who, as supplier of the materials and beer, is always right, wants a rectangular entry, one and a half bricks deep, with a flat top. i.e. not even a shallow arch to stop the roof bricks falling in.

Hmmm. Steel lintels, maybe?

He didn't like the look of that, , and I figured there would be all sorts of movement cracking everything.

However, three Southwark stubbies later, new idea.
We will obtain some house bricks, the ones with the holes through them. We will fabricate the roof of the outer arch in one piece, consisting of bricks mortared together with reo rod running through the holes. Sort of hidden lintels. I reckon, with the reo inside the bricks , it can't get hot quicker than the bricks, so the expansion rates get closer together.

Taper everything to a 7 inch by 7 inch chimney hole in the middle.

Why 7 inches by 7 inches? Because we have discovered that all the old fire extinguishers he has are not aluminium as first thought, but some sort of non-magnetic steel, presumably stainless.

So, we will be having a flue fabricated from 7 inch diameter stainless steel that is about 2 mm thick. Beautiful.

Remember the committee of self employed contractors supervising this job?
It would appear one of them knows a man who has welding equipment capabilities the home handyman can only dream of.

My only concern is whether we can shape everything for good air flow.
Like everything else we've done, we'll cut some bricks and try a few things.

I reckon the old drop saw I bought at a garage sale is going to be fit for scrap by the time we finish. The bearings are getting noisy and it tends to run off course a bit. Still 2 ovens for a $25 investment is pretty good.
When we've finished I'll pull it apart and see if the bearings are replaceable.

[wotavidone]

Re: New Build in South Oz

I've found a list of expansion coefficients that says steel expands at around 16 x 10-6 metres per metre per K.
At least, that's what I think it says.
Anyway, if I work this out right, increasing the temperature by 400C gives a 6.4 mm increase in length per 1 metre length of steel.
Anyone reckon that sounds about right?
I'm thinking that expansion over about 600mm is not going to be an issue, since I sincerely doubt the bricks of the outer entry tunnel are going to get anywhere near 400C.

[david s]

Re: New Build in South Oz

I think the main problem of steel reinforcing in the refractory is the greater thermal conductivity of the steel compared to the refractory. It means the heat rushes to it and expands it more than the refractory that surrounds it. I think this is why stainless needles are used. Stainless so they won't corrode as easily in the hot and moist environment and needles so they can dissipate their heat more easily to the refractory that surrounds them. Steel and concrete in the normal situation have almost identical expansion rates and that's why they are so good for reinforced concrete in bridges and buildings etc, but any heat increase from the weather is slow enough for both materials to equalize their temperature and therefore their expansion easily, not so when heating an oven at 400C/hr. Also presuming brick, or castable have similar expansion rates to concrete.

[wotavidone]

Re: New Build in South Oz

I think the main problem of steel reinforcing in the refractory is the greater thermal conductivity of the steel compared to the refractory. It means the heat rushes to it and expands it more than the refractory that surrounds it.

The steel will be encased in the brick. If the brick has a lower conductivity than the steel, how will the heat rush to it?

BTW, many stainless steels have a higher thermal expansion and the same thermal conductivity.

http://www.engineeringtoolbox.com/li...ents-d_95.html
http://www.engineeringtoolbox.com/th...als-d_858.html

It really depends on what steels you are comparing, but I reckon the only real reason to use stainless is the corrosion resistance, if you need it.

[cobblerdave]

Re: New Build in South Oz

Gudday Mick



Outer arch added later. But flat brick entrance supported by angle iron. No cracks as this is possible cooler than the entrance. Oven entrance is also angle iron and also supports the rear wall of the chimney which is 5 bricks high. This has 2 cracks which cannot be photographed cold probably due to the soot if anything. Hot they can be seen a mm or two wide. They don't appear at the top of the chimney or outside. It think I expected a least some cracking. So they don't bother me and I don't bother them.
Regards dave