Oven on wheels

[wotavidone]

Re: Oven on wheels

Nah, I've got plenty of other chores. Fixing kids cars, painting window frames. fixing kids laptops, aand drinking some of that cheap plonk.

[wotavidone]

Re: Oven on wheels

Awoke this morning regretting the cheap plonk somewhat, but shook off the cob-webs, and the worries about kids cars and laptops, and all the other stuff that mysteriously breaks down for them, but always seems perfectly fine in my hands (maybe a bit more careful with stuff?), and dragged my youngest out of bed to give me a hand.
He grizzled a bit, but we now have a slab of concrete hardening under plastic sheet. 4.5 inches thick with mesh in it. Forgot the plastic underneath!!
Ah well, it is laid on well drained sandy soil, none of the other concrete I've laid for garden paths has suffered due to lack of plastic, so she'll be right.
Bribed my boy by spending what I saved by getting my cement from the $6.95 a bag guy on his favorite KFC for lunch.

[cobblerdave]

Re: Oven on wheels

Gudday
Should have asked ages ago....whats the slab for?....is the oven on wheels to have a more perminent place?

Regards Dave

[wotavidone]

Re: Oven on wheels

The oven on wheels is going to lose its wheels and park up permanently.
I had a change of plan. I was much inspired by another Oz guy here on the forum who did pretty much exactly what I was planning. Steel frame, castors, build it in the shed, wheel it out when required. But he says it takes two guys to push it around, etc. And was so heavy he added a heap of castors. I have to buy them rather than "score" them so I decided to can that idea.
I welded the frame, and after I cast a scoriacrete floor in the tray, to build my oven on, I decided it would be too heavy to be truly portable. I decided on scoriacrete because it had a reasonable insulation value and a decent strength. (about 15-20 MPa). Look back a page or two and you'll see a pic. of what it looks like. The sand/cement paste surrounds the porous scoria without filling the air gaps, so the insulation value stays reasonable. I was looking at it tonight and I gave it a rap with my knuckles - sounds funny, sorta like you'd expect a suspended concrete slab to sound, but with a funny hollow ring to it. Could just be my imagination, I suppose.
I found this academic paper that had the analysis of scoriacrete. Strong enough so it actually has some tensile strength, which made it attractive to me, because the base of my tray is only roofing sheets, and it has a reasonable insulation value, even for the mix I used, which is pretty much a standard 3:2:1 mix, with the large aggregate replaced by the scoria. And you can mix it with an ordinary mixer.
So, after a bit of thinking, I laid a slab of ordinary concrete just off my carport, and that's where she's gunna stay. It has certain advantages. Of course, if I had decided on a permanent location initially, I'd have done a concrete block stand to start with. Ah well, it'll work out in the end, and I'm still coming in on budget.
I must photograph an oven that one of the local schools has done. Looks quite large, and rather dangerous. Its a steel frame, with a tray and a heap of red bricks laid on their side for a floor. Looks like an adobe dome. A real horno de barro, with no flue. Thing is, you can see where it sagged in the middle and they added a 5th post later. The legs are variously sitting on bricks and dirt, etc.
Very precarious, looking from outside the fence. I do not expect mine to sag, because I have a three inch slab of reinforced scoriacrete to spread the load, and I've already stacked all my materials on to check, but in anycase I have enough steel left that I will add the 5th leg before I build the oven. Start next weekend, assuming the wife's surgery goes OK this week.
I should add up the costs, but it might be better if I don't.

[wotavidone]

Re: Oven on wheels

Took a close look at the Bunnings oven kit yesterday. Interesting. They seem to simply sit the precast dome on a three inch reinforced concrete slab, then lay a thinish insulating blanket inside, with a layer of thin firebrick for a cooking surface. It appears to be ordinary concrete in the slab according to the literature. Insulation over the top of the dome, but pretty minmal underneath, it seems to me.
They had a smaller oven there that was ready to go, and had a remarkable resemblance to a FB Premavera 60, even the stand, though I am confident that if I was to stick my hand into an FB oven to feel the texture, I wouldn't knock loose refractory off the wall.

[cobblerdave]

Re: Oven on wheels

Gudday
Interested in your comment in the pizza stone section I paid a visit to bunnings on the way home tonight and check out the Ozito oven. Yep the inside surface of the dome was a bit dusty and soft... a finger nail would take a little off the surface. Give it a good rap with you knuckles it sound pretty firm. The instruction book in the oven recommended it still needed "curing burns" before using to full heat.
Perhaps the curing process would harden it a bit more but Gut feeling says No. Checked out the Allan Watt book which has a cast oven and that design has a paver skirt to protect the dome from the odd log and tool. So the cast type looks a little softer than brick.
Thats not all bad though just as long as you take proper care a cast oven should give you good service.
It was a little thinner in the hearth and the dome than say a forno oven but again thats not such a bad thing. I recon you could get a good pizza out of the oven anyway and being thinner wouldn't take as much heat/time to get to pizza temp. Lack of thermal mass would have an effect on slower cookin though....recon again if you owned the oven you would just adapt to it.
Important thing as always is that you just enjoy your WFO

Regards Dave

[wotavidone]

Re: Oven on wheels

Yes Dave that is one conclusion I have come to as well. Whatever oven you have you will adapt.
I was a bit taken aback, as the larger oven was as solid as a rock, and I assumed they were made from the same stuff.
The other thing that struck me, dunno if you noticed?, was that the domes themselves seem to sit straight on the concrete slab, with the insulation just under the fire brick floor.
The more I talk and read about WFO, the more I realise most people here on the forum are building the "Rolls Royce" of ovens, with their very thick insulation, their high thermal mass, 5 days of heat retention, etc.
Guys up here are telling me to use no insulation "as they get too hot".
I have insulated to a certain extent, with the scoriacrete slab, as it would be a bugger if you decided later that you needed it.
I'm toying with the idea of still putting an inch or two of vermicrete on top of that. Not doing anything at the moment. I took a weeks holiday, in case my wife needed me, but she's recovering well, and I could be doing a bit on the oven, if it wasn't raining.
I probably should have had a look around Adelaide for some insulation board to go on top of the slab, while I was down there for the wifes surgery this week, but its Clipsal 500 week, so traffic where we were was a bit chaotic, and I had other priorities. I was lucky to get to Bunnings.
On the plus side, I got a nice new laptop for $369
On the negative side, I was parked near the hospital, legally and I thought quite safely, I'd even taken note to make sure I wasn't doing a local resident out of somewhere to park his car.
Some bugger cut so close to my car they actually took the driver's side mirror of. Musta been awful close to taking out the entire side of the car. Then I woulda been stuck 130 miles from home, and 5 miles from the only hotel I could find with a vacancy. Did I mention it was Clipsal 500 week? At the pub they actually gave me the managers flat, as everything else they had was booked.
I recommend this pub actually. Dunno what the attitude on the forum is to mentioning businesses, but if anyone wants to know where they can stay in a very basic but clean hotel room with ensuite, between the airport and the city, for $80 a night for two people, with ample offstreet parking, about 2 km from the city centre, and 25% off meals in the restaurant for guests, and the food is very good, send me a PM.

[wotavidone]

Re: Oven on wheels

Currently running some test batches of homebrew mortar. One with purchased terracotta clay, one with my own white clay I harvested from the local wetlands and processed myself.
I know, I know, it aint fire clay.
However, while contemplating the FB homebrew mix the other day, it occured to me that it could possibly be thought of as adobe stabilised with lime and portland cement. So, given that fireclay's main claim to fame is that it can withstand temperatures much higher than can be found in a WFO, I decided to test ordinary clays.
I found a website the other day, which I must have saved wrong, coz I now can't find it in my favorites list. Anyway it was a pottery website that explained the cone scales, and it had a table of what temperatures the different clays had to be fired to to get them to change state/vitrify, whatever the term is. Anyway, fire clay would never even get close in a wood oven. (Neither would terracotta, it needs about 1000C).
So I thought I'd make a couple batches of homebrew mortar and test the following:
shrinkage, how easy it is to stick bricks together with either batch, what happens when you drop the hardened mortar, what happens if you put the hardened mortar in a flame, etc.
If it looks like a disaster, the local bloke now tells me he can get Calcium Aluminate cement for $42 per bag, so if necessary, I can get that.

[david s]

Re: Oven on wheels

I am inclined to agree with you re clay addition.i should think that almost any powdered clay will be ok. Fire clay in Australia is expensive.because it is not plentiful, unlike Europe and the US where fireclay is about the cheapest clay you'll find. Australian clays are high in iron which makes them unsuitable for high temp. When I say high I mean stone ware (over 1200 C). As we never get our ovens anywhere near these temps this requirement is irrelevant. As you have pointed out the shrinkage rate is more important and your tests will determine what is most suitable, although you should really test their shrinkage up to about 500 C Maybe you could take your test bars to a local potter. I think you will find there is not a great deal of difference, but would be interested in your results.

[wotavidone]

Re: Oven on wheels

My test slabs are looking good, with my "white" clay in front a bit, I think. A bit harder, a bit stronger, I reckon. I really must get this stuff assayed, definitely getting curious about the chemistry.
I had a look at the Littlehampton Brick Company website today. Their home brew mix is 1 Lime, 1 fireclay, 4 "foundry sand".
I have sort of been wondering about the cement - hardly seems any point to putting it in if it burns out.
Spent some time today drawing out the inner arch. I want to build it straight off my concrete slab, and run the floor bricks between the uprights.
Trouble is, I want to make it about 16 inches/400mm wide. Three bricks wide is 336 mm, a bit narrow, four bricks wide is 455mm, about 18 inches, which I feel is just a bit too wide for an oven of 750mm/ 29.5 inches.
Right now, I'm considering 3 bricks wide , with 4 wideish mortar joints of about 15mm each to fill the gaps. Only in the front "landing" bricks of course. Anyone have an opinion?

[cobblerdave]

Re: Oven on wheels

Gudday
Don't delete the portland ...its your initial "hold" so as it burns out the lime hardens and takes over as the glue for the structure.
I have a mate that has built an oven out west . Rammed earth and sleeper base(stablised with cement) house brick dome( yep the one with the holes) no hearth insulation, paver hearth, no entrance or chimney, dome insulation is chopped hay, clay, sand and cement. Hope to visit him some time to taste the ovens wares as I hav'nt seen him since his started.
Anyway he has used a version of the homebrew using unfired clay ....he recons to much clay leads to cracking so he has 1/2ed the clay and replaced it with extra lime. I'm sorry this is a bit of "here say" I hav'nt seem the oven myself so I can only go on what I'm told....but unfired clay would have a tendancy to crack when the moisture dried out unlike fired clay which would not soak up moisture. Worth a tought I recon
Hearth insulation...well that oven has none...figure? If you would like more insulation consider Hebel. My own oven has survive 18 odd months with Hebel insulation under the heath bricks...still strait and true. Its cheap easy to use cheap and your local bunnings stock it for sure.

Regards Dave

[wotavidone]

Re: Oven on wheels

G'day Dave, its interesting isn't it?.
My test piece made with my own clay is showing no sign of cracking as it dries out. Starting to think it aint clay! Except when I fire it to a nice dull red heat, it goes hard, water proof and a nice terracotta colour. Definitely having it assayed. Actually, I think the trick is to keep it moist long enough for the portland cement to develop some strength, so the clay can't pull it apart.
I'm thinking the clay that goes in the mortar should definitely be unfired. Otherwise its just another aggregate. Whereas unfired has some part to play as a binder.
Sounds like your mate has made a real horno de barro! Bet the tucker that comes out of it is fantastic.
With regard to deleting some of the clay and adding extra lime, the blokes up here who already have brick ovens say they just used ordinary brickies mortar with half the cement replaced by lime. Looks like just about anything works as long as you don't rely on the portland cement for long term glue.

[david s]

Re: Oven on wheels

[QUOTE
Trouble is, I want to make it about 16 inches/400mm wide. Three bricks wide is 336 mm, a bit narrow, four bricks wide is 455mm, about 18 inches, which I feel is just a bit too wide for an oven of 750mm/ 29.5 inches.
Right now, I'm considering 3 bricks wide , with 4 wideish mortar joints of about 15mm each to fill the gaps. Only in the front "landing" bricks of course. Anyone have an opinion?[/QUOTE]

I'd be cutting the floor bricks to fit the space designed. It is better to butt the floor bricks together rather than mortar them. Lots of builders have preferred to lay the floor in a herringbone pattern to reduce the tendency to catch the peel. This would necessitate cutting the bricks anyway.

[wotavidone]

Re: Oven on wheels

I'm haven't even thought about the pattern to lay the floor bricks yet. I was going to do my walls straight down to the insulated slab, then fit the brixks inside. I am using pavers, which have the advantage of a bevelled edge for minimising catching the peel, but the bricks in question are the ones under the arch, right at the front, which I thought would simply go in straight. I'm just to about to go out and fit a masonry blade to my drop saw and see if they cut reasonably easily, because ideally I'd go 3.5 wide with no mortar. Decisions, decisions, I don't like 'em, and generally avoid them.
You are probably right - design the arch, build it, then fit the floor bricks in. Definitely means better progress.

[wotavidone]

Re: Oven on wheels

P.S. part of the plan was to simply drop the bricks in loose, not even bedded in anything if they fit ok, with the view to being able to pull them out and substitute 30mm firebricks and 25mm insulation later if I deemed it necessary. So I was going to build an arch, circular first course, bed the front four bricks in under the arch, then start laying the floor bricks in the contained area created.
Or is this a difficult way to do it - apart from a lot of cutting of course.