Clay Oven Plinth Support

I think I'd just build a plywood form, lay some evenly spaced 1/2" cast iron pipe lengthwise, (making sure it overlaps the breeze blocks), and pour concrete in it.

The pipe is cheap and will handle the load of the oven, and the slab will give you a nice base for the oven.

Thanks for this, I hadn't considered this method. Are you suggesting using cast iron drain pipes?

I had a look at prices round here (Just outside London) and it was very expensive for cast iron drain pipes, much more than lintels, but perhaps with some investigation I could get them from a scrap yard.

I haven't been able to find any scrap yards like you see on scrap heap/yard challenge. Round here the scrap yards are small, metal comes in and it is gone within a couple of days. I guess because land is at a premium, but I can keep on looking.

Sure. I was thinking along the lines of scrap pipe, but anything sturdy would work.

If any concrete structures are being demo'd around you, you might be able to grab some thick rebar.

those forms have to be strong.

Found a good set of plans with valuable tips...
http://myoutdoorplans.com/pizza-oven/outdoor-pizza-oven-plans-2/

Thanks, I like these plans. This is what I am considering. The picture shows 6" high concrete which is great, they don't mention any details about the mesh though. Just from looking at the pictures the mesh looks like it is spaced a lot less than the 20cm (9") that I was considering.

So I found this mesh which is spaced at 1"

1" x 1" x 10 swg mild steel weld mesh

http://www.metals4u.co.uk/mild-steel/weld-mesh/1-x-1-x-10-swg/detail.asp?prd_id=2519

This seems the cheapest and best option so far.

I'm still kind of winging it on the calculations though.

The paving slabs, atleast the ones I used, have a foam core.

I haven't seen those before. Here just outside London the hardware stores stock mainly concrete slabs. You have to be really careful moving them though. Just moving some I had from the front of the garden to the back I broke three in half!

Also I Iit a very small fire on one to keep the mosquito's away while I was digging up the clay and the thing cracked apart in 4 places.

I don't have a lot of confidence in them due to their brittle nature. They seem fine if fully supported by the ground though.

Read my email re heat and concrete,the two don't get along well and you will have problems if you try to light fires on concrete

My stepson built exactly the same thing you are trying to build and it is on a thick concrete slab on top of a base similar to yours and with a completely domed top much like an igloo and he used brick on top of his slab and then built a domed former and covered it with brick I am not sure if he used fire brick or just clay brick and then covered the whole lot with concrete and the top has cracked after a few years of use but it did at one time have a very big fire lit in it by one of his sons on a cold night

The bakehouse oven in the town where I lived as a child was all made of clay brick and very thick it was too and it was wood fired off a separate side firebox

Cheers

Peugeot man

Thank you for the advice. It is always good to hear from another persons experience.

I don't see any way to build the structure I want without concrete\steel unless I built a complete clay\brick arch for the wood store and then put the plinth on top of that. But it's a bit too late for that.

My plan is to ensure it is completely insulated at the base. The general plans for the dome are three layers 7cm (3") each, 1st layer clay\sand, 2nd layer insulation, 3rd layer clay\sand.

For the base I plan to put a fire cement\insulation layer that is double this thickness, and then do the layers above, so I'm pretty sure no heat will get through. I may even purchase some fire board, I haven't decided yet, but I will make sure it is properly insulated.

And the only away I found out that the paving steps were foam core, was I bought a pallet load of pavers, and as I was using them, (2) were defective because the foam had broke the surface. And the foam looked like the expandable stuff you would buy in a can.

But there are silo blocks also. They are pretty heavy any where from 50 to 85 lbs each.When it has to contend with heat, I don't think concrete is the best, unless you use fire brick on the inside. but these would have other problems where how you attach them, and also, they cant get wet, they are so porous, they absorb water, and may 'explode' when heated due to the water turning into steam. (unless your do it slowly.

I'm getting off your intend and just putting this out there but there may are other alternatives, I have designed incinerators/catalyzers , where the inside is heat resistant batting, and then you spray on a heat resistant coating to firm them up.

Another was a tunnel pizza oven (72" wide by 100 feet long) the insulation was 8# mineral wool. structure was stainless and aluminized steel. And as kram mentioned to make a form, but you can use a ceramic mix then is denser and heat resistant (anywhere from 1000-1500+ degrees F) . We did this for the fire tubes on the pizza oven. but those forms have to be strong.

That tunnel pizza oven sounds like such a fun project. I remember seeing one on How It's Made.

I do plan to insulate above the cement line so there shouldn't be any issue. The ceramic mix is interesting, what was that made up of? I do need heat storage at the base. I was planning red clay bricks and sand, mainly because my garden seems to be full of them.

Also it will have a roof as otherwise the clay would wash away, so there shouldn't be any rain water.

I don't recall off hand, I had obtained a premix, but I did google it.

Here they have premixes as well as enough recipes information where you can mix your own along with what stated from other posts.

I didn't catch what you were going to use this for?

When we casted our fire tubes, I always found that you had to get the feel of the cement, because if you followed the directions, at times it is too dry a mix. But when you add water, you have to extend the curing time. so that it will dry out.

One other thing to, is look at precast chimney flue liners..... they are lower temperatures, may work if you have an impingement plate.... (piece of sheet metal)

In our area a distributor had various sizes and shapes.

my hyper links didn't come through.

this is when I googled it

and

refractory mortar formulas

You will need to cover any concrete surface with clay brick or the heat will spall off pieces of the concrete and eventually ruin the concrete slab

Cheers

Peugeot man

I understand this and I have plans to let no heat through to the concrete at all. I just hope they work.

For a clay oven this is far more important than a pizza oven. With a pizza oven you keep the fire going constantly while you cook, so insulation doesn't matter so much. But with a clay oven you put the fire out and can cook your food from the heat stored in the clay for almost 24 hours. So obviously insulation is very important! My plan is for no heat to reach the plinth, it all depends on how well I do the insulation layer. I plan to double the thickness of this on the base to be sure.

All the above sounds like overkill to me, it's an oven not a skyscraper (I reserve my constitutional right to being wrong)

I'd have thought wood will work fine if it's having brick/clay over it.

A couple of railway sleepers or big fence post should do it, no prob'.

Oak is good...

Del

Now you're giving me ideas, modular formed skyscraper pizza ovens...

I too have thought am I just over thinking this! I have a railway sleeper in the garden spare and I also have some wood which looks like roof rafters size.

I have a couple of worries. I don't want it to bend over time and crack the oven. I also don't want it to be too large. Those railway sleeps are huge and space is actually at a premium. I want the oven to be about waist height, but it also needs good heat storage and insulation in the base. So that's a few layers of bricks and insulation. Normally you'd build these clay ovens with no gap underneath so all the heat is stored below.

I think it'd probably be fine like you said, I just have a bad feeling about it.

Have a bad feeling too about the creosote that will ooze out of it when the sleeper gets 'king 'ot!

I meant an untreated one or some timber that size...

But guys, get a grip, it's going to have clay, brick, sand all sorts of stuff on top of it... for pities sake they built houses and warships out of wood and had fires in both... staircases were often made of Oak because it wouldn't catch fire easily.
You're not going to try to cook pizza on a hot log.

Any how I think the OP mentioned a wood store underneath, and that's not going to catch fire. Cheezes this thing can't weigh that much.... I despise overdesign.

And btw, I've seen steel bows, even a pre-stressed concrete one.

I'm going to hide in my secret cat nest before you start inserting piling to take the load of this oven... prob' be getting planning permission for it too.

Despite my protestations I'm open to offers of pizza and beer

Del

frankly Del, I thought we were just kicking ideas around. Some of the references used was over kill and was not to be taken literally, but unfortunately,... was.

Yes, one has to lighten up..... Just a sec... is that tuna I smell.?

OK I'm going to have a think about your plan. I have spare in the garden 1 concrete fence post and at least 5 wooden fence posts. I could use the concrete fence post as a mid support for the fence posts to lay on to stop them sagging. I also have some thick plywood I could lay on top of the fence posts if needed. I'll measure up over the weekend and see if I can come up with a plan.

I don't think even a single 4" square fence post supported across 1250mm is going to sag much*, never mind a row of 5. That's probably better support than the average upper storey of a house (I'm thinking of under my bathroom when the tub is full of water!)
I wish someone would do the loading calculation (not my bag).
Laying a single concrete post across the open end of the structure is prob better than having it across the middle.

I have no axe to grid with this, it's just cost, time and effort would seem to be less with timber. Not sure if there is a durability issue tho' although it isn't going to get wet.

Shorter MTTP

(Mean time to Pizza)

Del (sorry if I'm banging on about this )

*A 30mm square section of Yew 6 foot long supported at each end will take my body weight without flexing at all (unless I jump up and down).
Are you making Mexican jumping pizzas?

I have had sagging wood problems in previous houses due to storing junk in the loft. So perhaps I am a bit overcautious.

I guess a filled bath is approaching the same weight as this clay oven, so I will try to remember that. I just wanted it to be solid so I don't have to worry about it and can move on to the next stage. The fence posts have been sitting out in the elements for a year or so, so they are probably a bit wet too. Worst case scenario I can just rebuild the top part. No doubt there will be something I wished I'd done better anyway.

I was hoping the concrete fence post would be long enough to cut in half, but if not I will just put it across the open end like you said.

Shorter MTTP is always better! I'd highly recommend this project to anyone that wants a hobby. It gets you out in the garden and unlike other jobs around the house you have motivation to keep going thinking about all the fires you're going to light and all the pizza you'll be making. I've even got up at 6:30 am a couple of times to do some work on the oven before work. I can't imagine doing the same to clear out the gutters or some other household chore, not exactly the same motivation.

Gotta admit, I love pizza and it have no shortage of fire wood as offcuts from my bow making. Not much spare room in my garden tho'
Yeah, we have a lot of junk in the loft too and a few cracks in the bedroom ceiling.

Be sure to post some pics when its finished. You can always do my jump up and down test on each post and check it for any rot. You've gotta do it how you are happy with it...

Del

I think you've already got the answer with the lintels (the paving blocks will crack if you give them a dirty look, while the lintels are pre-stressed).

But that's only what I think...I've never built one before!

A refractory mix can be made of perlite and cement to place on top of the slab to help insulated it from the heat.

check out 'makezine.com' and 'instructables.com' and search sites for 'clay oven; there are many examples of builds with instructions and cautions.

BTW Where are you? You say "just outside London" but is that London UK?

Even just the continent/country you are on helps.

Del

<cough, splutter> errr, That's Harlow, not as posh as Harrow, but still just round the M25.

Del

(Woo Hoo another UK member who speaks proper like what we does).

I know it's only a fire pit, but this CR4 link is interesting.....

Hmm shows for me. Let me try again a different way.

After sleeping on it I've decided that looks like crap. I've put all this effort in and now I'm being a cheap arse on the plinth.

I phoned up the local builders merchant Travis Perkins and they agreed to do the lintels half price at £5 each. So £65 in total. Collecting them tomorrow.

What doesn't work for one, may work for another.

Some of my projects initially didn't turn out the way I envisioned.

Thanks for sharing, we all can learn from it.

One has to be true to one's self.

But you gotta admit, that wood wan't going to sag now was it.

I'll bet you'll end up with a real nice looking job, and that's half the thing, no point doing a half ar$ed job and regretting it later.

We'll we wanting pics (and Pizza) when it's finished tho'

Del

Your right, I'm sure it wouldn't sag, also I'd expect the wood to dry out and stop rotting. I would always be thinking of it as the weak spot every time I use it though! I'll go back to my original plan of using these posts as fire wood (not for the oven).

If I didn't have the wood spare then it would have cost almost the same as the concrete lintels anyway, so I wouldn't recommend anyone use wood for future projects if it requires going out and buying it.

I'm trying to get it done ASAP as I'm off on a cruise to New York on Wednesday so I'd like to get the first layer of the dome done to let it dry while I'm away Also we just found out recently we have our first baby on the way, so there's only so much time before I get an ear full for messing around with my oven rather than sorting out the baby room. Nothing has been said so far, but you can be sure that point will come some time soon!

I will definitely post pictures when done. I plan to have a nice looking arch at the bottom for the wood store and the blocks will be plastered and painted white. the picture in my head looks good, lets hope the final result is the same.