Advice on pouring the hearth

[Neil2]

Re: Advice on pouring the hearth

cecelia

Portland based concrete and vermiculete needs lots of water to cure. When mixing the concrete, use as little water as possible - just enough to make it workable. Then, starting about six hours after the pour, keep it damp continually for at least six days. You can't add too much water at this time. (The people who cast structural bridge girders often submerse the entire girder in a water filled trench for three weeks.) Excess moisture will be driven out later during the firing process once the oven is built.

Most of the home project concrete failures I have seen are the result of not providing continual moisture during the initial curing.

The vermiculete will be cured enough after a couple of days to start laying the hearth and building the dome.

[Matt916]

Re: Advice on pouring the hearth

I have to say, everything Neil has said has been 100% correct. I followed his advice and kept wet towels on top of the vermiculite as it was curing for six days and it seems to have set up very nicely, although very soft and brittle. In one of the pictures that i posted, you can see the top layer of vermiculite-concrete. what you can't see is how it compacts, almost like a sponge, under the weight of the firebrick.
my oven floor isn't laid yet, but after about two days it seemed like it could support weight, although i opted to wait the full six days before i removed the forms and built on it.

I did have one concern with my build though. I laid down this ring of brick just to measure what 42 inches would look like on my hearth, but when i put down the oven landing, it comes right up to the edge of the hearth. Is this ok? in a lot of the pictures i've seen the landing is set back a ways from the edge of the hearth so i wonder if i'll have enough room for a 42 inch oven. I still have to cut the brick so i may be able to move the oven back a few inches. Des anyone have any advice as to what i should do next?

[dmun]

Re: Advice on pouring the hearth

You should be fine: remember, your dome curves in as it goes up so you should have plenty of room for the flue by the six or seventh course.

My dome was quite different, but i ended up supporting one end of the flue tile directly on the dome its self: My oven was a 36 fit into a 5' square, so i was squeezed for space.

If you want a more conventional entry, you can cantilever it out over the edge of your slab, on an overhanging shelf.

[kirshner]

Re: Advice on pouring the hearth

hi I,m building a mobile pizza oven,just finished casting the inner fire dome from a mold,its 2 inches thick in 2 sections and made from 2 parts aluminate cement, 3 parts small river pebbles, 2 part river sand and half part lime.because its on a trailer it seemed safer than using brick,less joins.i,m praying i this mix is adequate,but it was hard to find alternative info to brick work, i,m also thinking of using same mix for the hearth.any suggestions would be great,
thanks

[cecilB]

Re: Advice on pouring the hearth

I have no advice, but I LOVE your question. I, too, would love to know how to make a "homemade" mix for a mobile oven.

Cecelia

[Tscarborough]

Re: Advice on pouring the hearth

I hate to be the bearer of bad news, Kirshner, but I anticipate explosive deconstruction of your dome the first time you fire it to operating temps.

[kirshner]

Re: Advice on pouring the hearth

thanks Cecelia
the hardest part is making a perfect dome so you can plaster the stuff over it,then remove clay from inside and...wallah!.
this i did buy stacking wood blocks into a dome using a jig or stencil as a guide,
I then pressed about 8 20kg bags of clay onto the wood sliding my stencil jig around the base creating a perfect dome.finished it by plastering the mix over it 2 inches thick,now under wet towels.i guess the important part is to keep it a uniform thickness as that will probably decrease the cracks,but i expect they are going to happen anyway.would love some advice on how to add suspension to my steel frame which will be welded onto trailer soon.

[Ken524]

Re: Advice on pouring the hearth

I hate to be the bearer of bad news, Kirshner, but I anticipate explosive deconstruction of your dome the first time you fire it to operating temps.

My curiosity is piqued; I'm trying to figure out why. Can you educate us?

[david s]

Re: Advice on pouring the hearth

Maybe because you did not use any fibres that burn away leaving a network of mini "pipes" to enhance the removal of water vapour. Not sure how the aggregate you used will handle the heat either. Saw lots of ovens in Europe that must be hundreds of years old, many with roughly mortared rocks, they were ok so I think provided you eliminate the water REALLY slowly, you'll be ok.

[kirshner]

Re: Advice on pouring the hearth

thanks for feedback.now i,m freaking out
I got the recipe from a guy online,who makes and sells pizza ovens,river sand and aggregates in my area anyway,are derived from volcanic stone,so should be able to handle the heat.i was intending to dry it out totally before firing it up.thanks david s for th glimmer of hope,but this is frustrating,one person says it will explode another that it will probably be alright.it is special aluminate high temp cement after all and the hydrating lime can handle high temps,so why would it "explode"i if thoroughly dried out.i am sourcing materials that are available as i live in a small country town in new zealand.
cheers