making fire hearth on mobile oven

[kirshner]

hi
my pizza oven is being built on a steel frame placed on a trailer,
at the base of the oven is a steel plate which has a 150 mm high steel collar welded around the edge to support insulation and concrete base.
so I,ve just set the vermaculite 100 mm deep in tray and have 50 mm of depth left in tray for hearth,what i was going to do was fill the remaining 50 mm with a refrack cement mix,then place the dome on it, i would then put the fire hearth inside dome 50 mm deep.
I have premix vesuveus fire cement for this and want to trowel it inside the dome,as fire hearth
here's my question do I have to make it stick to the concrete below with steel pins,as concerned about oven moving in transit,
second Q how do I make the outer imsulation dome attach itself to concrete base as it needs to be a fixed dome for movement as fire dome cant be fixed, but something needs to be for transport reasons.
cheers

[kirshner]

Re: making fire hearth on mobile oven

Hi all
how long do I have to wait for the perlite insulation to set before I can put a slab of concrete over it,I poured it yesterday and its firm to the touch, seems ready but am wondering how the trapped moisture (around perlite) is going to escape once its concreted over

[Laurentius]

Re: making fire hearth on mobile oven

You're doing it wrong. The insulation goes on top of the slab and the hearth floor on top of insulation.

[brickie in oz]

Re: making fire hearth on mobile oven

You're doing it wrong. The insulation goes on top of the slab and the hearth floor on top of insulation.

What he said......
I know we are upside down on the globe but the build method is still the same way.....
Plus, why are you putting heavy concrete in a mobile oven?

[david s]

Re: making fire hearth on mobile oven

From the sounds of it you plan to cast your floor using a refractory castable over the vermicrete insulating slab. This works ok, but expect a large piece of refractory to crack. It is a good idea to at least engineer a join right down the middle so your refractory floor is in at least two pieces. You could set a few pins into the floor that will key into the base of the dome when you cast over the floor. I didn't do this for my mobile oven and the only thing that holds my one piece cast dome in position is gravity and the vermicrete insulation surrounding it. It has not led to any problems though. Assuming when you said slab of concrete that you meant refractory concrete (castable)

[brickie in oz]

Re: making fire hearth on mobile oven

I have premix vesuveus fire cement for this and want to trowel it inside the dome,as fire hearth

It wont work, that is just a thin joint glue for sticking fire bricks together with.

[david s]

Re: making fire hearth on mobile oven

It wont work, that is just a thin joint glue for sticking fire bricks together with.

It depends what Vesuvius product he has, they make a wide range of refractory products including castable refractory. He may well have the correct one.

[kirshner]

Re: making fire hearth on mobile oven

thanks for the replies,
A few things to explain,
I realise that a concrete slab usually goes under the insulation as a base for it to sit on,I didnt think it was necessary here because the base of my structure is a thick steel plate,very heavy cant remember exact width.
this plate is above the wood storage area, its high so wont touch the wood.
so on the plate i have 100mm deep of vermaculite, on that I have a 50mm concrete slab which is made from a refractory cement the mix designed for heat and strength.
and finally on top of that I have 50mm deep of vesuveus premix as the fire hearth,
this premix was recomended to me by a company that makes ovens and it is what they used to make firewall domes,its not the joint compound.
this suff was expensive ,would never just use plain concrete.
thanks david I will do it in 2 halves,and use the pins
under all those layers how hot do you expect the plate to get realistically isnt the vermaculites job to keep that heat to a minimum,plus the wood entrance will be open to the air

[Laurentius]

Re: making fire hearth on mobile oven

The Vcrete will be as effective as its thickness and consistency are properly maintained. Too thin a layer or too compacted, its almost useless.

[kirshner]

Re: making fire hearth on mobile oven

when you say,Vcrete I assume you mean the vesuveus concrete not the vermaculite and concrete,
if so interesting point about not making it too compact will check it out
thanks.I have some spare ceramic insulation blanket which I might strap under the steel plate if it heats up to much

[Laurentius]

Re: making fire hearth on mobile oven

I meant vermaculite, I'm not familiar with vesuveus. Are you using the steel plate as a reservoir for heat or for structural stability? If you are not using it for heat, I would place the ceramic blanket on top of it to minimize the heat transfer.

[david s]

Re: making fire hearth on mobile oven

With 100mm of dense refractory castable sitting on top of ceramic fibre blanket it is likely to just compress it, your 100mm of vermicrete should be sufficient insulation on its own. Use a 5:1 vermiculite, cement ratio and let it dry for about 3 weeks before building over it.

[Laurentius]

Re: making fire hearth on mobile oven

Wouldn't you say "A ton of Bricks", also compresses the ceramic boards, upon which its sit? Isn't the (maxim) here is: Insulate, insulate, and insulate????

[david s]

Re: making fire hearth on mobile oven

Yes, board might be ok but blanket is too soft. 100 mm vermicrete is sufficient. He's also using castable, not bricks

[kirshner]

Re: making fire hearth on mobile oven

thanks for the healthy debate
I will get some fibre board to go on top of vermaculite before i cast hearth then,
do I really have to wait 3 weeks for vermaculite to dry before I cast floor,because then I will have to wait another 3 for hearth to dry,I want to use it in 4 weeks.
dome has been drying now for 3 weeks.