another hearth question

[PizzaJNKY]

Hello everyone. I hope you're all having a good weekend. As for me, I have been busy building my oven. I have just poured concrete down all of the block wall cores, and have framed for the hearth, using 2x8's. The rebar is all set for the structural layer also, which I plan to make 3-1/2 inches thick. The insulating layer will be 4" thick, made of portland cement mixed with perlite.

I am following the FB plans for the Pompeii oven 42". I am not quite sure of the process for pouring the two layers for the hearth. Once I pour the structural layer, can I immediately start with the insulating layer, or do I have to wait a few days for the structural layer to cure?

Thanks in advance for any suggestions.

[Les]

I recall that the plans wanted you to pour them together, I really don't think it would matter either way. Most of us have gone to the insulation board for simplicity - sounds like you are committed, so go for it. Good luck and welcome to our obsession.

Les...

[thebadger]

PizzaJNKY

Les isrigh. The plans called for everything to be poured at once (same day). But most seem to do it in two parts. I just poured my hearth yestarday and will pour the insulating layer next weekend. I think the concern was you didn't want a "cold joint" but given the weight of the oven - nothing is going to shift.

Dick

[PizzaJNKY]

Thanks for the advice. If I can, I will do both tomorrow. Originally, I was not going to begin this project until May, when I start my 3 week vacation. I ended up starting sooner, working every weekend. I figured if I can finish the oven before I start my vacation, I can relax for 3 weeks and eat lots of pizza, instead of work my tail off. Good luck with your project badger.

[RTflorida]

badger is correct, the original idea was to have the 2 slabs bond together....pour the support slab, wait a couple of hrs, then the insulating slab. This is how I did mine; others since have poured on separate days with no ill effects, as badger mentions - there is a whole lot of weight that ends up on top, there isn't going to be any movement between the two (at least not any that has been varified).

RT

[gjbingham]

I'd recommend six inches of insulation for the floor vs. four. Or just 4 vermicrete and an inch or two of ceramic board over that. My biggest bitch about my oven is that the floor doesn't hold heat as well as the walls. (I used four inches of vemiculite/concrete).

[PizzaJNKY]

Thanks Bingham. I do plan on adding at least 2" of FB board ontop of the 4" insulating layer. I guess I better order the FB board soon.

[Xabia Jim]

Originally Posted by gjbingham

I'd recommend six inches of insulation for the floor vs. four. Or just 4 vermicrete and an inch or two of ceramic board over that. My biggest bitch about my oven is that the floor doesn't hold heat as well as the walls. (I used four inches of vemiculite/concrete).

I think you're right here GB

Since the hearth is your cooking surface, you want it hot and to stay hot. I added insulation under mine after it was done for the same reason. I may put a door on the wood storage area just to help hold just a bit more!

Now how much do you want thermal mass in the hearth and how much insulation? Would you consider two layers of firebrick overkill? Certainly not overkill to do two layers of FB board though, just more costly right?

[Dutchoven]

JNKY
Anytime within 24 hours is fine...no need to push yourself and try to do both at the same time...even within the week is fine...don't finish the structural slab until it shines. just get it smooth and level...it will make boxing out the vermicrete much easier.
Best
Dutch

Originally Posted by PizzaJNKY

Thanks for the advice. If I can, I will do both tomorrow. Originally, I was not going to begin this project until May, when I start my 3 week vacation. I ended up starting sooner, working every weekend. I figured if I can finish the oven before I start my vacation, I can relax for 3 weeks and eat lots of pizza, instead of work my tail off. Good luck with your project badger.

[gjbingham]

XJim,
Good question about the double layer of bricks on the oven floor. Perhaps even the half-thickness bricks? That would make the thickness of the floor almost as thick as the walls - somewhere around 4 inches thick. That would certainly help with heat retention. I wonder how much more fuel it would take to get the floor up to pizza temps?

What do you think? It would be relatively easy to place another temporary layer in there and test it out, huh?