Need help with my next steps.

[Omaharosario]

Just Finished the the stand and the have poured a 4" reinforced concrete slab for the 1st layer of my floor.
What to do next? Please give me your input on the best way to finish the next couple of pours before our dome. Thanks!

[Neil2]

Re: Need help with my next steps.

1. Keep it continuously damp and covered for at least 7 days.

What type of under hearth insulation are you planning for ?

[Faith In Virginia]

Re: Need help with my next steps.

Your next layer is either the Portland/ Vermiculite or insulation board. So insulation is the next step.

[Neil2]

Re: Need help with my next steps.

Next, examine your new structural slab closely. Patch any voids in the top and sides.

The slab should also drain freely - no standing water. If necessary, grind the surface so as to eliminate or drain any low spots. Water will get into your oven from time to time so you should plan for it. If there is any "bathtub" it will be difficult and time consuming to dry out.

Layout on the slab the footprint of your oven and entryway. Allow for the brick thickness and for the thickness of the dome insulation.

If going the Portland/vermiculite route, form up on the slab for this shape. (You can use the existing form work to attach blocks to support the form work for the insulation layer). The shape does not need to be exact and can be a bit wider, however the insulation layer should not extend out to the edge of the structural slab, if it does this will be an entry route for moisture in the future.

You should keep your new structural slab continuous moist during the forming and pouring of the insulation layer. The insulation layer in turn should be kept moist for at least 7 days.

If going the insulation board route you need to have a flat surface under the oven footprint (still draining) to support the board. Leveling can be done with a thin layer of sand. Place your insulation board and continue.

[Omaharosario]

Re: Need help with my next steps.

Under the hearth for the footprint we plan on using a type of refractory insulating cement.
Not to sure if one is better then the other or the price difference. Any thoughts?

[Neil2]

Re: Need help with my next steps.

"a type of refractory insulating cement"

Not sure what this might be. Most builders here have either used a vermiculite (or perlite) / Portland cement mix of 5:1 or have used insulating board.

If using the vermiculite / cement material a thickness of 4 inches is recommended.

[RTflorida]

Re: Need help with my next steps.

Sounds to me as if someone has not thoroughly read the Pompeii oven plans. If you have not, NOW is the time. You are at the point where using an ill suited material can make the difference in owning a fantastic cooking vessel or simply a tool for adding to global deforestation (you will burn a huge amount of wood and never hold the temps that you want).

You next step should be one of three options and nothing else:
1) 5:1 vermiculite/portland cement mix (4" thick)
2) 5:1 perlite/portland cement mix (4" thick)
3) Minimum 2" of refractory insulating board. Many manufacturers and various compositions, available in the Forno Bravo store if you can't find a local supplier.

RT

[dmun]

Re: Need help with my next steps.

We have repeated problems with wet pre-mixes. They are made, as the man says, for boilers, where there are tiny, well fitted, joints, and they are completely isolated from any dampness. If your firing chamber doesn't reach those temperatures, the mortar never sets, and remains water soluble. If you must use a commercial refractory mortar, use a dry mix used for fireplaces, such as heat-stop50 or equivalent.

[Omaharosario]

Re: Need help with my next steps.

Thamk you this is very helpful

We have repeated problems with wet pre-mixes. They are made, as the man says, for boilers, where there are tiny, well fitted, joints, and they are completely isolated from any dampness. If your firing chamber doesn't reach those temperatures, the mortar never sets, and remains water soluble. If you must use a commercial refractory mortar, use a dry mix used for fireplaces, such as heat-stop50 or equivalent.

[Omaharosario]

Re: Need help with my next steps.

My local supplier at "The Plibrico Company" suggested I use his product which is a pre mixed refractory cement that he uses for boilers that reach in excess of 2000 degrees if I am not mistaken. As far as not reading the Pompeii directions what part would you be referring to? Because I am just trying to use everyone else's experience along with the Pompeii directions to have the best knowledge in going forward with my project.

Sounds to me as if someone has not thoroughly read the Pompeii oven plans. If you have not, NOW is the time. You are at the point where using an ill suited material can make the difference in owning a fantastic cooking vessel or simply a tool for adding to global deforestation (you will burn a huge amount of wood and never hold the temps that you want).

You next step should be one of three options and nothing else:
1) 5:1 vermiculite/portland cement mix (4" thick)
2) 5:1 perlite/portland cement mix (4" thick)
3) Minimum 2" of refractory insulating board. Many manufacturers and various compositions, available in the Forno Bravo store if you can't find a local supplier.

RT

[Omaharosario]

Re: Need help with my next steps.

Wanted to see what the best type of all around product for my foot print is, type of portland ratio mix or insulation board. I would like to be able to reach higher temps and have a extended amount of cooking time. Thanks!

[brickie in oz]

Re: Need help with my next steps.

I used insulation board for my build, the vermicrete mix seems like a lot of effort when you can buy a beard for probably the same price.

For extended cooking you need more thermal mass and more top insulation.

[RTflorida]

Re: Need help with my next steps.

You mention, "the best way to finish your next couple of pours before the dome".

How to finish? no clue what you mean here.

Next couple of pours before the dome? Unless your plan is to go off the reservation with a new design concept, I believe the Pompei plans clearly tell you that the next step (on top of the reinforced hearth slab) is to install an insulation layer of the materials several of us have mentioned.
I'm not trying to be argumentative, but what you propose is not something that is mentioned in the plans and your initial statement leads one to believe that you don't know what to do next.
The use of a refractory insulating cement for the insulating hearth layer has not been done by anyone that I remember. Even those who have "cast" there entire ovens out of castable refractory, typically use one of the 3 mentioned types of insulation. I think you will find any castable refractory (which is what you would need for such a great thickness) to be very costly, with insulating castable being the most expensive.

RT

[david s]

Re: Need help with my next steps.

I just made a vermicrete insulating slab tonight. It took just over a third of the total volume in water. If I were to place a floor straight over this it will hold that water in and create problems removing it later at the curing fires stage. Much better to take your time, let the weather dry it, if possible. In my case I will store it and weigh it in a few weeks time and work out how much water it still contains. The beauty of using insulating board is that you don't have this water removal problem. The water under the oven floor is the hardest to get rid of.

[Omaharosario]

Re: Need help with my next steps.

Thanks! I think using the insulating board will work the best for me on my first oven.

I just made a vermicrete insulating slab tonight. It took just over a third of the total volume in water. If I were to place a floor straight over this it will hold that water in and create problems removing it later at the curing fires stage. Much better to take your time, let the weather dry it, if possible. In my case I will store it and weigh it in a few weeks time and work out how much water it still contains. The beauty of using insulating board is that you don't have this water removal problem. The water under the oven floor is the hardest to get rid of.