Need help with my next steps.

[Omaharosario]

Re: Need help with my next steps.

I had many of the same questions when I was choosing a refractory mortar. I discovered that air set (premixed wet) mortar is water soluble, meaning if it gets wet after it has dried it will again be workable, hence it could easily be damaged . Only use mortar that 'cures' (powder form), not air drys, and moisture will have no effect on it once cured . See Build Masonry Fireboxes for a good explanation.

gene

Thanks Gene! That was very helpful in helping me understand why this product is not suggested. Also what kind of mortar did you end up using?

[ggoose]

Re: Need help with my next steps.

I had many of the same questions when I was choosing a refractory mortar. I discovered that air set (premixed wet) mortar is water soluble, meaning if it gets wet after it has dried it will again be workable, hence it could easily be damaged . Only use mortar that 'cures' (powder form), not air drys, and moisture will have no effect on it once cured . See Build Masonry Fireboxes for a good explanation.

gene

[Omaharosario]

Re: Need help with my next steps.

So have you heard bad things about this product?

[Ken524]

Re: Need help with my next steps.

You don't want to use rebar in the insulation layer.

Has anyone used a refractory mortar called "Super Demon Air Set"? If you have, do you have any positives or negatives of this product.

Please read DMUN's comments concerning premixed wet mortars on the previous page. There are better products out there for a Pompeii.

I would like to be able to reach higher temps and have a extended amount of cooking time.

What do you mean by this? The standard Pompeii oven will hit 1000F and provide usable cooking heat for nearly 3 days after firing. Do you have a goal in mind that exceeds this?

[Omaharosario]

Re: Need help with my next steps.

Has anyone used a refractory mortar called "Super Demon Air Set"? If you have, do you have any positives or negatives of this product.

[mrchipster]

Re: Need help with my next steps.

For a 4" pour of 5 to 1 ratio vermiculite-portland, what type of portland is suggested??
N, S, O, or other. Also should rebar be used in this layer?

Portland cement is not graded with letters Mortars are graded with letters.

You do not want mortar you want Portland cement.

Mix by volume and not weight. I used a kitchen 1/2 gallon pitcher to make my mix. Of course it took more than 5 scoops of vermiculite an one scoop of cement.

Wet the vermiculite with about 1/2 - 3/4 gallon of water per cu ft of vermiculite then mix up a slurry of portland cement and water, thick soup like tomato soup consistency. Then pour the slurry evenly into the wet vermiculite mix with a shovel until it reaches a consistent color. after that shovel into your forms.

Do NOT!!! use a power mixer it will break down the vermiculite.

Chip

[Omaharosario]

Re: Need help with my next steps.

For a 4" pour of 5 to 1 ratio vermiculite-portland, what type of portland is suggested??
N, S, O, or other. Also should rebar be used in this layer?

[Neil2]

Re: Need help with my next steps.

Any portland based concrete needs lots of water to cure. After it is cured (at least 7 days) then it will start to dry. Final drying can wait until the dome is built. Drying out the oven completely takes time and patience but is not that difficult.

[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.

[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.

[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

[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.

[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!

[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.

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.