38" Pompeii build

[Frenchie]

Working only with a brick bolster and a 9” grinder has its limitations so my cuts are not the most accurate or clean. I’ve been getting by though, using wedges to plug big gaps between bricks in a course and sometimes between courses.

on the last course I’ve tapered and bevelled the bricks but as we get closer and closer to closing the dome I’m afraid much of the material will be mortar or screed and not firebrick.

Therefore I have lapped 2 layers of full bricks together in opposing directions to prefabricate a keystone. The bricks were ‘keyed’ before joining with mortar. I will cut the 4-brick block down to suit the final opening in an attempt to minimise mortar. Will it be okay?



I plan to handle this keystone by drilling in plugs and fashioning a handle, the plugs later to be removed and mortared

[Frenchie]

Keystone has been marked, cut and trial-fitted.
ready for aesthetic fettling and mortar tomorrow, and a few tapered wedges on the cardinals.

[mongota]

It's always a great accomplishment to get the dome plugged. Congrats in advance on getting that cap wedged and mortared in place.
Just when you celebrate that feat, the real work begins!

[Frenchie]

Haha, yes there’s much much to do. One suspects such a project is never truly completely finished

[Frenchie]

Cleaned up yesterdays joints best I could - left them a little too long

[rsandler]

Congrats on closing your dome!

If the excess mortar is bugging you, scrubbing with vinegar and a wire brush can remove stubborn excess bits of mortar (one can use stronger acid, but using HCl or muriatic in an enclosed space gives me the heeby-jeebies. YMMV)

[Frenchie]

I found a few hours last saturday and managed to build the outer arch.

For the chimney transition, I was going to build a brick platform on top of the arch to create a level surface - HOWEVER, I just can't cut the bricks properly - so will save the remainder of my firebricks for an outdoor barbecue or firepit.

Instead of the bricks I will cast a flat plinth in-situ using either Vitcas Heatproof Screed, or Refractory Castable.
Then on top of this, I will place my transition piece.

The transition piece will use a rectangular to round duct converter as a form, making the transition out of castable refractory.

[Frenchie]

If one uses 3 layers of 1" fibre blanket insulation, is the v/p-crete layer still required or can we go straight to stucco on top of the insulation?

If the v/p-crete is required, what thickness on say, 2" or 3" fibre blanket please?

[Giovanni Rossi]

I believe you'll find the stucco/render is easier to apply over the pericrete vs. over the blanket for a few reasons. The springiness of the blanket make it difficult to trowel a smooth layer of stucco unless you are quite skilled. The stucco layer is not so thick and will make it difficult to get a smooth layer over the lumpiness of the blanket. Plus, the blanket will pull moisture from the stucco, decreasing working time.

The same issues pertain to the pericrete. Some builders have been successful at using one thick layer of pericrete, but that has its challenges in getting the right consistency to prevent slumping while maintaining the dome shape.

Most use thin layers of pericrete that can be troweled on quickly. After the first layer, each subsequent layer allows for working the surface to correct/maintain a proper dome shape.

I don't think there's any hard and fast rule for the final thickness of the pericrete. It can depend on how much room you have on your slab and the look you're trying to achieve. I was trying to maximize my dome insulation and had planned for 2 inches over my 4" of blanket. I did it in 3 layers and that seemed to work fine. I probably finished with a bit more than 2". I'm not that skilled with a trowel, but I was able to get a good result. Take a look at my build. I believe it was david s who suggested using a wire brush lightly on each layer before it cured to provide a good substrate for the next.

[Frenchie]

I believe you'll find the stucco/render is easier to apply over the pericrete vs. over the blanket for a few reasons. The springiness of the blanket make it difficult to trowel a smooth layer of stucco unless you are quite skilled. The stucco layer is not so thick and will make it difficult to get a smooth layer over the lumpiness of the blanket. Plus, the blanket will pull moisture from the stucco, decreasing working time.

The same issues pertain to the pericrete. Some builders have been successful at using one thick layer of pericrete, but that has its challenges in getting the right consistency to prevent slumping while maintaining the dome shape.

Most use thin layers of pericrete that can be troweled on quickly. After the first layer, each subsequent layer allows for working the surface to correct/maintain a proper dome shape.

I don't think there's any hard and fast rule for the final thickness of the pericrete. It can depend on how much room you have on your slab and the look you're trying to achieve. I was trying to maximize my dome insulation and had planned for 2 inches over my 4" of blanket. I did it in 3 layers and that seemed to work fine. I probably finished with a bit more than 2". I'm not that skilled with a trowel, but I was able to get a good result. Take a look at my build. I believe it was david s who suggested using a wire brush lightly on each layer before it cured to provide a good substrate for the next.

Thank-you for this reply, good insights and your approach sounds like something I will replicate - although I only managed 3" blanket vs your 4 - 2" of P/V'crete on top sounds achievable, both in terms of the materials to hand and space remaining on the slab! Out of interest, how long did you wait between pericrete layers? Given the rapid decline in temperatures and availability of dry days, it would be good to get all the work done in 1 day, although it is perhaps more realistic to expect to lay 2 layers is 1 day and not 3!

[Frenchie]

The weather is closing in on us! Needing to make the most of the odd dry and warm-ish hour or two here and there when not working or having family commitments.

The oven is now insulated with ceramic blanket and supported with wire. It needs chicken wire then v-crete layer before rendering.
The chimney begins with a cast plinth on top of the arch using refractable. On top of this is a rectangular to round duct adapter (steel), then the stainless flue pipe.

The ceramic blanket is applied in 3 layers, when covering with V-crete the material will be sculpted around the chimney. The outer arch is isolated so doesn't need to be fully covered by ceramic blanket.

The entrance in the outer arch is temporarily firebricks - it will be V-crete with a stone slab. The floor will be isolated with insulating glass fibre tape.
The dome and outer arch are constructed with 8mm air gap, the gap is filled by folding over 50mm x 3mm ceramic fibre tape. Friction only keeps it in place. I think this should be sufficient and it can compress without the dome loading the arch when the dome is hot. If the tape falls out, high temp sealant could be applied to one side and it be pushed back in. Lets see

I have had 2 no. small curing fires of 2 to 3 hours, top of dome reaching c. 150 to 175C.

[JRPizza]

Hey Frenchie, as an alternate to using pericrete you could consider using a steel mesh/lath like I did. The stucco will stick to it well and you can get the shape of the dome nice and round with the lath if you cut and tie it right. Here is a link to what I did if you are interested.

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/pompeii-oven-construction/380308-39-inch-corner-build?p=388015#post388015

[Frenchie]

Hey Frenchie, as an alternate to using pericrete you could consider using a steel mesh/lath like I did. The stucco will stick to it well and you can get the shape of the dome nice and round with the lath if you cut and tie it right. Here is a link to what I did if you are interested.

https://community.fornobravo.com/for...015#post388015

Hi JRPizza thank-you for the suggestion! I had naively assumed the v/p-crete was belt and braces insulation, as well as for bonding stucco. But if good lath can remove some materials and steps then I am all in favour!

what happened at the top of the dome with your lath, did you trim it or did it just overlap? It looks very tidy indeed, far superior to chicken wire!

[JRPizza]

It was one of the many things that I had no idea of what I was doing when I started but turned out OK. There are probably more elegant ways to cut the lath but I just did the ~5.5" cuts down to where the sides of the dome got kind of straight near the bottom, then just wrapped the sections around the top tight. I don't think I trimmed them. I can't remember how I sequence them but I might have done a few opposite sides to tighten it down and then went around in a circle. I tied it with the wire used for tying rebar forms. You can see in the pictures how there is little overlap near the bottom of the mesh and lots near the top. I think I used this " RELIABILT 27.5-in x 8.5-ft Galvanized steel Stucco Netting" that I picked up at the local box store.

[JRPizza]

Here is a shot where I started gathering up the sections towards the top of the dome. They almost wrapped themselves!