42" Pizza Build.

[Sixto]

The blocks are 2.5x4.5x9 inch

I want to clarify, you're saying 9inch going up is fine as long as they are set going around the surface bricks but with narrow side touching the surface of the bricks?

Hi lowspeed, I built a 36" diameter dome with soldiers that are just mortared on the sides, but not at the bottom (used newspaper to avoid bonding to the insulating bricks below) I angled the tops to match the Amgle made by the IT. It all seems to be holding fine after the drying fires. My herringbone floor is floating on a sand and clay dust base above insulating firebrick base, and separated from the soldier course by a 1/4" corrugated cardboard spaceR . Also note is that my floor is 4.5" thick because I want to bake bread on day 2. So the first course of dome bricks is somewhat less than 4-1/2" above the top of the floor.

[UtahBeehiver]

That is a soldier brick and as David mention there are horizontal loads that may require buttressing of the soldiers.

[lowspeed]

The blocks are 2.5x4.5x9 inch

I want to clarify, you're saying 9inch going up is fine as long as they are set going around the surface bricks but with narrow side touching the surface of the bricks?

[david s]

Laying the blocks on edge results in a mortar joint that is not wide enough for structural stability. The standard brick thickness is 4”, but laid on edge would be 3”. I don’t know what size your fire bricks are as there are many different sizes, but for structural building a 4” wide mortar joint is considered standard, as in house brick walls, 3” not structural. Remember also that as the oven is subjected to thermal expansion, any structural problems are magnified.
The dome can be laid either sitting on the floor bricks or sitting outside the floorbricks, but either way the oven must be insulated under. The first course is usually not mortared to the floor.
soldiers (definitely not sailors) for the first course are asking for trouble IMO because you are placing a tall vertical joint right where any cracking is likely to begin, at the weakest part of the he dome. Think of an eggshell cut in half. What is the weakest part, and where cracks are likely to develop.Builders are careful to stagger the vertical joints so none line up. A soldier course is doing exactly that, by laying the first course the height of two half bricks.

it is difficult to see how thick your vermicrete under floor insulation is, but a 5:1 vermicrete should be 4” thick to adequately insulate under the floor. As yours does not seem to extend out past the floor, you’d probably be better to lay the first dome course on top of the floor.

The typical low domes of the Naples style ovens would have very little height at the base of the dome inside, so use a soldier course, but as the large radius, low dome exerts a lot more sideways thrust on the soldier course it is either braced with a steel band around the outside of the soldier course, or it is buttressed by an extra layer bricks. Whereas the more structurally sound hemisphere is self supporting.

[lowspeed]

Full soldiers are more prone to horizontal pressure from the dome above and may require buttressing of the soldier course. Half soldiers or half header would be better

What about sailors? I actually am planning to put the narrow side all around

[UtahBeehiver]

Full soldiers are more prone to horizontal pressure from the dome above and may require buttressing of the soldier course. Half soldiers or half header would be better

[lowspeed]

1) would using full size soldiers be ok or should i make them shorter?
2) do you cement the soldiers to the floor (in this case perlite cement) or do the firebricks? or not at all they just cement to each other in a circle?

[Pizzarotic]

I doubt that would work very well. Most of the heat would be lost into the atmosphere. You could tent it with an electric heater or heat lamp from above but I would put a heat source underneath, either an electric heater or small propane burner and warm the slab up and let it transfer through to the perlite. That should hurry it along.

[david s]

I wouldn't advise salt because it will dissolve if it gets wet.and turn to mush Where we live 9Humid tropics) people put rice in their salt shakers otherwise the humidity in the air just clogs them up.

[lowspeed]

After perlite cement cures, is it possible to dry out the slab by placing fire bricks on top and staring a fire?

Say bricks that cover 1/3 of the area.

[Pizzarotic]

Quite possibly, it has a high enough melting point. Traditionally people used what was available locally so it could be salt or maybe even silica sand. Either would work.

[david s]

When the surface appears dry you can be sure that it will still be moist deeper in. Like a pile of sand that remains moist deeper in for months, when it appears dry on the surface. A cheap garden moisture meter is a pretty good tool for this purpose.
See my experiment on weighing an insulating slab to measure its drying.

Weep holes through the supporting slab do a good job of allowing the moisture to escape as it runs away from the heat source. If not already cast into the slab they can be drilled, or if the insulating slab is already cast over the supporting slab, they can be drilled from underneath.

I've done a few repairs on ovens that had no underfloor weep holes and the recommended build had called for marine ply over a steel stand. Accumulated water in the underfloor insulation had nowhere to escape, so consequently sat there, rotting the plywood floor. Half a dozen1/2" holes drilled through the mushy ply floor allowed the moisture to escape restoring oven performance once it all dried out.Heat and moisture is a bad combination for steel and wood and for this reason is best avoided for ovens.
Vermicrete insulating slab PDF copy.pdf

[lowspeed]

Also is there a good way to check when the perlite cement is dry and no longer storing moisture?

Also... would you recommend weep holes around where it meets the concrete?

[lowspeed]

Typically floors are not mortared or set in mortar. This allows the floor bricks to expand and contract. If leveling in required a mix of 50% sand and 50% fire clay is used as a leveling medium. It is spread out with a notched trowel and brick set in and leveled with a rubber mallet.

Any reason not to use 100% fire clay? why mix with sand?

[lowspeed]

Plot twist. Someone pointed out to me that the white stuff in the video is actually salt....