42" Pizza Build.

[Pizzarotic]

Thanks David,
I'm not sure what the "K factor" is in your chart.
Is this W/mK?

[david s]

Thanks David,
I'm not sure what the "K factor" is in your chart.
Is this W/mK?

No, I’m not sure what units they’re using, there are so many. But it does give a relative comparison of different mixes. You can have strength or insulation value, but not both, so it’s always a compromise.

[Pizzarotic]

If it is Watts per Metre Kelvin then loose perlite is a 10 times better insulator than 5:1 mix. Now my head is spinning. If we can't find a method to work for under floor, I'm thinking 2" loose perlite then 2" of 10:1 over the dome. Could be worth the effort.

[david s]

If it is Watts per Metre Kelvin then loose perlite is a 10 times better insulator than 5:1 mix. Now my head is spinning. If we can't find a method to work for under floor, I'm thinking 2" loose perlite then 2" of 10:1 over the dome. Could be worth the effort.

As I said it is difficult to make comparisons because not only are different units quoted (you can do conversions here)

https://www.engineeringtoolbox.com/t...tor-d_857.html

but the values change for different temperatures. A comparison of thermal conductivity for any given material at ambient may be different at 200C or 400C. eg one material may be an excellent insulator at ambient, but not so good at 400C. Another complication is the grade of perlite selected and which grain size was used to do the testing. Post what you can dig up.

[UtahBeehiver]

This table is from Strong Vermiculite out of the USA (est 1957) so it highly likely that the K values are in Btu•in/(hr•ft2•°F) which make more sense when comparing K values of CaSi

[lowspeed]

Is 1 degree ok? 2,3?

[Sixto]

Its your call, if you are talking about the counter slab level, I think a few degrees won't matter, you can make it up with sand below the floor bricks. If you are talking about the dome, that's round so a course or two off level by 1/2" or so should be fine too, and can also be corrected with mortar.on subsequent courses if you want.

If your chimney is 10 degress off vertical, you might have a visual issue, but you could always call it the tower of Pizza! .

Bottom line is that level construction is what we all strive for, but often fall short, and that's not all that critical to the operation of the oven.

[david s]

The food inside the oven won't care if it's not perfectly level, but if the supporting slab isn't you might end up with water pooling at the base of the dome which can result in water entry to the under floor insulation, so keep an eye out for any cracks at the base.

[Pizzarotic]

Maximum 1.7°

[lowspeed]

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

[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]

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?

[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

[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.

[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]

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]

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?

[Sixto]

Can someone post a picture of the right way to do it? cause it's pretty confusing.

I understood that the best way is to lay down the 9" flat on the narrow part in a circle around the brick floor. So that from the sides of the brick floor you would have 9 inch bricks extending out and then the 2nd layer sits on it.

it would stick out above the brick floor in this case 2 inches. (4.5 brick width -2.5 floor height)

Here's how I did it.

And here is a link to my thread, in case you want to look further... lots of helpful comments to my questions from other forum members... https://community.fornobravo.com/for...inneapolis-wfo

[UtahBeehiver]

If you feel you need to use a soldier then use half height soldiers or use half headers. I would only use a thicker floor if you envision doing lots of bread making. Thicker floors provide more thermal mass but take longer to heat up and use more fuel.

[Sixto]

in the above image it's set as soldiers right? (Sixto image)

https://community.fornobravo.com/fil...etch?id=449790

Yes, my first dome course was a full-soldier, and my floorbricks are a shiner or rowlock in a basketweave pattern. What Russell is recommending is that for most people, a 2.5" thick floor would have enough mass, and then a half-soldier would have less side-thrust since the height and width are the same 4.5". The first course above the half soldier would be 2" above the floor. I fully agree with him, but I wanted more mass in my floor for baking bread. It does take longer to heat it.

[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

[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?