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Offline Pod4477

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #120 on: May 10, 2019, 11:16:35 AM »

Going to sound like a broken record here... but these are things I would want to know before starting.

In my stand, I went overboard. My walls are tied to the bottom slab with rebar. I did the corners and every other hole. A piece of bar goes down every hole I filled. Those bars were long enough so that they could be bent and combined with the top slab rebar. I basically made a reinforced concrete box.

I stuffed portions of the bags that the concrete used to fill the cores came in to plug the unfilled cores so the slab concrete didn't go all the way down those holes. If you are capping and filling the stand with sand, this doesn't matter because there is no slab. If there is no slab, personally I would at least fill every other hole  in the the block and the corners. If you do the running bond, this will ties the stand together. Having rebar in the filled cores will make it stronger. With the right tools, half inch rebar isn't hard to cut. With a hack saw, it grows old fast.

Haha, yup you're very right.  I'm going to finalize and make decisions in the next day, but I know the construction of the stand will take a few days, especially with rain today.  Tying in the slabs and walls is genius and something I should have done.  I have been getting pretty good at using the angle iron with the diamond blade, so I'm happy to not have to use a hacksaw for it, because I know that is what I would have used prior to buying the angle iron.  Filling only the corners seems like a risky idea, so every other hole it is for sure.  I may even stucco after, as well, for added insurance.  I have a ton of rebar left over from the slab.  So I pretty much just drop one rebar in every other hole and corners, making sure it isn't too long that it comes up the top (cut it if it is), and then fill with concrete? 

Also, what consistency did you use to fill?  Forno Bravo says to mix a wet batch and put it in buckets to make it easy to pour into the cores; they don't mean literally making it extra thin and runny, probably just mixing with water before using buckets in a regular consistancy I'm assuming?
« Last Edit: May 10, 2019, 11:23:37 AM by Pod4477 »

Offline Jon in Albany

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #121 on: May 10, 2019, 11:41:08 AM »


Haha, yup you're very right.  I'm going to finalize and make decisions in the next day, but I know the construction of the stand will take a few days, especially with rain today.  Tying in the slabs and walls is genius and something I should have done.  I have been getting pretty good at using the angle iron with the diamond blade, so I'm happy to not have to use a hacksaw for it, because I know that is what I would have used prior to buying the angle iron.  Filling only the corners seems like a risky idea, so every other hole it is for sure.  I may even stucco after, as well, for added insurance.  I have a ton of rebar left over from the slab.  So I pretty much just drop one rebar in every other hole and corners, making sure it isn't too long that it comes up the top (cut it if it is), and then fill with concrete? 

Also, what consistency did you use to fill?  Forno Bravo says to mix a wet batch and put it in buckets to make it easy to pour into the cores; they don't mean literally making it extra thin and runny, probably just mixing with water before using buckets in a regular consistancy I'm assuming?

That's all the bar is. You can also use the bar like a tamping rid to help pack in the concrete into the core.

I mixed to the quickcrete package directions. Some extra water won't hurt but really over doing it will separate the stone from the paste and start to reduce the final cured strength.

Offline Pod4477

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #122 on: May 10, 2019, 11:58:54 AM »

That's all the bar is. You can also use the bar like a tamping rid to help pack in the concrete into the core.

I mixed to the quickcrete package directions. Some extra water won't hurt but really over doing it will separate the stone from the paste and start to reduce the final cured strength.

Thank you for the quick reply.  That is a good idea to use it for tamping.  Yeah I learned my lesson doing patching to never use too much water.  I've been getting more used to consistency, but I really should properly mix to the bags' ratio.  Did you use the Quickcrete High Strength Concrete in the yellow bags?

Offline Jon in Albany

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #123 on: May 10, 2019, 12:09:48 PM »
Just the regular quickcrete. I got the smaller bags to spare my back. Cost was basically the same.

Offline Pod4477

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #124 on: May 11, 2019, 12:51:23 AM »
Just the regular quickcrete. I got the smaller bags to spare my back. Cost was basically the same.

That's what I've been using too, but didn't check last time to see if they came in 50 or 60 lbs.  I picked up the rest of the block today!  I plan on stacking and filling the cores today.  We have some more rain on the way after tomorrow, but I'll make a decision on sand vs wooden supports in the next day or two.  I just want to get the stand done while the first course if level.  I have more experience dealing with sand/earth and tamping, but I'm sure I could do wooden framing.  For the top slab, I'm wondering if I need two different layers (concrete with rebar and then perlcrete) or if I should just do one 2-4" perlcrete layer.  I assume the added support is always good, but the book only used the 2" perlcrete slab.  What do you think?

Lastly, I came across this article https://www.mugnaini.com/2016/07/insulation-or-thermal-mass/; in the last paragraph they talk about refractory concrete for the slab.  Has anyone ever tried using refractory concrete for thermal mass?  So if I understand right, perlcrete and Fb board work in similar ways, by stopping downward heat, holding some heat and pushing heat back up to the firebrick.  Refractory concrete holds heat which basically keeps the firebrick hot as well.  Do you guys think insulation or thermal mass is a better way to handle what happens below the firebricks?
« Last Edit: May 11, 2019, 01:45:18 AM by Pod4477 »

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Offline Pod4477

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #125 on: May 12, 2019, 10:28:22 AM »
Update: 4 courses are done and every other core filled, making sure to do the corners and so every block has at least one core filled.  We have about 3 days of rain ahead so I covered it with a tarp. In the next 3 days I need to decide whether or not I mortar on block caps or do a wood frame and have the slab cover the cores. I also hope the first course leveling mortar will be ok in the rain. Itís been about two days so Iím assuming it would be fine.
« Last Edit: May 12, 2019, 10:31:25 AM by Pod4477 »

Offline scott r

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #126 on: May 12, 2019, 11:42:10 AM »
Do you guys think insulation or thermal mass is a better way to handle what happens below the firebricks?

When I first opened my pizza truck five years ago the oven in it had a single layer of WG firebrick for the floor with insulation directly under that.  When it was preheated properly it was plenty of thermal mass to make 150 pizzas in succession with the floor blanketed for two hours without loosing the floor.  For a home oven you will never need any more thermal mass than what your floor will give you so I would just put some calcium silicate under your firebrick floor.  If you put any thermal mass under there its just going to take you forever to preheat the oven to the point of full saturation (which is what your going to want for really great bakes).
« Last Edit: May 12, 2019, 11:58:08 AM by scott r »

Offline Pod4477

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #127 on: May 12, 2019, 07:21:00 PM »
When I first opened my pizza truck five years ago the oven in it had a single layer of WG firebrick for the floor with insulation directly under that.  When it was preheated properly it was plenty of thermal mass to make 150 pizzas in succession with the floor blanketed for two hours without loosing the floor.  For a home oven you will never need any more thermal mass than what your floor will give you so I would just put some calcium silicate under your firebrick floor.  If you put any thermal mass under there its just going to take you forever to preheat the oven to the point of full saturation (which is what your going to want for really great bakes).

Thank you and wow thats a lot of heat retention! So perlcrete would be similar to calcium silicate, just less efficient per inch?  I also forgot that making a closed stand means I can't make a wooden form support, as there's no way to get it out.  So looks like I'm set on:
a) filling it in with sand, using block caps and filling without frames by screeding across the block caps
b) mortaring concrete lintels to span across the blocks
c) use wood frames and pour 2-3" concrete followed by 2-3" perlcrete over the sand and cores.  This will give me even more height than block caps, if I do 6" total concrete/perlcrete. So for the wood frames, shims are used in between the legs and frame  or under the feet, to level?  I've also seen strapping used.
« Last Edit: May 12, 2019, 09:35:56 PM by Pod4477 »

Offline scott r

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #128 on: May 12, 2019, 09:40:48 PM »
So perlcrete would be similar to calcium silicate, just less efficient per inch? 

yes, both will insulate under the floor

Offline Pod4477

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #129 on: May 12, 2019, 10:49:16 PM »
yes, both will insulate under the floor

Awesome, thank you.  Would it be possible to fill the base using mainly topsoil and then a few inches thick sand on top of that?  I'm trying to think of what would be the cheapest and easiest so I don't have to pay for a truck to deliver it.  I could just rent a Lowes truck like I did for the block.
« Last Edit: May 12, 2019, 11:18:33 PM by Pod4477 »

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Offline Jon in Albany

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #130 on: May 13, 2019, 07:21:48 AM »



b) mortaring concrete lintels to span across the blocks


Not sure what you mean by this. Are you talking about filling the top course of block?

Offline Jon in Albany

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #131 on: May 13, 2019, 07:30:50 AM »


Awesome, thank you.  Would it be possible to fill the base using mainly topsoil and then a few inches thick sand on top of that?  I'm trying to think of what would be the cheapest and easiest so I don't have to pay for a truck to deliver it.  I could just rent a Lowes truck like I did for the block.

I would assume that topsoil has some organic material that would eventually decompose and settle. If you are filling the stand, I'd go with well compacted and inorganic.

Also, you mentioned not being able to get the concrete formwork out if you cast a slab. You dont need to get it out. You can abandon it in there. Don't know how concrete compared cost wise to your other options.

Offline foreplease

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #132 on: May 13, 2019, 07:57:41 AM »

I would assume that topsoil has some organic material that would eventually decompose and settle. If you are filling the stand, I'd go with well compacted and inorganic.
I agree. Also, topsoil typically costs more than sand. Sand can get pricey if you demand only certain screen size(s). Fill sand can be very cheap but could contain anything from stones to organic materials such as clumps of grass to tree roots. There is not standard definition for topsoil or ďblack dirt.Ē It could turn out to contain anything shredded plastic garbage bags to partially composted diapers. Screened topsoil is a little better but will vary from place to place and year to year in terms of what percent of sand, silt, clay, and organic matter (and its source) it contains. It also has lots of weed seeds, which doesnít matter here. For many reasons sand is a better choice than topsoil.


Pod, I stand by my calculations in post 104 above. If you refigure it for the inside dimensions of your block work it will be very close IMO. Good luck.
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Offline Pod4477

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #133 on: May 13, 2019, 11:38:53 AM »

I would assume that topsoil has some organic material that would eventually decompose and settle. If you are filling the stand, I'd go with well compacted and inorganic.

Also, you mentioned not being able to get the concrete formwork out if you cast a slab. You dont need to get it out. You can abandon it in there. Don't know how concrete compared cost wise to your other options.

Sorry yup I meant for the inside of the block stand, and that was my thought of using topsoil or dirt from the yard.  Thank you, I didn't realize that, so the wood framing and hardibacker can be left in there?  I think that is definitely the cheapest option then. 

I agree. Also, topsoil typically costs more than sand. Sand can get pricey if you demand only certain screen size(s). Fill sand can be very cheap but could contain anything from stones to organic materials such as clumps of grass to tree roots. There is not standard definition for topsoil or “black dirt.” It could turn out to contain anything shredded plastic garbage bags to partially composted diapers. Screened topsoil is a little better but will vary from place to place and year to year in terms of what percent of sand, silt, clay, and organic matter (and its source) it contains. It also has lots of weed seeds, which doesn’t matter here. For many reasons sand is a better choice than topsoil.


Pod, I stand by my calculations in post 104 above. If you refigure it for the inside dimensions of your block work it will be very close IMO. Good luck.

I believe the local shop might have been talking about fill sand since it was so cheap.  He said $30 for around a ton to 1.5 ton.  Haha diapers don't seem fun, so sand definitely would be the better option. Thank you for doing the calculation for me.  I appreciate all the help with calculations and tips.  I reconfigured the dimensions and figured I'd update. The sand would be filling an inside area of 15.25 sq ft. (46.875"x 46.875" inside area) with a height of 29-31".  Having the sand stop at a max height of 31" allows me to build up a bit with concrete or the block caps about 3.75" height.  I may not have been right with my dimensions last time, but it seems that it would be 39.41 cu ft for the entire area of sand to fill
=1.4596296 cu yds
=2.04 T
2.04T/0.7=2.9T

Your calculations are much appreciated and I'll just have to check compaction rate for the type of sand they use, I guess.
« Last Edit: May 13, 2019, 12:06:58 PM by Pod4477 »

Offline Jon in Albany

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #134 on: May 13, 2019, 11:55:37 AM »
Sorry yup I meant for the inside of the block stand, and that was my thought of using topsoil or dirt from the yard.  Thank you, I didn't realize that, so the wood framing and hardibacker can be left in there?  I think that is definitely the cheapest option then. 

I believe the local shop might have been talking about fill sand since it was so cheap.  He said $30 for around a ton to 1.5 ton.  Haha diapers don't seem fun, so sand definitely would be the better option. Thank you for doing the calculation for me.  I appreciate all the help with calculations and tips.  I reconfigured the dimensions and figured I'd update. The sand would be filling an inside area of 15.25 sq ft. (46.875"x 46.875" inside area) with a height of 29-31".  Having the sand stop at a max height of 31" allows me to build up a bit with concrete or the block caps about 3.75" height.  I may not have been right with my dimensions last time but it seems that it would be a cu ft of 20.18 for the entire sand.
Dirty secret about my oven build...I let the slab sit a few days before taking down the forms. Well, I didn't wet down or oil the plywood I used as the base support enough and it stuck to the slab. Like really stuck. Crowbar and hammer couldn't move it stuck. The following summer the plywood fell down. But I had used the oven regularly without a problem. So maybe eventually some of your form might fall down. But it will be falling into a concrete box no one will ever see.

With a good amount of insulation between the oven floor and the slab, I dont think the top face of the slab will ever see 100 degrees. I'd guess less than than that.

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Offline Pod4477

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #135 on: May 13, 2019, 12:04:09 PM »
Dirty secret about my oven build...I let the slab sit a few days before taking down the forms. Well, I didn't wet down or oil the plywood I used as the base support enough and it stuck to the slab. Like really stuck. Crowbar and hammer couldn't move it stuck. The following summer the plywood fell down. But I had used the oven regularly without a problem. So maybe eventually some of your form might fall down. But it will be falling into a concrete box no one will ever see.

With a good amount of insulation between the oven floor and the slab, I dont think the top face of the slab will ever see 100 degrees. I'd guess less than than that.

haha that is something that would happen to me and something I thought about for the side forms.  My plan is that if do wood supports, I would just pour the slab over the top of the block and not even use block caps.  This way the slab spans the entire stand and would be more structurally sound.  I would build form supports just like Forno Bravo has pictured, with 9 legs, and 5 top pieces of wood that the hardibacker or plywood rests on.  So that can all be left in and even if it falls down the slab should stay up?  I'd probably do 2-3" structural concrete slab with a 2-3" insulated slab, so I hope that would be enough to prevent heat from getting to the wood.
« Last Edit: May 13, 2019, 12:10:13 PM by Pod4477 »

Offline Jon in Albany

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #136 on: May 13, 2019, 12:09:08 PM »


So that can all be left in and even if it falls down the slab should stay up?

If you build a properly reinforced slab, it will stay up without the formwork once the concrete cures. If there was a opening in your stand, you would be removing the formwork to create storage space, right?

Offline Pod4477

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #137 on: May 13, 2019, 12:15:15 PM »

If you build a properly reinforced slab, it will stay up without the formwork once the concrete cures. If there was a opening in your stand, you would be removing the formwork to create storage space, right?

oh yup true!  I'm wondering what the best type of concrete to use for the structural, between the 4000psi and 5000.  The insulating seems like it should always be 6 part perlite mixed with 1 part Portland cement.  I should probably do 4" for both just to be sure of insulation and structure.

Also, just called another local supply shop and they said it would be $104 including delivery for 2 tons of concrete sand, which can be delivered tomorrow.  I'll have to decide.  It's going to rain so I'd have to cover it, I assume.  If I use sand, my idea would be to use it just as a filler and added support, since I'm thinking I would pour the slabs over the entire span of the block stand and not just the inside.  That way instead of having the slabs sit only in the middle 39 cu ft of the stand, if there are any issues with the sand not being compacted properly, the slab should stay supported from the block. 
« Last Edit: May 13, 2019, 12:35:54 PM by Pod4477 »

Offline Jon in Albany

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #138 on: May 13, 2019, 12:45:12 PM »
Again (broken record), you need to pick your design. If you go concrete slab you dont need the sand. If you go sand, you dont need the inner concrete formwork. I will say from reading your posts, I feel like you are more confident with filling the stand with stand. I could be wrong. It's your build. As Anthony Falco recently said in a video, "chase your rainbow."

But should you go with a slab, you do not need high strength concrete for this. If you are using premixed bags, regular quickcrete is all you need...and some rebar.

Offline Pod4477

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Re: Wanting to build a coal fired style outdoor pizza oven
« Reply #139 on: May 13, 2019, 03:53:44 PM »
Again (broken record), you need to pick your design. If you go concrete slab you dont need the sand. If you go sand, you dont need the inner concrete formwork. I will say from reading your posts, I feel like you are more confident with filling the stand with stand. I could be wrong. It's your build. As Anthony Falco recently said in a video, "chase your rainbow."

But should you go with a slab, you do not need high strength concrete for this. If you are using premixed bags, regular quickcrete is all you need...and some rebar.

You're right.  I definitely feel more confident with the sand since I haven't done wood work in a long time.  I don't mind doing slab framing, but it's just the structural wood I worry about.  My idea was just that the sand in the middle would provide extra support for the slab if I fill over the entire block, instead of just filling concrete over only the sand.  Filling concrete over the sand or gravel only, has always seemed a bit risky after reading it in the book.  I feel this way the slab at least can have support from the blocks.  It was a good recommendation from you early on, as it eliminates any need for block caps. 

I guess I'm using the sand in place of the wood supports and pouring the concrete slabs right over it.  The only thing is that if I don't fill the sand right to the top of the block, the first support slab would have an odd shape from going down a bit into the sand and then up on top of the block.  The stand is 30.75" tall and that is even shorter than the 2 tons of sand I calculated (31" calculation), so my plan will probably be to fill the stand entirely with sand up to the top of the block, and then just pour 3-4" rebar concrete support over the sand and the block, followed by 3-4" perlcrete, using a wooden frame.  Out of breath there a bit.

Thank you as I was wondering if 5000psi was needed or not.  I already have an extra bag of regular quickcrete.  The water amount listed on the bag definitely was pretty dry when I mixed it the other night.  Since water decreases strength, but being too dry isn't good either, I'm assuming being in the middle is best consistency for the support concrete?  The insulating layer usually suggests adding enough water for the perlite to clump up.

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