32" build in Calgary, AB - pompeii neapolitan

[IH123]

Because all concrete is somewhat porous you may want to consider adding a waterproofing additive to the concrete for the supporting slab, I use Xypex. Water wicking up from the base can find its way into the inner parts of the oven where it can become problematic and difficult to remove. This is highly weather dependent of course, but never allow sprinklers against the stand for this reason. Another solution to this problem is to paint a sealer over the top of the supporting slab, but I have no idea about its longevity or how a sealer would stand heat.
30 x 30 kg is a lot of hand mixing, have you compared readymix pricing? You should be able to pour the cores and slab top in one go.

1-moisture could go up or down and the more dams I put the more focused and damaging it would become, I think I will just leave it natural for now (no vapour barrier on top slab) and would have to protect the site from downpour, rain, snow, and ice melts- I will not manage gaseous level moisture. its my first build and as long as a risk is not of high impact I will ignore it for the sake of completing and hoping the solution can be made after a problem occurs (only for low impact risks)
2-I already have the 60 bags (4000psi) in my garage wrapped with vapour barrier above ground, I have bought used 4 cu ft drum concrete mixer. I did mix 28 25kg bags for my bottom slab (6000 psi with fibre) so 30 30kg 4000psi bags wont be different. I will pour the grouts first and then after a bit of cure the top slab (not both at same time, too risky for leaks and blow outs)

[IH123]

If not already in your plan, you may want to consider center supports on the sides. Strap and blocks are one option,

why? straps are better than stakes ? the only place I don't have stakes is the front however I have inserted 3" nail through bottom workform and into the edge so edge can't push out ( nail shear) , and to protect legs from slipping outwards I used small stakes for them. rear, and sides I can have as many stakes as needed. my worry about straps is the don't have enough tension at the middle of the lumber, and if I use very strong banding then the form could be twisted.

The picture shows cmu blocks dry stacked (or may be glued?), I had mine mortared with type s mortar and staggered pattern so only risk of leg/stud shifting is bowing under weight , I have more of them to compensate.

do you think its serious to have that support on the studs/legs? because if so I could just have a long lumber joining them together and then put another shorter set of stakes for them too

[Giovanni Rossi]

why? straps are better than stakes ?

It's all good. Staked bracing will work fine. I couldn't see the back and it doesn't look like you have the angle to stake and brace the front with that hard patio in the way. I just know that sometimes guys underestimate the horizontal force that thickness of concrete can exert on the form. I'm not honestly sure if the nails in the front will prevent the top of the board from flexing outward. Even if it does, would it be significant??

As far as strapping, as long as the blocks in the center of the boards of the form are proud of any other blocking, the pressure points will be on the corners and the center blocks. You obviously don't want to tighten the straps such that you're deforming the boards inward.

To answer your other questions. :

I drilled into my slab on grade and glued rebar into the holes. The CMUs are dry stacked round those rebar. I filled the cores with concrete to a level about 4" below the top of the CMUs. Then put a 90 on the rebar and those legs are tied to the rebar in the top slab. The concrete pour finished filling the CMUs and formed the slab.

It looks like you have plenty of vertical support for the overhang of your slab. I banded the supports on mine because I have a really awkward site and I was afraid I would kick one of them out as I worked the concrete. I wasn't concerned about the ones in the front under the cantilevered section because I felt there was so much weight there that those legs weren't going to budge.

Looking forward to the rest of your build.

[IH123]

Today's work: grouted all cores leaving about 2" on top without grout so the slab would cap on it when poured. used 3 gram fritz pack air entrain + 15 grams fritz pack set delay per 2 30kg ready mix bags (4000psi) and about 5.6 litres of water (more than minimum to keep grout fluid), I vibrated with the concrete vibrator too, installed the top slab rebar mat

[UtahBeehiver]

Serious steel in there.

[IH123]

small change in the plan, instead of PVC pipe cut, I cut the rebars at corners so when corner is trimmed they wont be closer to it than 2", I use plywood pad to dampen the corner edge and when slab is cured I will use angle grinder or concrete saw to trim it proper a tiny. my next step is the pour of the slab, will be using 6 hours of set delay: for 2 30kg 4000psi ready mix, I will use 3gr of air entrain, 45 gr of set delay (all fritz pack) , and 20 grams of 1" poly fibers. I will vibrate with my 35mm concrete vibrator. next update is after top slab is poured and finished. have 34 bags to mix and doing it all by myself in the morning

[IH123]

The arch plywood forms

[IH123]

just finished the pour around 12:30pm, 2 hours ago, likely have to wait few hours before finish as 6 hours set delay makes it soft still

[david s]

Weep holes cast into the slab?

[IH123]

I am not going to create weep holes, I can wait as long as it takes for the slab to dry, same for perclite layer, here in Calgary humidity is always low except when there is downpour. its more important for me to keep the slab moist for at least 28 days so it can resist harsh winter frost heave and cracking, I have to design the oven to shed its moisture not through holes in slab, may be sideways

[david s]

I am not going to create weep holes, I can wait as long as it takes for the slab to dry, same for perclite layer, here in Calgary humidity is always low except when there is downpour. its more important for me to keep the slab moist for at least 28 days so it can resist harsh winter frost heave and cracking, I have to design the oven to shed its moisture not through holes in slab, may be sideways

Ok. 28 days damp curing is the industry standard, so yes, take your time and keep it covered for that long. If you are pouring your own vermicrete slab, be aware that there is a very large volume of water required in the mix, much of it is left as free water after the hydration process has chemically taken up what it requires, so extended drying is important before building over it and locking it in. Take a read of my attached experiment on drying a vermicrete slab.

Vermicrete insulating slab copy.doc.zip

[UtahBeehiver]

Take Dave's advice seriously. One of the most common reason an oven performs poorly is due to wet insulation, either left over from the build, IE pcrete mix, or water ingressing in and getting the insulation wet (water will find a way in). A way for water to egress has proven to be an insurance policy for us builders.

[IH123]

ok, david s and UtahBeehiver , I apologize if I appear to have taken this lightly and thank you for pointing this out. my slab workform had accidental 1-2 degree slop forward (front lower than back) and while I sprayed the slab with water this morning I could see the water has tendency to flow forward not backward. This would point out to potential hole location, front. Yes, burning fuel (gas, wood) will generate water vapour as part of combustion and release any water content from wood into air, water will eventually accumulate between cycles and with no guaranteed rate of evaporation in a well sealed oven , the risk of water pooling is possible. however, creating one or two 1/2" holes in slab can only be useful if water can be directed to that hole, for that to happen a porcelain mosaic tile with gaps between need to be placed under the insulation to allow water to flow ; however over time, and heat cycle expanding, contraction, settling: likely those gaps will become not useful because if they were tiny they will be filled with top layer creeping down on from moisture and if they are large gaps then creeping can be even bigger to distort any channels between the tiles. with most moisture is supposed to come from the hearth, not dome walls, and with hearth bricks are not supposed to have any refractory mortar on sides, vapour can go in and also out through chimney and oven mouth , however that will require slow heating and likely each time because no one knows how much moisture is pooling down. I also see it that to have the hole system work, with mosaic tiles, the insulation layer like perlite must be poured on a form and then transferred over the tiles because if pouerd over tiles directly then the cement will coat the gaps and close them, introducing cracking from moving a brittle layer of perclite. yes, building the oven will require a lot of unwanted water , that will be treated by slow curing. for instance, I have a 500000btu propane tiger torch, if needed , I can use it at lowest setting to warm the oven or even better place electric space heater outside at oven mouth blowing inside followed by bigger and bigger fires. I can close the door and place humidity meter in it when cool to tell how moist it is. therefore, treat the building water by curing. for water occurs by combustion, it should go from the chimney as hot gas and evaporation. I just find the simplicity of the design that everything enters from mouth and leave from mouth or chimney is the best, including vapour and water.

Can you tell me please why I should be worried about water pooling after curing? does burning wood produce too much water and does that requires the complicated capillary tile channels to transport that water down ?

I am not sure its worth it, I never seen a single video online doing this, can you please show me who did that?

[IH123]

Ok. 28 days damp curing is the industry standard, so yes, take your time and keep it covered for that long. If you are pouring your own vermicrete slab, be aware that there is a very large volume of water required in the mix, much of it is left as free water after the hydration process has chemically taken up what it requires, so extended drying is important before building over it and locking it in. Take a read of my attached experiment on drying a vermicrete slab.

[ATTACH]n471431[/ATTACH]

I already have 3 bags of perlite, 100 litres each, I plan to use perlite - cement, not vermicrete , while my 2" ceramic fibre board that I have is enough, I will still put a layer of perclite to have the concrete slab stays below 40c, even if oven is fired at 1000F inside. keeping the top concrete slab (6") cool , should help reduce effect of any pooled water I guess, as water wont be warmed enough to steam out and could safely dissipate in concrete while falling downwards and out

[david s]

Placing a dry calsil board over the tiles simplifies the need to eliminate water after the build. Casting a vermicrete or perlcrete layer over the tiles requires a layer of weed mat or similar material to hold the lightweight mix away from the channels between the tiles. It is the pressure increase from expanding air or steam as it is heated that forces steam out the bottom.through the channels between the tiles and out the weep holes. If this moisture is locked into the oven, it simply recompenses back to water only to be reconverted to steam the next time the oven is fired, this is what makes its early removal before building over it such a good idea. Sun and wind, if available for drying is the simplest. Fire internally then needs to be done slowly to avoid damage from expanding steam and or huge temperature differences which also mean huge thermal expansion differences between different parts of the oven. This is why it is also important when doing the drying fires, to allow the whole oven to return to an even ambient temperature allowing those hotter parts to contract and allowing some moisture to migrate back to the parts already dried, before the subsequent fire is started. Any moisture contained in wood exits out the flue, but a good proportion of the energy in damp wood goes towards turning that water into steam. Not too many oven owners fire with damp wood.