Why not curved lentil as oven opening?

[KISS4me]

Thanks for double explaining - I get it fully now

[UtahBeehiver]

You leave the pvc sleeves in just knock out the thin 1/2" top portion of the concrete with rebar or a metal rod. You plug with pvc with some newspaper or such

[KISS4me]

Clarification appreciated. Now have hearth layers clear and will incorporate 2-3 weep holes in concrete using 1/2" pvc pipe. I take it you dont leave pvc pipe in, hence the use of rebar to knock out when concrete is fully cured.

[UtahBeehiver]

A member used cheap 1/2" pvc pipe, install just below surface of the top of the concrete hearth (say a 1/2") so he could screed the heath nice and flat. Then took a piece of rebar and from the bottom of the pvc and knocked out the thing piece of concrete. 2 or 3 should be good.

[UtahBeehiver]

Just to be clear on David's comments, it is a 5 to 1 ratio of either perlite or vemiculite for floor insulation (btw, they are not the same materials, just similar insulation values when mixed with portland) or a 50/50 blend of vermiculite and perlite. It typically requires twice the thickness of p/v crete to equal a CaSi board.

[KISS4me]

Weep holes. Good point. What diameter and how do you create - pvc or metal pipe? leave in or remove when near set?

[david s]

Cast some weep holes in the supporting slab when placing the mix in the form. This allows a pathway for steam to escape both during the water elimination phase as well as later if there’s water ingress from

[KISS4me]

Well I never. Until you said this after reading the forum I had assumed that perlite was just a different name for vermiculture! Will go with the 50:50 mix as you recommend. Great advice about the water and hence the advantage of Hebel base before verm+perl crete layer. I now have a plan to work towards. Thanks again.

[david s]

If you do all perlcrete rather than Hebel /perlcrete combo you’ll be using way more perlcrete which means way more water. The proportion is 3 L water for every 10L perlite. I’ve found a mixture of 50/50 vermiculite, perlite makes a better mix than either alone. You will probably use it for the over dome insulation anyhow. The vermiculite does not contain the irritating dust that perlite contains. Don’t be too misled thinking the perlite is better because it has higher insulation value. Once you add some cement to it the insulation value of perlcrete and vermicrete is identical.

[KISS4me]

Excellent information. Thanks David. My conclusion:
As a base I plan going with 90mm reo concrete and for the next 100mm - either pericrete or a combo of Hebel then pericrete. Then undercooking surface ceramic heat board (the one I was quoted on is 25mm thick and 1000 x 500 for $A35 a sheet) before the floor tiles.
Sound OK? Any comment on all pericrete vs Hebel then pericrete in the 'mid section'?

[david s]

1.
50 mm calsil board (usual thickness) over 75mm Hebel is adequate underfloor insulation.If your question relates to that compared to 50 mm loose perlite over the 75mm Hebel, then no, the loose perlite has higher insulation value than calsil board, however most builders prefer to have the underfloor insulation layer far more solid. Usually recommended is a 5:1perlcrete or vermicrete which has a poorer insulation value than calsil board.It’s big advantage is its price over calsil board. It’s disadvantage is correct water addition, mixing, placement and then water removal.It is normal to have your highest quality insulation beneath the cooking surface so floor tiles, calsil, Perlcrete, Hebel would be the normal order of layers.
2. Usually dry placement is sufficient.

[KISS4me]

Visited a pizza oven builder/supplier here in Adelaide (Traditional Brick Ovens) and pleased to see that I can source ceramic fire blanket, floor tiles and flue from them. Although they do kits, not redbrick dome that I have in mind, they use a very simple hearth structure - no perlite, but Hebel blocks (about 75mm or 3") then one layer of CalSil (or ceramic heat board) of 25mm thickness and 50mm floor tiles. Although I found a few useful forum threads about this I have a few questions:
1. Is CalSil over Hebel blocks adequate insulation compared to perlite?
2. Do you need to mortar or sand fill between Hebel and Concrete and Hebel and CalSil?

Any ideas/links appreciated.
Steve

PS: Hebel is a lightweight concrete construction block. Probably called something else in other places

[KISS4me]

Slow progress. Stand construction coming along as per the photos here

[KISS4me]

Thanks for explaining why you would go to the trouble to curve cut bricks. Wrapping wall and floor in insulation makes sense. Cant see ours getting enough use to justify floor replacement. Could always lay replacemnt bricks on top of base if that was the case anyway. Because the floor of my first build did not absorb enough heat a I simply laid better suited bricks on top and this does the job.
Lots of ways to skin a cat!

[Kvanbael]

Hi Kiss4me: the brick floor is cut to outer dome edge as to facilitate insulation afterwards. Preferably, you want to wrap floor edge and dome in one go.

some would even cut the brick floor to fit INSIDE the dome so that the floor can be replaced after years of heavy use. But that is a whole different story.