Finally getting to building WFO in Calgary, Canada

[shanxk8]

Stacked up my foundation the first time (& them 2nd & 3rd). I found that the nominal concrete block size (8" x 16") is not the actual size. Their actual size is about 3/8" smaller in both dimensions. Therefore my blocks need a gap to achieve the structure size I had originally designed. Guess what that means, unplanned work... putting mortar between my concrete blocks (vertical only)... boooo.

[david s]

The blocks are designed for mortar joints so that is why the gaps occur. Just plug them up with mortar later. Just making two concrete block piers instead of a U shape allows you to butt the blocks together with no gaps. It also allows free flow of air to keep the wood drier.

[shanxk8]

It's been a slow couple of weekends work, but structure is now ready to have the hearth framing built. Here's a few more pics, & you can see how structure relates to the patio.

One thing i'm still sourcing is the insulation board. The one place i've found with ceramic board, it is VERY expensive, but has mineral wool board. I'd read a few posts that mineral wool board is not great, but looking for confirmation and the rationale. Might have to figure out if i can get cheaper shipping of the FB board from this site.

[UtahBeehiver]

Mineral wool board does not have the compressive strength necessary to support the floor and dome, you need something in the range of 90-100 psi along good thermal conductivity value (K). If cost is an issue you can look at perlite or vemiculate/concrete mix 5 or 6 to one for base, 8-10 one for the dome but you might have to increase the thickness of the insulation.

[shanxk8]

I've already purchased my CF blanket but the CF board that I've found works out to $21/sq ft and was only 1" thick, so the math in my head made it seem rather expensive to get 3" thickness. Surprisingly even more than shipping from FB in the US to Canada.

My wife seems to have found a local Forno Bravo reseller here in Calgary, so when time permits, i will have to contact them to see if they can supply the FB board.

Perhaps i should investigate the perlite/vermiculite route too. How long would i need to wait between pouring hearth & insulating concrete? (hoping for less, not more steps with 7+ day waits)

[UtahBeehiver]

I used Distribution International for my CaSi board (Thermogold 12), they have branch called Crossroads C&! in Calgary which provides insulation for the oil and plant industry in Canada. It might be worth while giving them a call to save yourself shipping from the US.

[agrasyuk]

Shanx , vermiculite-concrete is light. I'd say 36-48 hours should be enough for structural slab to harden to hold the insulAting slab.

[shanxk8]

Funny enough, Crossroads C&I is the place i contacted already. I'll have to call them back to ask about CalSil board. Fellow i spoke with identified Duraboard (expensive option) and Mineral Wool board.

[UtahBeehiver]

Duraboard is a AlSi material which will work as well as CaSI which is not inexpensive either. With P or Vcrete, either hold quite a bit of water so even though it is structurally strong enough to lay floor bricks on you will need more than a couple days for the material to dry out. It will be hard or harder to remove the water once the brick floor and dome are in place. So if time is a critical factor then P or Vcrete may not be an option for you.

[shanxk8]

Duraboard is the expensive one (i think listed as HPS board on link below). If memory serves, I was told the Thermogold 12 was only available as slotted board (that folds to wrap around pipes).
The options i think i have available from Crossroads are here:
http://www.crossroadsci.com/Technica...ataSheets.aspx

I'm also waiting to hear back on cost from the local Forno Bravo reseller. we shall see, as i hope to use a board rather than P or Vcrete.

[shanxk8]

Looks like the ceramic board option is gonna be really pricey and I'm now leaning towards v-crete.
Time to reread the plans on what is needed for that route.
I guess I'll spend the extra drying time cutting more bricks in advance.

[UtahBeehiver]

5 or 6 to 1 verm/perl to cement is a good rule of thumb for hearth base (probably at least 4"). Are you enclosing the oven or is it an igloo? If an igloo a 8 to 1 ratio on the dome over the CF will help you with the shaping and base structure of the igloo. If enclosed, some people have poured dry verm/perl after the enclosure walls are up for additional insulation. Attached is K values of various ratios

[shanxk8]

Planning an igloo, so have the CF blanket already. I hadn't thought of using vcrete on top to help with the igloo shape. (I figured i'd do that with the stucco, but it makes more sense to even shape out with insulating material then stucco over that)
Thanks!

For the vcrete, do you need the metal mesh installed before the same way you would with stucco?

[david s]

I know the plans say to cover the blanket in mesh prior to doing a vermicrete layer, but as it's very time consuming I don't add any mesh there.. If your blanket surface looks pretty even you don't really need it. I like to make that vermicrete layer quite lean (10:1), just firm enough to act as a reasonable substrate to work the outer stucco layer against. You want the strength in the stucco, not in the insulation layer.

[shanxk8]

Finished with the hearth pouring this past weekend, with some much appreciated help from both dads & a family friend. (whom we owe pizza) Who'd have thought lugging around 2600 lb of concrete a few times would be reasonably enjoyable.
Now I have the curing time to finish my search for insulation. I may even have found a source for the Thermogold 12 that Utah suggested. If that plans out, I might begin laying bricks this weekend.
Here are the progress photos of the hearth poor and a test brick layout with my newly constructed IT tool.