Making a Vermiculite/portland 'shell' on top of Insblock-19? Experiences & advice :)

[Dazzlin]

Hey everyone,

So, as the title suggests, I'm having a little bit of a crisis on what I'd like to do, but is it feasible -- sort of thing...

Anyway, here's my dilemma... I've put a nice 4 1/2 inch thick slab to form my hearth and acquired some of this "Insblock 19" fibreboard stuff for my under-cooking-floor insulation... Now I've been reading multiples of that it's good stuff, and how it can withstand the weight of the oven being built on it (etc etc)... On the same note, I've been reading how if the stuff gets wet, being fibre board, it turns into a sort-of mush and becomes rigid again when it dries out...

This, for me, is concerning. Because I'm intending to (like most people) do a 'one time build', I'm having difficulties coming to terms that the insulation may become weak/move/break down in the fullness of time...

One idea I came up with, and this is where I need your help and experience(s), is to build a 3" 'frame' around the insblock layer (noting that the insblock is only 2" thick) and pour a layer of Vermiculite-portland mix to encase the insblock... thereby giving it a 'hardened, airtight, layer/shell' thing...

My worry concern was that the Vermiculite on top of the insblock would only be an inch thick and I am worried that this might also break down when the bricks are hot owing that it is a lot thinner than the recommended 3" layer that is usual where insblock/fibre board isn't used...

Does this kind of make sense to anyone...?

All experiences welcome. Thanks all.

[Laurentius]

Re: Making a Vermiculite/portland 'shell' on top of Insblock-19? Experiences & advice

Dazzlin,

You have the Bull by the tail rather than the horns. First of all the ceramic board will not turn to mush, it will absorb water if left in a situation where it can get wet. Secondly if you are going to use it in conjunction with vermiculite, it should sit on the vermiculite not encased in it. The vermiculite is a magnet for water and takes longer to dry, so try make you oven as waterproof as possible, the guideline from FB are as good as it get. Enjoy your project and feed your masses.

[dmun]

Re: Making a Vermiculite/portland 'shell' on top of Insblock-19? Experiences & advice

Insblock19 is not the product that breaks down if it gets wet. That said, you want to keep it dry as possible, because no insulation works well if it gets wet.

I'd steer clear of combining it with a thin layer of vermiculite concrete. I don't think it serves any purpose. If for some reason you want more than the two inches, add more board. It comes in different thicknesses.

[GianniFocaccia]

Re: Making a Vermiculite/portland 'shell' on top of Insblock-19? Experiences & advice

is to build a 3" 'frame' around the insblock layer (noting that the insblock is only 2" thick) and pour a layer of Vermiculite-portland mix to encase the insblock...

I understand your concern. My solution was to surround my Insblock with my support slab thereby protecting it and the vermiculite layer below.

We all contend with trying to keep our builds dry during inclement weather. Some build under existing structures, most, like me, use a tarp or pop-up.

[Dazzlin]

Re: Making a Vermiculite/portland 'shell' on top of Insblock-19? Experiences & advice

Thanks for the empathy guys --- having read your responses, I'm quietly confident and prepared to proceed without any sort of encasement...yet... Perhaps, once the dome is built, I should just focus on putting on the optional 2" layer of morter as thermal mass and just bring that all the way down to the slab level to encase the insblock/oven completely...

So I've just drawn up my 'battle lines' on the insblock and am prepping to go out and get some firebricks to start building the oven floor... Having seen some other peoples pictures I'm actually rather worried - as there is a lot of good work out there to contend with...

[GianniFocaccia]

Re: Making a Vermiculite/portland 'shell' on top of Insblock-19? Experiences & advice

Think of your final enclosure (either roofed 'house' style or igloo) as the means to encase your oven and insulation. No need to do it any earlier. If you run 2" of extra-mass mortar down to slab level you will cause your oven to bleed heat away into the slab. I'd vote against it.

[Dazzlin]

Re: Making a Vermiculite/portland 'shell' on top of Insblock-19? Experiences & advice

Again, good advice received... Thanks

[Laurentius]

Re: Making a Vermiculite/portland 'shell' on top of Insblock-19? Experiences & advice

Hi Dazzlin,

I did as you suggested, I also wrapped a strip of ceramic blanket down to slab level before adding the mortar, to act as a buffer zone, so that hear wouldn't drain into my slab.