42” Massachusetts igloo questions

[djginivisian]

Hello,
Things have gone reasonably well to this point. I am ready to begin the insulation blanket. Likely 4 inches followed by “vermicrete ? , before being finished with 1 1/2 -2” thick stone veneer.

Oven is sitting on 2 inch CFB on top of 3 inch foam glass set upon a 7 1/2 inch cantilevered “countertop”. I have sourced materials from many places. Instrumental were the tapered bricks used for the base and every other course for the dome and archways . I used ceramic fiber rope as a heat stop between the outer arch, landing and events section

My intention is to encircle the dome perimeter with the 3” thick orange arc Bricks which the blanket and finish covering will “rest“ on.

My greatest question/ Concern is this; do I need to insulate the outside arches/chimney?

My secondary questions are;
Do I need to fill-in/smooth the gaps/surface around the dome before the blanket?
What type of mortar and waterproofing materials are recommended for the finish stone I will be using?

I intend/expect to do the initial firing/during after the insulation blanket. Is there a good link for a firing schedule?
Also, is chicken wire a no-no for securing fire blanket?

I appreciate any information and opinions. Also if there are other concerns, please advise.

-David G

[david s]

I’ll have a crack at answering, but no doubt there will be other opinions.But first my query for you is why the extra row of bricks outside the base of the dome? You really need to encapsulate the whole dome with insulation and as the base of the dome is the last place to heat up adding more thermal mass in that place seems counterproductive.
Now your questions, having insulated both under and over the oven very well and the entry/ flue gallery acting as a heat sink, it is probably a good idea to insulate it fairly well too. The tiny gap separating the gallery from the dome will work well as an expansion joint but not so good in preventing heat transfer. You wouldn’t expect the dome insulation of an equivalent thickness to prevent much heat loss. Even if you use half the insulation thickness of the dome over the gallery it will also protect it from the potentially damaging big temperature differential of an uninsulated gallery.
Regarding the parking of the inner dome surface before blanket application, I wouldn’t bother as the blanket will conform to a roughish surface. Maybe a rough scrape of the high spots with your trowel first.
There are many sealers for stone which will both waterproof it and enhance the look of the surface. I’ve found the best ones are those that are thinners based. Look for concrete or stone paving sealers.
For curing fires (I prefer to call them drying fires as curing often gets confused with damp curing where you are trying to keep the water in, just the opposite of the drying fires) See curing under Oven Management, firing your oven. https://community.fornobravo.com/for...curing#post833
read the whole thread. IMO it’s best to do the drying fires after insulation but before the final outer coating.

Most people cover the blanket with chicken wire to hold it in place. I don’t because it’s so time consuming. I build the vermicrete layer straight on to the blanket surface. This evens out all the uneven lumps and bumps of the blanket and dries to a firm enough substrate to work against for the final layer, in your case stone.

[mongota]

All of the following is simply my opinion.

I don't think it a mandatory requirement to insulate the vent arch, but I do think it can help with overall performance and longevity of the structure.

I used 4" of blanket over the dome and I was going to do 4" over the vent arch, but stopped at 2" on the vent arch.

After installing the four inch-thick layers of blanket, my dome blanket insulation as a whole was was firm, smooth, and stayed in place without moving. If doing vermicrete, I don't see a need for chicken wire. I used stucco, so I did use expanded stucco lath over the insulation and applied a couple coats of stucco to that.

I would recommend you use homebrew mortar over the outside of the dome to fill the voids. You seem to have some significant ones there. For me, that would be mandatory. That way you'll have a consistent thickness of firebrick/mortar across the entire dome.