Mongo's 42" CT Build

[mongota]

Thanks.

I have it covered with a concrete curing blanket. It's a burlap and poly blanket. Not perfect, as the blanket doesn't conform perfectly well to the compound curves of the dome shape. But it helps hold the moisture in. when I pull the blanket off to re-wet the dome, it's still a bit damp.

[david s]

Misting the surface thenconcrete strength on curing letting it dry again is not actually a good way to cure it. Concrete really requires constant humidity or wetting for the curing to work properly. Covering it with plastic is a better way to hold the moisture in constantly. Having said that, they guys who render houses never cover their work or even wet it down and the stuff doesn’t fall off. You’ll be fine.

concrete strength on curing
https://www.quora.com/What-is-the-mi...ement-concrete

[mongota]

Only took one day of misting the stucco shell to encourage me to dig around in the basement so I could up-size from the 16oz hand-held spray bottle that I used while building the brick dome to the 2-1/2 gallon garden sprayer. lol

[mongota]

How long are you going to let the stucco cure before your next fire?

I'm giving the stucco a week, actually 8 days, of cure before I waterproof it with a couple coats of Thoroseal. I'll then give the Thoroseal a few days to cure/dry before I run another fire.

Over the course of the current 8-day cure, the shell is being misted down several times a day. If I was not doing Thoroseal, I'd not have a problem firing the oven after those 8 days. I'd start with a low fire and after a couple hours I'd check the stucco shell for excessive warmth, with the warmth indicating moisture. If the stucco remained fairly cool, then I'd have no problem running a hot fire.

One thing to note is that the stucco shell is not my finished exterior surface. If it was, I'd have probably done a 3-coat application. I'll be covering the stucco shell with a ~4" thick veneer of mortared stone. The stone, I have plenty of it from my property. I'm contemplating the idea of leaving a gap between the stone dome and the stucco dome so structurally and thermally they will be independent of one another, but...I think that will be unnecessary.

[ASPLM]

How long are you going to let the stucco cure before your next fire?

[mongota]

Mongo,

That is the best insulation job that I have seen. Great job!

Looks like a snow igloo under the hot summer sun. Lol

[MichaelPBoisvert]

Michael, I used roughly 3-1/4 rolls, the rolls were 8# density, 2' x 25', 50sqft per roll.

When it came time to calculate the amount of insulation needed I had a 21" interior radius dome, but that dome was sitting on top of a 4" thickness of board insulation and a 2-1/4" thick floor brick.

So to calculate the surface area of my dome, I used the vertical radius of my dome versus the horizontal radius. From the slab the dome is built on measuring vertical, I calculated the radius by adding 4" of board insulation + 2-1/4" floor brick thickness + 21" interior dome radius + 4-1/2" dome wall thickness + 2", with that 2" simply being a point 50% of the way through the thickness of the eventual blanket insulation. A total radius of 33-3/4", which gives a surface area of 50sqft.

I knew going in that the 50sqft number was a generous number, because my first layer was going to sit on top of the 4" of board insulation, plus there was the vent arch which took away from the surface area of the dome that I needed to cover. And my dome doesn't honestly have a 33-3/4" radius. Geometrically, it's less than that as it's more like a half-sphere sitting on a section of cylinder.

So I bought four boxes, a total of 200sqft, and used roughly 3-1/4 to 3-1/3 boxes. I used the wedge-shaped off-cuts from covering the dome to cover the vent arch. They all knit together quite well.

This is very healpful! thank you. Looking great BTW! Very clean.

[UtahBeehiver]

You are really making up for lost time.

[mongota]

Great job! You're a very fast worker.

It's been a good productive week, Joe. I'm glad to be back at it.

[mongota]

Second coat of stucco:

Used the same 3:1:1/2 mix as I did for the first coat.

I'll let this set up, then I'll mist it for several days as it cures under a poly/burlap curing blanket. My plan is to eventually coat it with Thoroseal for waterproofing and then cover the shell with a stone dome. I prefer the Thoroseal as it's a cement-based product. I'll be be gone for a few days so that'll give the shell about a week of curing before I do the Thoroseal.

Not much to do now except let the shell cure.

[Gulf]

Great job! You're a very fast worker.

[mongota]

Stucco coat #1:

This went on well. The nice thing about working over the hearth slab is that any dropped material could be scraped up and reapplied on the dome. Pretty much zero waste. After the coat was done, I forgot about combing it out to give some tooth for the second coat. By the time I did think about it, if I'd tried to comb it out I probably would have simply sheared it apart. So I did some half-hearted dimpling with the notched side of one of my trowels.

Where the dome meets the hearth, you can see the bright red ring of the RedGard I applied over both the tapcons and the 1/2" lath return. That was done prior to the stucco.

Nothing fancy with the stucco, a 3:1:1/2 mix. I used about 50 lbs of portland, one wheelbarrow load of mix gave enough to work it into the diamond mesh and fully encase the lath. I was shooting for about a 3/8" to 1/2" thick layer.

[mongota]

I found that galvanized hardware cloth was easier to fit to the compound curve. But, after seeing your insulation fitting, I don't believe that you will have a problem with either.

The lath, being an expanded diamond lath? I had considered stretching and shaping it prior to installation to get it to conform to the curve of the dome. But then I decided to stop thinking and just start working. I do think too much at times. lol

I do have hardware cloth, that would have been much easier to tie together. But for the stucco coats to follow, this time around I preferred the diamond lath.

[mongota]

The lath went on well, it was tied together with rebar wire ties.

The lath I used comes in roughly 2' by 8' long pieces. I used the edge of a table to bend a 1/2" 90-degree return along the 8' length of the lath. I stood the lath on that return and then wrapped it around the circumference of the dome. I ran Tapcons through the 1/2" return to secure the lath to the hearth slab. After securing, I had a little bit of RedGard left in the bucket from way back when, so I used RedGard to seal the Tapcons, to "paint" over the return of the lathe, and I brushed more on the hearth slab to extend the ring of RedGard waterproofing out from the lath another couple of inches.

With a cylinder of lath wrapped around the half-sphere of the dome, I used an angle grinder to vertically slice the lathe so it could conform to the curvature of the dome.

I used 6" rebar wire ties to stitch it all together.

Not shown in the photos, but I added a second layer of lathe on the lower part of the dome where the cut lath abuts and doesn't overlap. That should help minimize the potential for the stucco cracking in those areas.

In one of those really weird serendipitous moments, I had maybe 1-3/4 packs of 6" wire ties that I bought when I started building the oven. I used them up, and was going to have to run out to get more. I went in my basement and found the remnants of a REALLY old package of wire ties. They had to be 20 years old from when I built the house. There were maybe two dozen wire ties in that package, covered with surface rust, and that was exactly the number I needed to finish stitching together the lath.

Perfect.

And I have to say, the older ties were much better to use than the newer ties. The new ones would snap if you sneezed at them. The old rusty ones, I could snug them tight and not one snapped.

[mongota]

How many rolls of fiber blanket did you end up using? Are they 25' rolls?

Michael, I used roughly 3-1/4 rolls, the rolls were 8# density, 2' x 25', 50sqft per roll.

When it came time to calculate the amount of insulation needed I had a 21" interior radius dome, but that dome was sitting on top of a 4" thickness of board insulation and a 2-1/4" thick floor brick.

So to calculate the surface area of my dome, I used the vertical radius of my dome versus the horizontal radius. From the slab the dome is built on measuring vertical, I calculated the radius by adding 4" of board insulation + 2-1/4" floor brick thickness + 21" interior dome radius + 4-1/2" dome wall thickness + 2", with that 2" simply being a point 50% of the way through the thickness of the eventual blanket insulation. A total radius of 33-3/4", which gives a surface area of 50sqft.

I knew going in that the 50sqft number was a generous number, because my first layer was going to sit on top of the 4" of board insulation, plus there was the vent arch which took away from the surface area of the dome that I needed to cover. And my dome doesn't honestly have a 33-3/4" radius. Geometrically, it's less than that as it's more like a half-sphere sitting on a section of cylinder.

So I bought four boxes, a total of 200sqft, and used roughly 3-1/4 to 3-1/3 boxes. I used the wedge-shaped off-cuts from covering the dome to cover the vent arch. They all knit together quite well.