42" Corner Pompeii in Coastal Virginia

[SableSprings]

Dena, 2" of ceramic batting is good although many would say to add some more because you can't over insulate. By using chicken wire and perlcrete/vermicrete over the insulation blanket, you are simply adding more insulation AND providing a more solid substrate for your final render/stucco on the outside.

Note that David S has gone to adding fibers to his outer render to help it stand alone (without a chicken wire base over the blanket). I still like the 8:1 or 10:1 insulating concrete (with some added clay for workability) over chicken wire that's holding the batting in place. Primarily because you can shape and smooth the dome exactly how you'd like it before adding the final waterproofing render/stucco layers. This is also my favorite method because you are securing the insulation batting in place during the curing process which may take a week or more. Then, when the last outer render layers are put in place, you are not having to deal with moisture still trying to escape through it and causing "cosmetic" problems...

[Denamontini]

Cory,
WOW!!! That looks/looked great!!! I’m reconsidering. I may hold off on the insulation until I get a little farther on the build. I still need to get the on chimney and complete the decorative arch. Did you put the stucco render straight on the insulation covered in chicken wire? It looks so smooth!

Russell,
I bought the 2” insulation blanket that you had posted about. (The good deal you had snagged a few rolls of... but I paid $100/roll) Anyhow, in your opinion, will the 2” insulation blanket be sufficient or should I also add the cement/vermiculite/perlite render. I was prepared to do it, but it is redundant?

Thanks again for all of the help!
Dena

[UtahBeehiver]

Just like Cory said. Cut like orange wedges. Save the scrapes for your door.

[cbailey]

It depends whether you are going for an igloo or enclosed. I opted for an igloo. My goal was to make the blanket layers as smooth as possible to facilitate a smooth render/stucco layer.

The stuff cuts pretty easily with a utility knife, and generally holds its shape. It's nasty stuff, so wear goggles, mask and long sleeves. I cut mine in wedges as you mention. The goal was to get a first layer with tight seams rather than over laps. Do the same with the second layer while staggering the seams, and perhaps a third layer. I covered mine with 3 layers of 1 inch blanket.

I finished the decorative arch on my oven before rendering the dome. The deco arch extends 2.5 inches beyond the firebrick outer arch. That provides a nice channel for snug fit for the blanket. The render forms a nice seal against the deco arch providing better insulation, and optimum protection of the insulation from water.

Cory

[Denamontini]

I’m thinking I’ll just take wedges out an make it smooth?

[Denamontini]

What?!? This insulation blanket does not come shaped like a dome? I’m kidding. How precise do I have to be shaping it? This seems like a nightmare... any tips?

[Denamontini]

Happy Tuesday everyone! Here’s my progress. I fixed the outer arch and it’s solid! We’ve been doing some small curing fires with paper and small pieces of wood. We are going to put the insulation blankets on before we go any hotter. Still need to construct the chimney support.

[Denamontini]

Update... I ran home after work determined to rip it all down and start again. When I got home, the mortar lines looked different and fuller. Still, I went at the mortar joint with an angle grinder and the keystone brick really was solidly stuck. I picked off the loose debris re-mortared where I grinded away. Then I cut and mortared in an identical keystone right behind the first one to provide more support. We are supposed to get a few days of rain, so I guess I’ll just wait it out and re-test it once the weather clears up.
I’m sure career masons cringe while reading posts like this. Sorry!

[MickyPizza]

I would redo it. Totally, no question. If you think THAT'S a ballache, It took me FOUR attempts to get an arch that I was either happy with or strong enough!

I did similar and that face on brick wasnt strong enough. I did two face to face and next day the oven side one simply fell out. There could be a lot of stresses pushing out against that brick. It looks a similar set up to how I did my vent etc. I wasn't happy about whether or not those long, vent siding bricks would hold for, so I mortared in some small cut firebricks between them and the dome for extra rigidity. Personally I would do a half brick there with hammered in brick wedges, like my pics 3 and 4.. That arch was one of the biggest problems I had. Difficult when you're making it up as you go along isnt it! good luck

EDIT - NOT like mine at all, this is actually your OUTER arch... Im tired!! haha

[Denamontini]

[Denamontini]

Shoot, I have another issue that needs to be voted on by the smart people reading this forum.


This is my outer arch (that will get covered up with decorative brick) I have no masonry training, so I made up a solution to having too much space, but not enough space and I turned a full sized brick sideways and angled it to made a keystone. It is only 2.25 inches deep. The clearance on the back was helpful in providing space for the chimney. There are hailing cracks on both sides of the keystone, (no where else) but it doesn't not budge when I yanked on it. (It was set about 18 hours ago)

Should I
1. Keep it as it is. Let it set for a few more days and just live with it.
2. Keep it and re-set it in new homebrew and reinforce the back with something.
3. Redesign the keystone spot all together.
4. do something else

Pics in the next post since they are on my phone and I am using a computer...

[david s]

The most important thing is to get the correct amount of water in the mix. Too little makes the stuff more crumbly to apply, too much and it washes the cement off the grains. I’ve found 3 litres of water for every 10 litres of perlite or vermiculite is about right, but the finer the grade the more water is required. I also find a 50/50 mix of vermiculite/perlite works better than either of them alone. Also found mixing dry materials in the barrow first, then folding in a third of the water and knocking down any lumps that form with the back of the spade, then add second third of water, repeat procedure and finally same with the last third, will give you a good mix. Should you end up with water pooling in the bottom of the barrow add a bit more dry material in the same proportions to suck it up. Mix gently to avoid abrading and degrading the aggregate grains. The volume of the mix will reduce about 20% when you add water and mix it, so this extra volume needs to be also accounted for.

[SableSprings]

Russell,

Thanks for the info. In the ratio, the first number 5-8 is the perlite, correct?

Yes Dena, the larger number is the perlite. So 5-8 parts perlite to 1 part Portland cement (not the mix with gravel and sand ). These are by volume, so just to check batch size, find a bucket and assuming you will be doing a 7:1 mix, put 8 buckets of dry perlite in your wheelbarrow just to check that it is going to fit and you'll be able to mix it easily with a shovel. When you're happy that you've either got a bucket of the right size (or have marked the bucket), then you'll do the 7 buckets of perlite and 1 bucket of Portland. Also, David S has noted in previous threads that if you throw in a handful of fireclay with each batch you mix, it makes the perlcrete (or vermicrete) easier to work. The reason you are mixing slowly (with a shovel) is that you don't want the perlite to break into smaller pieces (which would happen with the more vigorous action provided by a cement mixer).

I attached a couple pictures from a 10:1 perlcrete mix for my dome (since the ceramic blanket was even more expensive in 2009 ). Note that you can see where I added water to the cement/perlite dry mix and the cement just "washed off". I added water slowly and mixed from the bottom, when you have enough water you should be able to easily form a "snowball". I think if I would have known David's fireclay addition trick it would have been a lot easier.

Be aware that you are going to find getting the perlcrete to stay on the more vertical area to be a bit of a challenge...again the clay and having a base like chicken wire or metal lath secured over your ceramic batting can be helpful in providing a little base for the perlcrete to attach. You may also find using some bender board to make a temporary form around the dome perimeter for application of the crumbly perlcrete is helpful. Hope this helps...

[JRPizza]

My anchor plate sits bolted to a layer of bricks, with a decorative "crown" around it that theoretically would allow me to unbolt and remove the plate if I ever needed to. My pipe goes up through my roof and gets additional support from the silicone boot/flashing that keeps the water out. We have two 3' sections of pipe with a cap on top.

[UtahBeehiver]

Yes. I used 2 - 4cu ft bags, abt 10 bucks a bag ib 2012. There is a layer a brick on top of anchor plate, it shows in my pic log.