42" Corner Pompeii in Coastal Virginia

[Denamontini]

Jewels of wisdom on the cure? How long do we let it sit before the first mini fire?

Now I need the brain trust to give me a few ideas...
How shall we finish it? We like the stucco look and we want to keep the oven looking like a dome. What’s best practice in using stucco or a stucco-like product? We live in a mild climate with plenty of rain and humidity.
Any ideas? (Personally, I’d like to tile it with the tiny 1” mosaic tiles, but the Mr. seems to think that would take a long time.) My main concerns are creating a water proofish outer shell that will not crack.
Has anyone been successful without putting a roof on it?

Thanks again!
Dena

[CoastalPizza]

... We like the stucco look and we want to keep the oven looking like a dome. What’s best practice in using stucco or a stucco-like product? We live in a mild climate with plenty of rain and humidity. Any ideas?....

I also wanted to keep the dome shape so went with a stucco render coat followed by Seal-Crete waterproofing. If you isolate the outer dome from the inner oven with some sort of soft(ish) insulation, the inevitable thermal expansion of the oven's core is transmitted less to the stucco render. I went with about 3-4" of rockwool batting followed by 2-3" of perlcrete to act as a base for the stucco. Also, I used Quikwall rather than regular stucco for the base coat over the perlcrete since it is reinforced and fairly waterproof. I tinted the stucco finish coat with Ironoxx pigment. Since curing, I've done three full 900°F plus firings for pizza and no cracks so far.

[Chach]

Great Job!

[UtahBeehiver]

Congrats on plugging the dome. As far as curing, this is where a lot of builders get impatient and fire too hot, too fast. I would suggest you get the dome insulated before doing and firing, insulating the dome reduces the temperature difference between inside and outside the dome which reduces the chances of cracking your hard work. You could start some mild heating a halogen light, then briquettes for a few (you can cook some dutch oven stuff) then, then small kindling fires and so on. One extra log of the fire can really spike the temp. so again, be patient.

[Denamontini]

I also wanted to keep the dome shape so went with a stucco render coat followed by Seal-Crete waterproofing. If you isolate the outer dome from the inner oven with some sort of soft(ish) insulation, the inevitable thermal expansion of the oven's core is transmitted less to the stucco render. I went with about 3-4" of rockwool batting followed by 2-3" of perlcrete to act as a base for the stucco. Also, I used Quikwall rather than regular stucco for the base coat over the perlcrete since it is reinforced and fairly waterproof. I tinted the stucco finish coat with Ironoxx pigment. Since curing, I've done three full 900°F plus firings for pizza and no cracks so far.

Sorry for the delay! Thanks so much for the information! We are using a ceramic insulation blanket. Will that work the same as rockwool batting? What was your perlcrete mix/recipe? How long did it take to set up?

I went back to your builds and looked at how everyone attached the chimney. Did you have additional bricks covering the anchor plate one it was attached? My husband is convinced that the chimney system is too big and too heavy. Any thoughts? (it is 8" insulated, 36" tall stainless steel) Did anyone secure it beyond the anchor plate?

As always, THANKS for your time and wisdom!

Dena

[Denamontini]

What is the exact kind vermiculite/perlite that I need for over the ceramic blanket? It is not the garden variety, right? Can someone show me a pic of what they used and where they got it? I am very unsure of this part.

[CoastalPizza]

...We are using a ceramic insulation blanket. Will that work the same as rockwool batting? What was your perlcrete mix/recipe? How long did it take to set up?

I chose rockwool over ceramic blanket due to cost. I think the ceramic blanket is actually easier to work with and is a better insulator. Most folks use 1-2" of ceramic blanket while I ended up using about 3-4" of rockwool. Since the perlcrete isn't under any load, I went with a 1:5 mix (cementerlite by volume). I mixed the cement first, pre-wet the perlite (using a bucket with holes in the bottom), then mixed the two. About 5-6" is the maximum height you can apply when going up the side of the dome, otherwise it slumps. I did a layer a day so it took 3-4 days to get up the sides of my dome. The perlite I used is the same stuff you get at a garden center. Try to find a place that sells it in 2 cu. ft. bags - the small bags at the home stores is pricy. See post #9 in this link for a good description of mixing perlcrete: https://community.fornobravo.com/for...2-build?t=7155

I went back to your builds and looked at how everyone attached the chimney. Did you have additional bricks covering the anchor plate one it was attached? My husband is convinced that the chimney system is too big and too heavy. Any thoughts? (it is 8" insulated, 36" tall stainless steel) Did anyone secure it beyond the anchor plate?

I went with a clay flue liner covered in 1.5" of perlcrete and then covered in stucco to match my dome.

[Denamontini]

Thanks for the info! I will prob touch base again when I’m ready for that part. Dang, I’m rethinking this super expensive super heavy stainless steel chimney system...

Ok, the bad news... I jumped the gun taking the form off of my outer arch, yanked on it too hard 25 times and I cracked all of my work!?!

The good news... I was able to rebuild it all and fix the stuff I hated about it! My bricks were too far outward and I had over estimated how much room I needed for the chimney. So listen up, newbies, DON’T remove the arch forms too early with a sawing-like motion!!!! (Yes, I had it shimmed for the drop down method of removal, but got impatient ...)

[UtahBeehiver]

You can get construction grade perlite at any masonry supplies store, not your big box store but where the pros go to get concrete blocks (CMUs) the perlite is used to insulate block buildings by dry pouring into the cells of the block. This is probably the least expensive source for you. You can do up to a 10 to 1 ratio but at this it is a little hard to work with. With a CaSi blanket underneath, 5-8 to 1 will work fine. Attached is a chart showing the various K values at different ratios.

Actually, double wall insulated SS pipe is quite a bit lighter than a masonry/brick chimney. I have a four foot section on my oven and have not had any problems in 7 years.

Patience, grasshopper, is the wisdom of the day.

[UtahBeehiver]

[Denamontini]

Russell,

Thanks for the info. In the ratio, the first number 5-8 is the perlite, correct? And secondly, about how much am I looking for to buy? Just a ballpark figure, if I copied your technique.

Also, do you have your pipe secured at any other spot besides the anchor plate? Did you mortar bricks over top of it? It looks like you did not???

Thanks again!

[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.

[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.

[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...

[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.