39 inch Corner Build

[JRPizza]

I have a question for DavidS, and will post it on my thread so as to not hijack LarryP's any further.
I had not considered applying the p/v-crete directly to my insulation - I"ll see how even I can get it without any mesh over it. My question is in regards to how much perlite and vermiculite I might need to cover my oven. I have a 39" dome that I plan on using 3" of insulation over. If you usually put down 35mm, could you give me an oven diameter and approximately how much product you are going through? Anybody else that wants to pitch in please do.
I also forgot to ask - you said add a handful of clay - fireclay?

[UtahBeehiver]

I believe David's rule of thumb is calculated volume based on thickness plus 20% but check with him for sure. I also had 3" CF then added 2-3" of P-crete plus also rendered with 3/4" of stucco for a solid base for the copper shingles.
Re: perlite

Originally posted by gaetanin View Post
thanks for that, will give it a go and see how I get on. Would you advise just 1 coat or more I have a 100 ltr bag of it so have lots I can use.



you don't say how big your oven is, or whether you are relying on perlite as your only insulation material. Are you using a CF blanket under the perlite too?
4/3 x pi x r x r x r = volume of a sphere. Work out outside volume and subtract inside volume then divide by two because it's a hemisphere. Also add 20% because perlite volume will be reduced on mixing with cement and water.I like to do the layer about an inch and a half thick, then let it dry for a week before adding the next layer and so on. This way you can eliminate the water more easily later.

Last edited by david s; 08-02-2013, 11:51 PM.

[JRPizza]

Thanks Russell, that makes sense. Just presume that a cubic foot of dry mix will give about .8 ft^3 of wet mix allowing for some compaction of the vermiculite and perlite. A quick calculation says I need about 3.5 cubic feet of dry p/v for the first inch of cover.
You mentioned putting stucco over your p/v mix, did you feel the stucco was needed as the p/v-crete was not structurally sufficient on its own, did you think it was a superior substrate to mechanically fasten to, or was there another reason? I'm planning on adhering tile/rock/brick (still tbd) so I want my layer(s) to sufficient but not overkill. I'll probably use some kind of wire over my insulation, as I want to get it on sooner rather than later, and don't want to have to fetch it from around my yard after a good wind like I read about in some builders post.

[UtahBeehiver]

JR,

I needed to fasten the shingles using clips and 1" SS self tapping screws. The P/V crete did not give the screws enough to bite into and hold so hence the stucco. You need to talk to Gulf about whether P/Vcrete alone is good enough for brick or tile substrate, since he did brick tiles on his build. Gulf rendered his P/V crete as well but get his take on it. He also used 1/2" welded mesh under his P/Vcrete.

[david s]

I have a question for DavidS, and will post it on my thread so as to not hijack LarryP's any further.
I had not considered applying the p/v-crete directly to my insulation - I"ll see how even I can get it without any mesh over it. My question is in regards to how much perlite and vermiculite I might need to cover my oven. I have a 39" dome that I plan on using 3" of insulation over. If you usually put down 35mm, could you give me an oven diameter and approximately how much product you are going through? Anybody else that wants to pitch in please do.
I also forgot to ask - you said add a handful of clay - fireclay?

Yes, you lose around 20% of the volume, maybe even more because you will drop a fair bit of it when you apply it, it's pretty messy stuff. Just calculate the volume using final diameter minus diameter of insulation. Divide by 2 cause it's a hemispher. What you don't need because of the oven mouth is taken up by the extra required around the flue.
Regarding clay, any will do, whatever you've got, ball clay, kaolin, bricklayers clay, fire clay etc. added in a powdered form is the easiest way for best distribution in the mix, but I guess you could use slip too.

[JRPizza]

I have a pretty healthy heat break between my vent arch / flue and my inner arch. Is insulation really needed on the vent arch if it is not in direct contact with the dome? I've been thinking of maybe just going with the firebrick look - not sure, but if I do was not planning on insulating the flue arch.

[Gulf]

JR,

In my opinion, the stucco layer is "very much" necessary for attaching a stone or brick veneer. V/Pcrete, alone, will not have a "secure enough grab" for the thinset to adhere.

Having enough insulation already with the ceramic fiber blanket, I consider the v/pcrete thickness only as a means to true up the circumference of the sphere. The thickness of my vcrete layer was any where from 2.5" to 5.5" thick to accomplish this. That is because I had a very lumpy dome insulation application. Had, I of had the Forno Bravo How to insulate, Shape and lath your dome Video under my belt, I would have had a much more efficient application. Check all the Forno bravo videos out before you start. The stucco videos are good stuff also.

If I had it to do again, I still don't think that I would skip the vcrete. But, had I of used the FB method of applying insulation, I would have been able to use a lot less vcrete for the shell, and would have had a lot less drying time.

If you do use the v/pcrete to get to a perfect shape, the chicken wire , applied next to the ceramic fiber insulation, is thought to keep the v/pcrete from compressing the insulation.

[JRPizza]

Thanks, I'll check out the video's. I did my 6th and 7th curing fires. On 5 & 6 the dome partially cleared. I "cooked" some cinnamon rolls that my wife made, and they were burned on the top and smoky. Sure I could have read that you need to remove all the coals so you don't make your baked goods taste like railroad tie, but it's way better to learn on your own.
I decided to crank it up on my 7th fire and cleared the dome. If you look careful you can see the crack that developed running up the back side. Again, I saw that it is better to insulate first before going for the really big fires, but it didn't fit my schedule. I don't know if the cracks would have been smaller/lesser if I had insulated first, but oven's crack, right? At Boeing we used to say that an airplane is a collection of parts flying in close proximity. I think the same of an oven - a collection of bricks, expanding and contracting in close proximity. I also was planning my Sunday bread bake and figured I might as well try out the oven as it "seemed" to be hot enough. Without insulation the dome didn't stay hot enough to really brown the tops, but I was really impressed with the oven spring I got and think I got some valuable experience from both my cooking attempts. I think it was DavidS that said if it is too hot, protect the food, and if it is too cool, cook it longer. Cooking bread in my oven is going to be much easier than I thought it was going to be.

[JRPizza]

I'm in a holding pattern waiting for the wind/rain to die down so I can work on my insulation and roof, so today I mortared in the chimney cap bricks. They hide the adapter plate and give the chimney a finished look. I think/hope I am done cutting firebrick unless something cracks, so I can put my saw away for a while

[deejayoh]

That bread looks pretty good for a first attempt! I always find for a couple loaves - the dutch oven trick is hard to beat. Don't usually fire up the WFO unless I have about 10 pounds of dough

[JRPizza]

Yes, I bake bread in the house oven once a week, and have been using the covered pot method for the last few years with good results (see pic)
I'm hoping however to get into a rhythm with my WFO of cooking pizza, then bread, then slow cooking every weekend.
BTW, I have a starter I have been feeding for over 25 years, and have no idea how old it was when I got some of it from a friend. If you want I'll bring you some when I finally get over to see your oven.

[deejayoh]

OK, that splains things. You've been at this for a while! Love to have some starter. I have one - but it's interesting to compare. Trade you some Ginger beer mother.

[UtahBeehiver]

JR,

That is my next quest is to bake bread like the ones you did in the dutch oven. My attempts so far have only been barely edible and really ugly.

BTW, nice little brick accents on the side of you chimney, looks like you are golden on the brick cap.

[UtahBeehiver]

DJ,

You and JR figure out which of the sour dough starter works best in a WFO and pass some on to your old Utah buddy.

[JRPizza]

Russell, I'll send you some anytime! Do you have a starter you are using now or are you using commercial yeast?