39 inch Corner Build

[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]

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?

[JRPizza]

Yeah, I'm checking with the county. I think code is 2 feet above the nearest roof line within 10 feet, which in my case is the structure roof. I have an extra 3' of supervent I got free cause it was dented, but want to keep the pipe as short as possible. I'm out in the sticks and don't need a permit for my structure, but exempted structures are supposed to comply with code nonetheless.

[RandyJ]

Hi there Jr I have one question for you. What is the roof going to be on your roof there? The top of your chimney looks kinda low in comparison. I know code is different from place to place, but wee need to be 3' above the top of the closet roof line.

Randy

[JRPizza]

Got done with my 5th curing fire. First picture is evening after the 4th and I'm still pushing out water. Before I lit my 5th I test fit the chimney vent pipe. The 5th fire got locally hot enough to partial clear the dome. The base was dry but later when I checked it was starting to leak again. Cooked some brats with the coals ;-).

[Larry P]

If you have trapped water it'll either come out like mine did or as steam if you get it that hot. Did you start your burn this weekend as planned? I'm on my fourth burn and the water keeps coming...

First burn today. It's been going for about 6 hours now. I've been Pretty good holding the dome under 350, but it has gotten up near 400 a couple times.

[david s]

If you see steam, back off, you're going at it too hard and you risk damage.

[JRPizza]

If you have trapped water it'll either come out like mine did or as steam if you get it that hot. Did you start your burn this weekend as planned? I'm on my fourth burn and the water keeps coming...

[Larry P]

Wow! Would not have expected that. It will be interesting to see if mine does the same thing.

[JRPizza]

I thought it might help folks understand. Here is one more "morning after" shot of how much water came out last night after we shut down for the evening. I tried to add the shot to my previous post but the forum is being kind of wonky.

[RandyJ]

I am glad you caught that. It is a good lesson for all future builders. It shows that there really is a good reason that you need to do the curing fires in the proper way. Good luck with the rest of the curing process.

Randy

[JRPizza]

This is why we cure low and slow. My first two fires I kept the dome around 300-350, Today I was shooting for 400-450. Started the fire early and after about 6 hours I noticed water coming out from under the CF board on one side of the oven. Second pic is from a few hours later and the water is still being pushed out. My first course of bricks is around 220F. I'll keep going at this size of fire for the rest of the day/night, then do the same tomorrow (and beyond) as long as water is still appearing. When I don't see any more coming out I'll go for 500-550 at the top of the dome. .
The oven has been covered since last fall except for dry days where I uncovered to allow moisture out. This water is probably what got trapped late last summer when it got dumped on with only a few courses mortared in. I hate to think what might have happened if the first fire had been a big one - thanks to the forum for the curing advice!

[Larry P]

All good suggestions JR, thanks. If it's raining I guess that will keep the canopy cool but yeah I think I don't need to worry about draw too much, and also don't care about smoke-staining the ebony bricks on my outer arch either.

[JRPizza]

If you saw my pictures, I only have the adapter plate installed, and really did not have a problem getting a good draw once I got the fire in the middle of the oven. If you have any winds at all, you probably won't melt your canopy. All a short pipe will do is get the heat closer to the canopy so I'm guessing you should just go for it. That is if you don't mind the possibility of a little smoke staining underneath. You could also run a box fan to blow the heat out - something I considered till I saw how little heat I was putting out.

[Larry P]

Not sure what style you're planning for your oven, but if I was doing a minimal roof, I'd probably lean towards a weathered metal roof like e.g. Hell's Backbone Grill in Utah: