36" Pompeii Build in the desert

[Gulf]

Let me get this straight. I'm old, so bare with me . You had 1 roll. That's 50 square feet. You need 75 square feet for 3 layers. You just ordered 2 more boxes. That's a total of 150 square feet, counting the box that you already have?

[jim lofaro]

Ouch, my math/logic is suspect. I may end up with an extra roll. Anywho here id the blurb from FB on their blanket "One blanket covers 42 pizza oven dome (1 inch thick)". We will see.

[jim lofaro]

Just looked up the formula for a hemisphere (2 r²). Using a 2' radius comes out to be 25 sq. feet for a 1 inch layer. Looks like I may be returning a roll.

[jim lofaro]

Started on the ceramic blanket. Cut a one foot radius dome yamaka and then blanket sections in 8 inch widths. Placed the 8 inch sections vertically and tapered the sides. Any thoughts about this configuration?

Also has anyone heard of DAP product called High Heat Mortar?

[JRPizza]

Keep your insulation scraps for your insulated door

[jim lofaro]

Finished with the 3 layers of inch ceramic blanket. Glad to see that in the rear view. Starting on the lath. Used concrete screws around the bottom of the lath but just ran out of steam to finish.

[jim lofaro]

My plan is to put on a 2 inch layer of p-crete next. Is this a good idea?

Also I was planning to add a 1 inch brass pipe as a vent at the top of the dome. Is there a better material for a vent?

[david s]

Jim, you have plenty of insulation with 3” of blanket. The perlcrete layer, as well as acting as an insulator, creates a firmer substrate onto which you can stucco. It also allows you to get the form back to a more spherical surface as the blanket can be somewhat lumpy. I use a 10:1 ratio because I want to get max insulation value from that layer, but if in your case, because you have a thick blanket layer, i’d be making it more like 7 or 8:1 which will be easier to apply. An inch and a half should be plenty thick enough. Gulf set up an elaborate jig to ensure the layer is perfectly spherical. But I find just eyeballing the profile is remarkably accurate and tapping the surface with the flat of your trowel does an ideal job.
Regarding the vent, I think a brass fitting set into the outer stucco layer will work well for you. If it has a thread you can screw a cap on and off as required. With my ovens the outer shell is hot to the touch after 3/4 of an hour of firing if the insulation layer is moist. If it’s dry the outer shell will be stone cold until 2 hrs of firing when it will be just cosy warm. Each oven design is different though, you will get to know your own.

[jim lofaro]

Thanks David as you also answered my next question as to the ratio and jig. Do u have a lot of rain in your area? We generally get 12 inches/year with most occurring between July and August. Not much humidity most of the time (102 degrees yesterday with 12 % humidity).

[david s]

We get an average of three times your rainfall and in our dry tropical wet season, ovens will pick up moisture from the air in high humidity even if it hasn’’t rained. Constant use or a couple of long gentle fires restores the oven to normal.

[Gulf]

I agree with brass being a suitable material for the vent. 1" is a bit large for oven vent imo. I do recommend some way to make sure that the pipe and/or fitting is mounted stabily in the stucco layer to prevent it from turning when capping, uncapping or adding a hood. This is what I did for 1/2" pvc.

EDIT: We average about 61.5" of rain a year. And, the humidity numbers.................you wouldn't believe. I'm glad that we don't have your high temps to boot .

[shanxk8]

Been reading posts about pressure relief vents lately. I'm wondering what release seeing pressure is suitable. Most I've seen have been 50 to 150 psi. 150 psi obviously send too high, but is 50 psi alright?
i also saw a 5 psi vacuum relief valve, but suspect that opens the wrong direction. :P

[david s]

The function of the vent is to allow the moisture to escape. Rather like a hole in a saucepan lid, basically the bigger the better IMO (sorry Joe) In the worst scenario the pressure could build up and crack the outer shell, but it’s not the pressure so much as just allowing the moisture to escape so the insulation can dry and perform properly. I did have a pressure problem on about my 5 th oven when doing the curing fires after rendering the outer shell over a vermicrete layer that wasn’t properly dry. I now always do the drying fires after insulation and before applying the outer shell, much safer.

[UtahBeehiver]

Gulf's idea was to use a breather vent (found at most auto parts stores for less than $10). He graciously sent one to me during my build and I incorporated into my build. It is not a pressure valve but rather a vent for water vapor to egress.

[Gulf]

Been reading posts about pressure relief vents lately. I'm wondering what release seeing pressure is suitable. Most I've seen have been 50 to 150 psi. 150 psi obviously send too high, but is 50 psi alright?
i also saw a 5 psi vacuum relief valve, but suspect that opens the wrong direction. :P

There should be no PRV installed on the oven vent imo. It should be unrestricted. I'm not aware of an oven build that has included one.