42" Pompeii Oven in Jamaica

[wthwaites]

Thanks Petter !

[wthwaites]

**Update**
Finally got to closing up the dome! I put the final keystone piece in today!
The last few courses aren't the prettiest, but its functional and I'm happy with it.
The bricks I've been using are 3.75" deep, so I'm thinking that the next step will be to do either an additional 0.75" - 1.25" mortar render for additional thermal mass. After that I'll install the chimney on top of the dome; I've decided to try the Squirrel tail design...

[MarkJerling]

**Update**
Finally got to closing up the dome! I put the final keystone piece in today!
The last few courses aren't the prettiest, but its functional and I'm happy with it.
The bricks I've been using are 3.75" deep, so I'm thinking that the next step will be to do either an additional 0.75" - 1.25" mortar render for additional thermal mass. After that I'll install the chimney on top of the dome; I've decided to try the Squirrel tail design...

That looks good! I look forward to seeing your squirrel tail.

[wthwaites]

Currently adding 1.25" of additional thermal mass to bring to a total of 5" including the firebricks.

I'm now thinking about how the final layer of my dome should be done after laying my 4" of insulation FB. Is stucco the best option? What is the best recipe mix for this?
Also, I read that drilling holes into the slab where my FB will be should help in the future cure fires with moisture loss and prevent cracking. Is this true and needs to be done or is it unnecessary?

[UtahBeehiver]

Wet insulation is one of the main issues with poor oven performance, it causes the insulation to become a heat sink. If I remember right you have IFBs then some type of CaSi of unknown specs on top. It would of been a lot easier to have installed weep holes in the concrete hearth before the oven started, I would try using the oven several times and see what the performance is. If you feel substantial heat transmitting down to the concrete slap you have wet IFBs and or CaSi then you many have to rethink the weep holes in the slab. Don't forget to install a vent in the apex of the dome in the stucco to steam and egress out.

[wthwaites]

Wet insulation is one of the main issues with poor oven performance, it causes the insulation to become a heat sink. If I remember right you have IFBs then some type of CaSi of unknown specs on top. It would of been a lot easier to have installed weep holes in the concrete hearth before the oven started, I would try using the oven several times and see what the performance is. If you feel substantial heat transmitting down to the concrete slap you have wet IFBs and or CaSi then you many have to rethink the weep holes in the slab.

Thanks a lot for this advice. I already know that the board and IFBs are soaking wet from our rainy season. I just assumed that the cure fires would slowly dry them out. If that's not the case, then I guess its back to the drawing board...

Don't forget to install a vent in the apex of the dome in the stucco to steam and egress out.

I don't understand what you mean. I'm doing a squirrel tail chimney so the flue will be sitting on top of the dome. You're referring to a separate vent? How would I do this?

[UtahBeehiver]

Water that works it way into the dome insulation, and it will, increases in volume by a factor of about 1500 times when it sublimates to steam. Unless you have a way to vent the steam out between the dome, insulation, and stucco the increase pressure in this area due to the volume increase has the potential to crack the stucco. Do a search on the forum for steam vents, are are a number of posts on this subject.

[Gulf]

I'm doing a squirrel tail chimney so the flue will be sitting on top of the dome. You're referring to a separate vent? How would I do this?

I'm not sure how you will carry the weigtht of the flue above apex of the dome if there is a void ffilled with fiber blanket. But, if there is such a void, you may be able to elbow a pipe horizontal from the apex out to where the chimney takes off above the outer shell. It may help if you include a rough drawing of how your chimney/flue is designed.

[wthwaites]

Water that works it way into the dome insulation, and it will, increases in volume by a factor of about 1500 times when it sublimates to steam. Unless you have a way to vent the steam out between the dome, insulation, and stucco the increase pressure in this area due to the volume increase has the potential to crack the stucco. Do a search on the forum for steam vents, are are a number of posts on this subject.

Thanks UtahBeehiver
I'll look search around some more...

[wthwaites]

I'm not sure how you will carry the weigtht of the flue above apex of the dome if there is a void ffilled with fiber blanket. But, if there is such a void, you may be able to elbow a pipe horizontal from the apex out to where the chimney takes off above the outer shell. It may help if you include a rough drawing of how your chimney/flue is designed.

Sorry, I meant that the chimney would sit on the apex of the dome, not the flue.
My original intention was to run the flue system directly on top of the thermal mass before insulation with the fiber blankets and finishing with stucco. Something similar to the design by MarkJerling

If this isn't recommended, please guide me. I'm learning everything as I go along with the build.

[wthwaites]

Water that works it way into the dome insulation, and it will, increases in volume by a factor of about 1500 times when it sublimates to steam. Unless you have a way to vent the steam out between the dome, insulation, and stucco the increase pressure in this area due to the volume increase has the potential to crack the stucco. Do a search on the forum for steam vents, are are a number of posts on this subject.

I like this idea. I think I would put one at the top of my dome, and two on either side at the bottom of the dome in line with the base (IFB and CaSi board). Or would this be overkill?
I also see in other threads that you've recommended a steam vent/breather cap which looks like plastic along with PVC bushing. Won't this melt? I assume copper or brass would be better?

[Gulf]

.....If this isn't recommended, please guide me. I'm learning everything as I go along with the build.

Sorry for my poorly worded reply. I did not intend to cause alarm or to question the squirrel tale design. My intent was only to figure out where would be the best place for a vent, if applicable.

[UtahBeehiver]

No, vent will not see temps to cause any melting problems, it just extends though the stucco layer to the top of the fiber blanket. It is placed at the top of the oven due to steam rises so I am not sure vents at the base give you any benefit.

[david s]

I like this idea. I think I would put one at the top of my dome, and two on either side at the bottom of the dome in line with the base (IFB and CaSi board). Or would this be overkill?
I also see in other threads that you've recommended a steam vent/breather cap which looks like plastic along with PVC bushing. Won't this melt? I assume copper or brass would be better?

The vent can prevent pressure build up like a hole in a saucepan lid. I don't think its placement really matters although as the top of the oven gets hottest first and also driest first and any steam generated moves away from the heat source hitting the cook outer shell, condensing there and running down the sides, it is the base of the dome that remains the wettest, so drains there would be more appropriate. In this case any pressure build up would actually force the steam/water out the drains in a more efficient manner just as drain holes in the supporting slab under the floor insulation do a similar task. My experience firing new kilns where water dripping from the lower front corners of the kiln, once it reached around 400C, taught me this. I have a drawing somewhere explaining this principle, but can't find it. Another rather elegant solution would be to drill some holes in the base of the flue pipe that is surrounded by insulation so steam can pass into the flue pipe. This would then eliminate any external vents on the outside of the dome. My system is something like this (drawing attached)

[wthwaites]

No, vent will not see temps to cause any melting problems, it just extends though the stucco layer to the top of the fiber blanket. It is placed at the top of the oven due to steam rises so I am not sure vents at the base give you any benefit.

Great. Thanks for the advice UtahBeehiver !