Building a 42" oven mainly for bread

[UtahBeehiver]

Vcrete or perlcrete are economical options. Either of these options are about 0.5 as effective thermally wise than cf board, IE 6" v or pretend equals 3" cf. DavidS has a table showing the K of vcrete by ratio of cement to vermeculite. If you are on a budget and your build can accommodate the extra height and OD then these type of insulation are an option.

[matthanna]

As you can see, it's quite messy. This was my first ever attempt at brick laying, so i've got a lot of clean up to do. Pretty happy though

[matthanna]

Hi Randy,

Thank you so much for such a detailed response.

I apologise for such a late reply, as I've been very busy building this oven.

For the oven floor and first round of bricks, I was able to get a really thick rectangle fire brick so I don't think I'll need to lay them on their side - each brick is roughly 11cm high/deep. I've taken on your idea of outside mortar.. I'll use the refractory stuff I'll use to secure the dome around it too. For the dome, I was able to get tapered kiln bricks, these are new and left over bricks from a local brick manufacturer after they made their kilns, so should make an awesome dome.

I'm up to the part where I need to decide on hearth insulation. My plan was to use vermicrete, but I'm hearing more and more that I should stay away from it, and your post is added to the list. I really like the idea of fibre board, but I didn't account for how expensive it is. I've managed to find and cost up 2" ceramic fiber board, but it's going to cost more than $600 !!!! I don't have $600 for the insulation layer on a top of the structural concrete. There has to be a cheaper way (sub $500). A friend of mine said to use hebel bricks... they're damn cheap and easily sourced, but I simply don't know if I should be doing that. I've very conscious of heat escaping through the floor, and I don't know how that will stack up. There's a little about hebel on this forum, but Im not finding enough conclusive information to make me go down that way. What do you think?

I will post a picture of my progress after this post.

Apologies again for the lateness of this reply.. I've been hard at work building this lovely oven!!!

Regards,
Matt

[RandyJ]

If you are worried about thermal mass you could set the floor bricks on edge so you will have 4.5"on the floor. You could also render a layer of home brew mortar on the outside of the dome about 1-1.5 "thick. That should give you plenty of bread output. Also do 4" or more of ceramic board insulation under the oven, and don't bother with the vermicreete it is not as good a insulator and is a lot more work. Also do at least 3"ceramic blanket over the top of the dome. Then if you do a enclosure then fill the void with vermiculite as losses fill and you should have tons of thermal mass. It will take more wood and time to heat up, but that is the price you pay for very extended baking. Or if you want to cut it back a little then do the standard oven and a 1\2" cladding and the same insulation and have very good heat retention for baking.

Randy

[matthanna]

Hi All,

New user, first post, so please excuse me if I am doubling up on previous posts (I have tried searching).

I've started building a 42" Pompeii Oven using the Pompeii Oven Plans Version 2.0. These instructions are awesome, but I am struggling to work out a small part regarding the hearth. My wife and I are big bread makers, and plan on making high volume breads with this oven along with pizza.

On page 28 of the instructions, it show how you could add extra heat mass by sinking a brick island into the insulating layer. It says to take care not to reduce the your insulating layer to less than 3.5 inches.

Does this mean that the hearth is comprised of the 3.5 inches of structural concrete, then a 3.5 inch insulating concrete layer, followed by the layer of firebricks that make up the extra heat mass under the cooking floor which could then be surrounded by normal concrete?

I can't imagine that the extra firebricks being set into the 3.5 inch insulating layer would be safe, as it would only leave an inch or so of insulating concrete before the structural concrete layer. If I built the hearth layer as a 9.5 inch rather than 7.5 (being 3.5 structural concrete, 3.5 insulative concrete, 2.5 firebrick surrounded by either insulative or structural concrete) would it be a bad, unthinkable, or unrecommended configuration?

Thanking you in advance!

Matt