Barrel Vault Design in NC

[Ron-NC]

I have been following many threads for years to gather information and have now started my build. I have decided on a Barrel Vault design which will be easier for me to build and use for baking bread, roasts and of course pizza.

I have sourced most of my materials which include 100 year old clay solid bricks and medium duty firebricks. The firebricks will be used on the cooking side of the oven and a second layer of the red clay bricks will be added on top of the firebricks to add mass. My expectation is this will allow the oven to hold the heat for a longer number of days. The other reason for the two types of bricks is for economy as the red clay bricks are 1/3 the cost of the firebricks. I have plenty of time to build the oven (retired) so my own extra effort to double up the layers is not an issue.

This brings up my first question. Since the red clay bricks are not uniform, I was thinking of applying a thin layer of home brew on the red bricks to get a level surface, letting it dry, and then use sand / fireclay as my final leveling material to set the firebricks on top of the red clay bricks. Does this sound reasonable or should I use sand / fireclay for all the leveling? The thickness of the leveling material could be as much as a 1/4".

[Ron-NC]

I finally found a supplier about an hour away, for some Lime to use for the home brew - the product is described as "autoclaved finish lime", which hopefully will work fine in the home brew mortar and a stucco finish down the road. The supplier also had two grades of silica sand - fine and medium - the medium should be useful for the wider gaps of the bricks and the fine for the gaps where the bricks abut. Here are some pics of the project.

The foundation is part of a larger slab poured by a redi mix company. The total thickness for the oven area is about 9" with 3/4" rebar for reinforcement. Concrete block was then set and filled with hand mixed cement (ouch!) in every other block core. 1/2" rebar was spaced every 12" or less. I read somewhere that bending the rebar would provide better support, so I used a board wedged under the car to gain leverage to bend the rebar.

Next, the forms were set and 28 bags of cement later (with a mixer this time) the oven slab is done. The slab is covered with blankets and kept wet to have a nice slow cure.

[Ron-NC]

Here is a pic of a temporary side table built to support the cement mixer which worked out great to pour the cement right into the form. There is also a pic of the two types of brick being used in this double layer build. Lastly there is a pic of how the rebar was bent under the weight of the car.

[Gulf]

Ron,

Welcome to the forum. It sounds like that you are well on your way to building the barrel vault design. It also sounds like you are a little further along with the build than your last post. Try using the camera icon in the top left hand corner of the reply screen.Your posts will then appear with thumbnail pics that expand to full size photos.

[Ron-NC]

Thanks Gulf for the advice about using the camera icon - I will try this with the next batch of pics. By the way, your build is amazing - way beyond my skills but lots of great ideas none the less.

[Caliea]

Hi Ron,
Congratulations on starting your build! I look forward to following your progress. Where are you located? I'm near Washington, in eastern NC, on the Pamlico River

[Gulf]

Nothing that I have done is above anyone's potential skills. I'm an old brick layers helper. Some of us that have "laid a brick or two" can have some bad habits and misconceptions about how an oven actually works. What amazes me, is those who have never laid a brick in their life, that "knock an oven build out of the park". You can bet that they did their research on this site. I have no experience with a barrel vault. However, I have seen several who have started out to build one, that converted to a pompeii before the actual build .

[Ron-NC]

Hi Caliea,
We are near Kitty Hawk. Good luck on your build - looks great and you are really moving!

[Caliea]

I'm moving fairly quickly for now, but with kids/family/soccer/life, I imagine we'll hit a roadblock soon. I'm hoping the entire project will be done by Thanksgiving - depends on weather and energy levels! Glad to hear you're so close - maybe we can road trip sometime to visit your oven

[Pizza Julian]

Hi all. I finally found a supplier with fire bricks at $1.50 , neither to say I paid more about to $2.50 for my first 80. Getting closer to build my 42" pompeii . I have a question for you guys and gals . Can I use Old Castle lime carry by ACE that is intended for garden soil additive?

[crisp]

Hi Julian,

There are many different types of lime, but because all are referred to as "lime" it all becomes a little confusing.

I'm not sure of this product you mention, but lime for the garden is basically calcium carbonate (limestone) which is today normally crushed to a powder, it is normally not burned "calcined". If you are using a cement based mortar, this type of lime will become part of the aggregate and improve workability, but only the cement will be the binder, theres nothing wrong using this as purely a plasticiser, but think of this only as part of the aggregate.

Hydrated lime (normally sold as builders lime) is where limestone is burned "calcined" in a kiln to produce quicklime, which is then "dry slaked" with the right amount of water and then normally crushed to a powder (Builders lime). This also will improve plasticity in the cement mix but will also become partly a binder alongside the cement, because it hardens through carbonation (intake of co2 air)

Hydraulic lime is a binder and will harden both by carbonation, and a chemical set in the presence of water (similar to cement). A hydraulic lime will harden chemically under water without air similar to a cement. Whereas a pure hydrated lime builders lime needs air co2 to harden. There are different strengths of hydraulic lime which all can be used without cement added if preferred, it is normally more expensive than hydrated lime, but in my opinion don't need to add cement which is an added cost.

Answer to your question; If you want to use this garden lime to improve fattiness/workability to your mix that's fine, but I wouldn't use it alone as it is not a binder.

Chris

[Ron-NC]

Adding to what Chris said, it is possible the old castle product is calcined (some of the buzzwords to look for are hydrated, autoclaved, type S, ASTM 206 or ASTM207). The supplier may say it can be used for agricultural purposes but given the much higher cost to make a calcined product vs. a pulverized (crushed) version, this probably does not make sense. Still, if this is the only supplier you have found in your area, then contact old castle for product specs to see what they say.

[Ron-NC]

While I wait for the hearth concrete base to cure, here are some specifics of the floor plan. I am using two types of Roxul rockwool insulation for the most part (comfortboard and batt), but did recently purchase 1" ceramic fiber board as the first layer of insulation. For example, the area under the hearth bricks (excluding the arch walls) will have 4" of Roxul topped with 1" of ceramic fiber board. Since the Roxul board is not as dense as the cermic fiber board, the Roxul hearth area insulation will be surrounded by a 5:1 perlcrete base on which the arches and walls will sit. I have read from many builders that 5:1 perlcrete should be plenty dense to support the arches. The insulation is done in this fashion to bring down the cost of the project as the Roxul product is 1/3 the cost of fiber board.

[UtahBeehiver]

I looked at the cut sheet for the Roxul Comfort Board and it a good thermal ratings. The compressive strength is quite low abt 3 PSI at 10% compression vs 90-100 PSI @5% compression for CaSi board.but since you are ringing the wall/vent sections with 5:1 pcrete the only potential would be possible settling of the brick floor since I recall your original design is red clay bricks topped with fire bricks. Just take a look at the compressive strength not just the density before you make the final decision.No going back one the floor is down.

[Ron-NC]

Thanks for the specs Utah, I did think the comfort board was 8 psi.
I am hoping the 1" ceramic fiber on top of the Roxul will distribute the weight evenly in the event there are any soft spots on the Roxul. The double brick floor is floating on the insulation, so if the Roxul compresses slightly it should not matter. This is quite hypothetical on my part though, so we'll see what happens. Worse case I can redo the floor since it is floating i.e not attached to any walls at any point.