Cast oven build in Shelbyville, KY

[sriceky]

It has been a few years since I decided I want a wood fired oven. This forum has been incredibly helpful and a couple of months ago I decided to go for it. Some of my design criteria are:
- Somewhat moveable. I have no immediate plans to move the oven, but I want the ability to move the entire unit to a new location if and when I move. I plan that any move would involve some serious equipment.
- Cast - I know how projects can extend indefinitely and I wanted an oven that would be finished by the end of this summer
- Not too big. Don't need a huge oven and although wood is cheap where I live, I still don't need to burn through cords of wood.

My oven is going to be a 28" diameter cast oven with 2" thick walls. The stand is a welded steel stand with a 3-1/2" steel reinforced poured hearth.

I am lucky enough to be near a great maker space - www.firstbuild.com - and to by signed off on a number of pieces of equipment - including a water jet. I used the water jet to cut the 8 corner brackets and the lower horizontal pieces. The stand is welded with angle iron on the top to hold/support the poured hearth. The lower section is meant to hold wood and I used a series of pipes inserted into the water jet cut horizontal pieces. I capped the pipes with extra large rivets. Once the stand was wleded and cleaned up, it was back down to FirstBuild where I powder coated the entire stand.

The following weekend I built a set of forms and poured the hearth,

[sriceky]

[sriceky]

Once the hearth cured and I ripped the forms off, I cut firebrick for the floor. My floor will be inside the dome. Managed to pick up a great 10" wet saw with a damaged pump for $50. A $17 pmp later and I have an incredible wet saw. Only took about a 2 hours to get everything cut to how I like it.

[UtahBeehiver]

FYI, to keep the pump from clogging with brick sediment, several of us have extended the supply hose and placed the pump in a Homer bucket with fresh water rather then in the saw water tray. This way the pump always has a clean water source. BTW, nice looking iron work on your stand and great start on the floor.

[sriceky]

Even though I believe everybody that says a sand mold is easy and quick, I went a different route - mainly because I had a bunch of rigid foam insulation hanging around. I build an inner mold out a stack of foam pieces cut on a bandsaw - I still need to smooth off a few of the corners at the top since my bandsaw was limited to a 50degree cut. They are glued only around the outer edges so that they will come apart easier when I cut them up and pull them out of the dome's opening. I also decided to build an outer mold, mainly because I had the time and this way I can ensure that I maintain a 2" wall thickness. The outer forms are built in 6 layers. Each layer is pinned to fit with the layers above and below. I will start with just a single layer and add castable refractory - add another form layer and more castable until I completely form the dome.

[fox]

Cool, I like it!
What are you going to cast it with? Do you plan a one piece dome? Are you going to vibrate the mix? Do you plan to add S/S needles or any other additive?

[sriceky]

I am going to cast with a product available locally - LouCast27. I've spoken to the technical guy at Louisville FireBrick and this is the castable that he has used for multiple pizza oven builds. He hasn't used SS needles in the past and while cracks do form, they have never caused any issues. I do plan to agitate the castable as it is poured. While this will be a single piece dome, it will be poured in 3.5" layers. I plan to pour as fast as possible but agitating each "layer" as it is poured. The plan is to start with just the lower outer form in place and add form layers as the pour progresses. This will give me good access to agitate the mix as I go. The agitation will simply be inserting a rod into the mix and shaping. The inner and outer form will allow me to pour a wetter mix than if I was just using an inner form. I've got a buddy coming over to help and with the use of a Harbor Freight paddle mixer, I expect this pour to go very quickly.

[david s]

Just be aware that making the mix too wet, in an effort to eliminate air bubbles, can result in lower strength in the casting because the extra volume taken up by more water, once it's been eliminated, will lower the density. Although I've found that most castable manufacturers' recommendations for water addition leaves you with a mix that is too dry. It is possible to use some superplasticiser to increase fluidity if you have inner and outer moulds, but be extremely careful as it has a much more powerful effect with calcium aluminate cements than with Portland cement. It is easy to overdo it and end up with separation of the materials.
Regarding the stainless needles, they will increase the strength, but as you say the fine cracks don't really cause an issue. Most manufacturers don't use needles, at least they don't say so in their product descriptors, probably because they're expensive and make handling the wet material difficult and make the dry, set castings a bit dangerous where the odd bit of needle protrudes.
Ther is also an issue in making the dorme in one single casting in that there will be uneven heating and therefore uneven expansion leading to stress in the dome casting. This is a problem for all large cast sections. Because of the way you are casting and the design of your moulds, you could easily design a join so the top 1/3 of the dome casting is a separate piece. This is where a natural crack will occur anyway, as that section gets way hotter and faster than the rest. If you get up to about that height simply allow the casting to set for 24 hrs, apply some release agent to the join, then finish the top of the casting. That way the crack occurs wher you want it to.

i hope the LouCast27 is a dense castable. The name suggests it could be a low density product, which is not what you want.

[sriceky]

That sounds like a good idea. I'll doo the bottom 4 layers one day and the top 2 the following day. What would you suggest I used as a release agent between the two castings?

LouCast 27 is a dense castable. I found the specs a couple of months ago and they were inline with you have recommended in the past. I made another post about that product at that time.

Thanks for the hints!

[UtahBeehiver]

I'll let Dave answer for sure but I believe he lightly uses 50/50 kerosene and motor oil mix.

[david s]

There are lots of things you can use as a release agent. I use a 50/50 mix of motor oil and kerosene on my moulds, but for you to separate your casting layers you could use slip (mix of water and clay), or a pva release agent.

[sriceky]

Just realized why David thought that LouCast27 might be a low density castable. The Lou in the name is for Louisville. The manufacturer/supplier is Louisville Fire Brick. The product has a density of 130 lbs/ft3 (2.1 Kg/liter).

[fox]

There will be a big difference between rodding the cement mix or vibrating the mix.
I filled my first dome mould & tried various methods of getting the air out including an orbital sander & a hammer drill with a wooden dowel in the end (my mould is made from GRP) The next one I cast I used a hired vibrating poker, the difference was instantly noticeable!
I fill mine in three sections, after filling the fist ring, I stuck in the poker & watched the mix literally fall down about a 1/2 inch. You can see all the air bubbling on the surface but the most obvious difference is the final product that will be far smother & lack any air holes or voids.

[cnegrelli]

I used WD-40 as a release e and had no problem.

[sriceky]

Fox- what size was the vibrating poker - almost everyone I have seen is about 1-1/2" in diameter - my form walls are only 2" apart.