Hybrid brick/cast pizza oven and smoker. m

[jes2xu]

Hi everyone,

I think I lost the OG post to the lost days. So I will just start another.

The idea here is to try and keep the build cheap (NZ prices here!) which means going cast rather than traditional brick. But to keep a bottom ring of brick to give a little thermal mass and toughen the oven up around the bottom.

Im scavenging as many materials second hand or ideally free as I can, so naturally the build plan is going to change to incorporate what I can get my hands on. I understand that this is not going to be standing in 100 years, but I hope it should be a whole lot better than what I have right now (nothing)!

Minimal cost upgrades are welcome, equal cost substitutes or changes rock and if you have suggestions that will save me $$ and not hurt the build quality you shall fast become my new best friend!

Dimensions:
Cooking surface: 900mm / 35.5 inch
Dome height: 540mm / 21 inch
opening: 324mm x 480mm / 13x 19 inch (this size where the opening meets the dome, it widens toward the landing)

The base:
Is going to be built with wood . The oven is much lighter than most, and this cuts down on cost BIG TIME. I am also suggesting that having full support under the hearth slab (not just supported on 3 sides) should allow me to have a thinner slab. concrete counter tops are only about 1inch thick! Not that I will go that thin.

The slab:
will be normal concrete reinforced with rep. it will be 2.5 inch / 60mm at this stage.
On top of that I will have a perlite/pumice insulating layer that will be 2.7 inch / 70mm thick

Hearth:
Hopefully will be fire brick of some description, if I can find some that will not break the bank. If not I will resort to the solid red bricks

Brick ring:
If I find a real bargain on fire brick I will use them. More than likely this will end up being halfed red bricks though. 2 high and build under the oven opening as well.
I am keeping my options open though and will consider adding more layers of bricks if I find them cheap.

Cast dome and entrance:
This will be made up of two layers combining to a total thickness of 150mm / 6inch.
The inside layer will be a home-brew cartable refractory 4:1:1:1 Sand, lime, portland, clay and reinforced with SS needles.
The outer will be a perlite/pumice insulating layer of 5:1 + SS needles.

Smoker:
Vents from the fire box on the left into the pizza oven through a 1 brick gap in the second ring. Adjustable vent on the fire box, and the flue is adjustable on the oven.
Firebox is : 400x330 mm (internal area)

Thats how things sit right now. Im sure I will keep you busy with a stream of new questions! Let me know if you have suggestions, or can see a problem with any of this.

[jes2xu]

Question time:

1) I am planning on doing the dense cartable at 50mm / 2inch then the perlite/pumice at 100mm / 4 inch. Does anyone see any problems here? Is the dense going to be thick enough to be strong?

2) I have calculate that the volume of the dome (both layers) will be around 0.26m3. But I have no idea how much mix that is going to take. Just breaking (.26/3) down into the 4:1;1;1 for example will not work right? Im trying to work out roughly how much of everything I need so I can start getting things together.

3) SS needles in both the dense AND insulating right?? How much will I need? Same amount for both mixes?

4) I saw some one mention ( I think it was david s) using pet hair instead of poly fibres to melt off. Is that still legit advice? If so how much?

[david s]

Using the ss needles in the insulating layer is counterproductive because they're very conductive and the mixture is not that strong with the lightweight aggregate, so it probably won't add a great deal of strength.
Regarding the human or animal hair, it was just an idea I had. I've not tried I'd and don't know at what temp it would burn away. You could try a sample and put it in the oven to see what happens (burnt hair smel- yuk). From my experience steam explosions in pottery kilns seem to occur somewhere between 200 and 300 C, so although water turns to steam at 100 C it's not until you get a bit higher that the increased pressure becomes strong enough to cause problems. In pioneering days animal hair was commonly used to reinforce plaster walls.
Try a barbers shop for their "off cuts" Don't use sheeps wool I think it has fire retardant qualities.

[jes2xu]

Ok cool thanks david,

Yeah I may look into the hair then. A quick google seems to say that human hair is burnt off at about 200c. In that case I'm guessing that it should work as intended right? And I guess if it dose not burn off its not going to harm anything right?

Ok so SS needles in the dense layer only then.

What does everyone think about cast in place vs moving it? Pros and cons of each? I like the idea of casting it and then moving it, that way I can cast the dome first. Effectively giving the dome more time to cure while I build the base etc. But I'm guessing a dome of this size will be fairly borderline in terms of being able to move it??

[jes2xu]

I managed to buy these at a price I could afford. They are "firebrick" from night storage heaters.

Im trying to decide how best to utilise them for this build.

Im thinking using the flat square ones on the right for the hearth. But not too sure what to do for the brick ring? Thoughts?

Also considering extending the brick ring up basically until I run out of brick. So build the sandcastle form, mix up home-brew mortar. and start building a brick dome. When I run out of brick I switch over to home-brew castable and finish the dome off.

[david s]

It is difficult to tell from the photos, but are all those bricks clay? The red and the grey look more like concrete to me. Storage heater bricks are designed for storage heaters which do not see the sort of heat in either max temperature or rate of temperature increase that a WFO receives in service. Having said that they may or may not be suitable. You probably won't be able to find out and won't know until you've built your oven and operated it for a few years. Quite a few folk in the UK have used storage heater bricks, as Utahbeaver stated on another thread, and have reported success, so assuming your bricks are exactly the same material you could be lucky. Try looking at ukwoodfiredovenforum

[jes2xu]

Thanks for the feed back David,

I am picking them up today. I have a tornado gass burner I use for brewing. So I plan on putting one of the bricks through heat cycle hell with that and see what happens.

I did do a fair bit of research on the UK/AU forums, seems like the guys that use them consider them a runner up solution to fire brick. And these ones look pretty much what I expected them to. So who knows I guess I will find out in the long run though.

In regards to the clay can I just dig my own if I'm not too worried the refractory properties of the clay?

Getting pretty excited to get started on this now that I'm getting close with materials etc.

[david s]

Try asking for bricklayers clay at a brickworks. If they don't have it they should be able to direct you to where you can find it. Digging your own clay is hard work because you have to dry it, break it up, pulverise it and seive it to remove impurities.

[jes2xu]

I picked up the bricks today, still very happy I bought them. From what I can tell these are the same types of bricks I have seen fellow DIYers have some successes with in the UK.

I got 4 different types of bricks with the purchase. (sorry for the very quick snap shots!) I have descriptions of the bricks on the images.

The bricks that are played out on a mock up of the hearth are flat on both sides and 50mm thick. Unfortunately there are not enough of these to cover the hearth. I think I will substitute them for the flat bricks with the cut out on the back around the back of the hearth where I am unlikely to be cooking pizza etc.

I don't think I will be using the yellow bricks, they are pretty light I think perhaps these are the insulating bricks?

Thinking I may use the more traditional shaped bricks standing on their end around the hearth. there should be just enough to do a full corse, but will have to lay them out.

Thanks David, yeah I hear you. I knew I had to do all of that. I guess I was romancing the idea of doing as many things as I can my self. In the end its just going to slow things down for me though. I will end up being late on the build waiting for clay to dry or something stupid.

[jes2xu]

I now have my soldier corse and hearth planned out. and plan to go ahead with the cast dome pretty much as planned rather than trying to crowbar in using the other fire bricks, although I may do one or two courses depending on how easy they are to cut.

Now that I have a fair bit of fire brick left over I am thinking of breaking the lower quality bricks up to use as Grog ( right name ??)

As I understand it it is worth using some grog in my home-brew castable mix yes? If so at what quantity? Should it replace something else? Right now the castable mix stands as 4;1;1;1 Sand, lime, portland, clay + SS needles.

As a morter to lay the hearth I plan on using the same mix as above without any of the aggregate. Is it worth adding very fine fire brick dust into it? Or is that just pointless?

Getting pretty close to breaking ground, exciting!

[david s]

Crushing up the firebrick is pretty hard work. You'll probably get halfway through the required amount and regret the decision. I know this because I've done a fair bit of it myself. Don't bother trying to crush the insulating bricks because they are full of air and you need a dense castable, so you need to crush the dense bricks if you want to use them as aggregate.

Most castables have pretty fine aggregate. ie nothing bigger than around 5 mm. This is because large aggregate makes the mix less workable. You should probably also discard the brick dust from the mix. It is important to get a variety of sizes with your aggregate. If I were doing it I'd halve the sand quantity and replace the other half with crushed firebrick minus it's dust. Wear a decent mask as the dust from fired clay is dangerous to breathe. As stated in a previous post (I think it was one of those lost posts) I think 4:1:1:1 is not rich enough. It may be ok for mortar because you want the mortar to be weaker than the bricks, but you are making a castable refractory which you want to be stronger than mortar. Also, let's say the Portland gets destroyed from the high temperature and then basically becomes aggregate. The clay component does not get hot enough to form any kind of chemical bond at the temperatures we fire to so it also can be considered an aggregate, it is decomposed rock after all. That only leaves the lime as the "glue" to hold all this aggregate together leaving you with an aggregate to lime ratio of 6:1, too weak IMHO. Increasing the brew to 3:1:1:1 would result in an aggregate to lime ratio of 5:1, more acceptable.

It's your brew, but I'd like to hear anyone else's opinion on this point.
Using home brew for a cast floor is likely to result in a fair amount of cracking. You' be better off laying unmortared firebrick over a layer of insulation (vermicrete perhaps), sitting on a standard mix of structural reinforced concrete.

[jes2xu]

Ah ok thanks for the input yet again David!

I had been wondering about that exact point (lime being the only thing that ends up holding things together). My newby logic seemed to think that more lime could only be a good thing, yet I assumed that there must be logic to it.

Does anyone else have any input on upping the lime to aggregate ratio?

Ah perhaps I didn't make that clear, I will not be casting the floor. I will be using the fire brick on top of insulating brew on top of construction concrete. I was asking more if I could use the home-brew as mortar between the insulation layer and the fire brick. The main reason being that many of the bricks I will be using for the hearth are not flat on both sides. So assuming I place the flat surface up, I will need to be doing a lot of levelling under the bricks to get them flush. This will be especially apparent for the bricks that will be cut (they will then have a high and low side basically)

I had also thought about pre mixing a home brew batch and basically doing a skim coat on the underside of the bricks that are not flat. My reasoning suggests that this would stop cracking as there is no large body of home-brew. and would allow the bricks to be placed more easily on top of dry clay/sand.

[david s]

The normal levelling mix is 50/50 sand, clay. It can be dry or wet.

[jes2xu]

So I just found these guys pretty much right on my door step.

Master Mix
http://www.mastermix.co.nz/special-products.html#

They have a fire mortar with basalt fibers in it that he claims can be used as a refractory castable. Any thoughts? In theory I would agree with him, the basalt rock fibers would act as the stainless steel needles. But the fact that it is called "mortar" makes me worry a little!

Also could I use pumice sand as a leveling mix? Or would that need the clay in it as well?

[david s]

Reading the characteristics of their fire mortar, (short shelf life, fast setting) it sounds very like it is a calcium aluminate product. Ask if it is suitable as a castable refractory and if it is a calcium aluminate.based product. If so it is likely to be expensive. I thought your original reason for using the homebrew was based on cost in which case you may get a shock when you find out the price of the proprietary product.
Re using pumice the answer is yes, but you will have to crush it fine to use as a levelling medium.