Cast Refractory Pizza Oven Build

[shuboyje]

Re: Cast Refractory Pizza Oven Build

Sorry to be a bit late into this topic, but I do have a bit to add. This page has information of the recommended aggregates for use with ciment fondu based on the temperature it will be used at.

Ciment Fondu?

Silica based aggregates(sand) are good for up to 500C(932F), too low for use in a pizza oven for me. The dome in my oven regularly maxes out my 1100F thermometer when at pizza temperatures.

As for dimensions and shape, it looks to me like you are going for a traditional low dome naples style pizza oven. Is that the goal? If it is I would go a bit lower on the dome and a bit smaller on the door, but I can expand on this into more detail if this is what you are after.

[david s]

Re: Cast Refractory Pizza Oven Build

Karim,
Those numbers look pretty good to me. You have obviously been doing your homework. 45 cm in width for the door should give you plenty of room and the door height to dome height ratio is about right. you've also left about the right amount to fit a door in there nicely.

Good luck,
Dave

[abulsamman]

Re: Cast Refractory Pizza Oven Build

Thanks allot Dave and Shuboyje for your input..

I'm still looking for the right aggregates to use, and didn't find the polypropylene fibers yet but there is one company that I'm keeping my fingers crossed for that I still need to check out. If they have a ready mixed castable mortar including fibers that's going to be great!

If that doesn't work, I think I will NOT use sand as an aggregate, but rather crushed clay, crushed red bricks, basalt, or granite depending on what i find.

In regards for the oven dimensions, wasn't sure to chose a high or low vault dome, so dimensions are in between, and according to Forno Bravo's manuals and rule of thumb 63%door height to height of dome..

[abulsamman]

Re: Cast Refractory Pizza Oven Build

got a brick sample for the cooking floor. According to the guy I got it from these are Chinese made bricks made for furnaces, and it could withstand temperatures of 1200 c if I recall correctly, and cost about USD 2.11 per brick..
Have no idea of the alumina content, but did see other Spanish made brick that are smaller in size.

[david s]

Re: Cast Refractory Pizza Oven Build

Make sure they are dense fire brick. That is they should be heavy. If they are really light then they are insulating fire bricks. You don't want them.

[abulsamman]

Re: Cast Refractory Pizza Oven Build

They are defenately dense and heavy, got 80 bricks yesterday and now I'm working on an entry form out of cardboard to see how it looks.

Will post some pics once I'm done ..

[abulsamman]

Re: Cast Refractory Pizza Oven Build

Ok, got some pics of the entry form. Its not 100% but its a pretty good idea of what the entry is going to look like.
I'm going to give it to a carpenter to imitate but ask him to get the dimensions as close as he can get it to my numbers. Although, after making this form I realized that I need to slightly increase the height of the sides of the outer arch (lowest point)..
Still need to add the form for the vent which goes on top of this..

[abulsamman]

Re: Cast Refractory Pizza Oven Build

Finally got the Polypropylene Fiber, it wasn't easy to find as its not widely used here..
The recommended dosage is only 0.6Kg / cubic meter, so really not going to need much as per my estimation I am going to use roughly 0.125 - 0.135 cubic meters of refractory concrete so the total amount required is not more than 100 grams?? could this be right??

Mind you, although 100 grams doesn't sound like much but the stuff is pretty light anyway. It really has a texture of hair.. Got a shot of it below with its data sheet..

[abulsamman]

Re: Cast Refractory Pizza Oven Build

Did the adjustments to the entry form. I have slightly increased the height of the sides of the outer arch (lowest point) to make it more funnel shaped from the top of the sides. Still didn't add the bit for the chimney as I have been really busy, but it should be completed tomorrow..

I'm also planning on laying the bricks for the cooking floor tomorrow, and going to cut them to the right shape. I rented an electric saw and have never used one so hopefully I don't make a mess of things and don't off cut any fingers..

[david s]

Re: Cast Refractory Pizza Oven Build

Finally got the Polypropylene Fiber, it wasn't easy to find as its not widely used here..
The recommended dosage is only 0.6Kg / cubic meter, so really not going to need much as per my estimation I am going to use roughly 0.125 - 0.135 cubic meters of refractory concrete so the total amount required is not more than 100 grams?? could this be right??

Mind you, although 100 grams doesn't sound like much but the stuff is pretty light anyway. It really has a texture of hair.. Got a shot of it below with its data sheet..

That's the stuff. Test a bit out in your kitchen oven and you will find it melts at 160 C. you do need to mix it about twice as much as you think to separate and disperse the fibres.

The addition also sounds about right although you are adding it, not for strength, but for a path for water elimination.

[abulsamman]

Re: Cast Refractory Pizza Oven Build

Thanks for the advice Dave..
Got down and dirty today, and layed the bricks for the cooking floor. Not very happy with the shape of the entry, so going to redo that as well as some bricks that need smoothing out..
I placed the form for the entry in its place just to see how it looks. I think its going to look good

[wotavidone]

Re: Cast Refractory Pizza Oven Build

I think it is going to look excellent!

[abulsamman]

Re: Cast Refractory Pizza Oven Build

Haven't been posting much about my build but here's what been happening..

Made a few concrete samples with the fondu cement. The first sample I made, and as per Fondu's specs on the bag was using 1 part cement, 1.6 parts sand (I used crushed fire brick instead), and I added a sprinkle polypropylene fiber. As their instructions I was supposed to add only 0.4 parts of water, This proved to be extremely dry and unworkable. I know its not easy to work with but this was way beyond that. I kept adding water bit by bit till I reached a reasonable and plasticky feel to it, and that was when I reached almost 1.2 parts of water. That's more than double!

Fondu reiterate not to exceed their 1 part cement to =< 0.4 parts water or that will significantly decrease the strength of the concrete. That got me worried..

Anyway, I kept the cement block (shape of a firebrick) that I made damp for 3 days then I decided to test it. The only way I could think of to test the strength was to hold it from one end and smack the other end on a hard surface. It took me 2-3 hits before it broke.. It wasn't that difficult.. So I thought that this is not the kind of strength I expect for my oven.

On a good note I found that the Polypropylene fiber was evenly distributed. I placed one broken half in my oven, and gradually increased the temperature. Once I reached the 160 to 180 C all the visible fibers had burnt off. Then I maxed the oven to 250 C, for about 1.5 hours and left it to cool till the next morning.

Again I smacked it on a hard surface, but to my surprise the fibers inside had not burnt off! even though when the block was in the oven I measured its temperature with a laser thermometer, and it was over 230 C...

I can only assume that the surface on the outside was hotter than the inside, and should have probably left it for a longer time..

Anyway going back to the strength of my concrete, and the only conclusion I came up to is that I need a course aggregate and not just fine crushed firebrick as I had used in my first sample. The only problem is that I could not fined the right course aggregate anywhere. I went to a granite / Stone / Basalt cutting and carving shop, and asked if they had any gravel like left overs, and they only had semi fine Basalt aggregates much smaller than what I had in mind.

I kept on looking, and found that we actually have a large Basalt mine in Jordan. So I called up their offices not far from where I live and asked if they can supply me with some. They said they only deal with huge orders since they are a mine company, but if I go all they way to the mine they will make sure somebody will help me out. I figured what the hell why not! I took a colleague from work with me in a small van. Surely, after two hours of driving, we saw the mountains of the crushed Basalt that I was looking for. I got around 500 Kg for about 7 USD of course I'm not going to need all of it, but could use the rest as a mulch in the garden or something else..

Last night, I made a second sample (tile shaped) and as per Fondu's specs when using gravel:
1 part cement, 1 part crushed firebrick, 1.6 parts Basalt gravel, the fibers, and tried to only add 0.4 parts water.

Again the water was insufficient, so kept adding till I reached 1.2 parts of water to get it where I want it to be.

Today, the tile sample felt very hard, and I actually cut it in half with a saw and noticed the evenly distributed aggregates. I'm still keeping it damp as it has not finished curing, and once that's done I will check its strength..

Does anyone know why I have to use so much water to get the concrete to become workable?? Is it because I'm using crushed fire brick?

Will the increased water affect the strength of the concrete??

Anyway will post some pics tomorrow..

[david s]

Re: Cast Refractory Pizza Oven Build

If using crushed firebrick you will need more water because the crushed brick is quite porous. you don't say whether the bricks were insulating bricks or dense firebricks. The insulating bricks are easy to crush and quite light. I would't worry too much about the increased water content, just get the mix to a plastic state that you can handle. I recently made up a home brew using crushed insulating firebrick and proprietary castable refractory 50/50 to make a lightweight castable for a kiln. By reducing the density this way it also reduces the strength, but I've ended up with a good result. Yet to fire to prove its performance.

[wotavidone]

Re: Cast Refractory Pizza Oven Build

All the "parts" are by weight according to their spec sheets. So if you are measuring by volume, you'll need a little extra water just to allow for that. Then clay seems to soak up a lot of water that then isn't available for the chemical reaction.
Daves right, add just enough to make it workable.