Cast Refractory Pizza Oven Build

[abulsamman]

Here's another pic..

[abulsamman]

Made the sand form today, and put wet newspapers on top then place the wire mesh..
And finally poured the dome

Sooo freakin happy that I have passed this stage. I hope all goes well when removing the sand and brick from within..

[abulsamman]

more pics..

[abulsamman]

Hey Wotavidone! The mix was 1 part Fondu cement, 1 part crushed firebrick, and 1.6 parts Basalt course aggregate - 0.4 to 0.7mm I think..

It is very different than the recepies on this forum, but I tried to follow Fondu's instructions specifically, except I had to add loads more water than instructed since I was using crushed firebrick..

Gotta keep sprayin water for the time being ...

[JoeyVelderrain]

Very nice, I'm impressed

[dragonsoup]

The amount of water you use is directly proportional to the finished strength of the concrete. In concrete engineering the water to cement ratio is the most fundamental property of concrete. If you are using double the amount of water that the manufacturer recommends then you are seriously compromising the strength of your mix.

For increased workability order a "super plasticizer" concrete admixture over the internet which will make the concrete flow much better. Also, order an "air entrainment" admixture which will improve the durability of your oven by making it better able to survive repeated high temperature fluctuation. The air entrainment admixture will also make the concrete more workable.

Hope this helps.

[wotavidone]

Air entrainment admixture would turn your concrete into insulating concrete, would it not? I'm pretty sure that that is how they make Hebel, a.k.a. Autoclaved Aerated Concrete. In the case of Hebel, I think they add powdered aluminium that reacts with lime to form bubbles of hydrogen and "foam" the concrete.
This would be detrimental to the operation of the oven, I would have thought, as the dome is intended to have thermal mass.

Its true that excess water is bad for the ultimate strength of your concrete, but that view has to be tempered with the understanding that the crushed firebrick required wetting with water. The pore water in the crushed firebrick is probably not availabe for reaction with the cement.

I don't have a suggestion for how to get around this problem, but it seems a common theme with people using cement fondue that their agggregates soak up water and they end up using more than the recommended amounts. Perhaps a few people who have used it could report back on their success/failure rate.

[david s]

I encountered this exact problem when making an insulating castable. I used crushed insulating firebricks as an aggregate and they are way more porous than dense firebricks. They took up lots of water. I wet the crushed firebricks prior to mixing with the dry castable, then added more water. Consequently I had no idea how much extra water I added but I did end up with a pretty good result. If I had used the recommended amount of water addition the mixture would have been too dry to place in the forms. The proprietary castables contain fine aggregate and the recommended water addition has been worked out already. They are not designed for the addition of other aggregates so you have to make up the proportions yourselff.

[dragonsoup]

Originally Posted by wotavidone

Air entrainment admixture would turn your concrete into insulating concrete, would it not? I'm pretty sure that that is how they make Hebel, a.k.a. Autoclaved Aerated Concrete. In the case of Hebel, I think they add powdered aluminium that reacts with lime to form bubbles of hydrogen and "foam" the concrete.
This would be detrimental to the operation of the oven, I would have thought, as the dome is intended to have thermal mass.

Its true that excess water is bad for the ultimate strength of your concrete, but that view has to be tempered with the understanding that the crushed firebrick required wetting with water. The pore water in the crushed firebrick is probably not availabe for reaction with the cement.

I don't have a suggestion for how to get around this problem, but it seems a common theme with people using cement fondue that their agggregates soak up water and they end up using more than the recommended amounts. Perhaps a few people who have used it could report back on their success/failure rate.

These are interesting points. As far as air entrainment goes I do not believe it will make the concrete perform like an insulating mix. Dense refractory concrete weighs about 120-130 pcf while the insulating stuff weighs about 35 pcf. It's a totally different product. The biggest differences being the aggregate used in the mix and the proportion of alumina.

Air entrainment should only affect the ability of the concrete to handle the strain associated with thermal expansion and contraction. However, I don't think air entrainment is necessary as a super plasticizer will make a horrible mix flow like water.

As for the fire bricks absorbing water, this is a distinct possibility I didn't think of. Perhaps you should run a test. Take a cup of the crushed fire brick, place it in a fine mesh bag, and soak it in water. Measure the volume of water before you submerge the bricks and then again like ten minutes later after you remove. Then you can at least get a benchmark for how much water a cup of crushed aggregate will take out of your mix and adjust from there.

In any case, good luck with the build.

[david s]

"As for the fire bricks absorbing water, this is a distinct possibility I didn't think of. Perhaps you should run a test. Take a cup of the crushed fire brick, place it in a fine mesh bag, and soak it in water. Measure the volume of water before you submerge the bricks and then again like ten minutes later after you remove. Then you can at least get a benchmark for how much water a cup of crushed aggregate will take out of your mix and adjust from there.

In any case, good luck with the build.[/QUOTE]"

It is easier and more accurate to weigh a sample before and after adding the water.
It is recommended to soak bricks for 24hours to test their porosity.
Hope this helps.