Greetings and question

[Amalgam]

Hello guys I am so impressed and thankful to have found this forum. I am s complete newbie and I am going to build my first pizza oven ever. Due to the lack of real estate for a big one I will build the one made with the gym ball. I have read enough to understand the common mix of vermiculite or perlite and Portland cement. My question is should I put a layer of refractive blanket followed by some stucco or that would be an overkill? Thank you for any input.

[david s]

I presume you are speaking of the portland, vermiculite/perlite mixture for the whole oven structure. While you'll get an oven that works using this method, you'll not have an oven with any thermal mass to do any retained heat cooking and the oven will cool really fast unless a decent active fire is maintained. In addition the insulative concrete mix is quite weak and subject to damage via knocks and abrasions. A far better method would be to do a layer of home-brew 3:1:1:1 sand, cement, lime, clay around 2" thick and then cover that in at least a 3" layer of 10:1 vermicrete. Don't forget to insulate under the cooking floor, usually 5:1 vermicrete. And use fire bricks for the cooking floor also around 2" thick.

[Amalgam]

Thank you so much David for your answer. Yes, my idea is to construct the entire oven structure with mix. I am trying to avoid very thick walls or shell in this case. So is that possible to use the 3-1-1-1 mix you described and cover it with the FB insulation blanket followed by another layer of cement or stucco to cover the blanket?

[UtahBeehiver]

You can use ceramic fiber blanket as you mentioned directly over the dense home brew that David is taking about, or you can , as he suggested use a 10-1 vermiculite or perlite/concrete mix over the home brew dome for insulation. Plus one for ensuring you have insulation under you dome and floor. Ceramic Fiber blanket is a high tech material, rather expensive but has superior insulation characteristics per inch of insulation. With V or P crete , which is less costly, you can stucco right directly on it. With CF you will need to install a structural layer to stucco to.

[Amalgam]

Thank you so much both of you guys I will take the recommended route. I will report with pics later.

[david s]

Thank you so much David for your answer. Yes, my idea is to construct the entire oven structure with mix. I am trying to avoid very thick walls or shell in this case. So is that possible to use the 3-1-1-1 mix you described and cover it with the FB insulation blanket followed by another layer of cement or stucco to cover the blanket?

Yes. From your original post i got the impression that you want relatively quick and cheap solution and that is why I suggested the home-brew would be an improvement over the perl or vermicrete mix. If you want a better mix again then a proper refractory dense castable would be a superior solution but more costly. Whatever type of castable you use 1.5" thick for the inner dense layer would be the min for strength. As Russell suggested you can use the blanket for insulation instead of the 10:1 vermicrete, but it's more expensive. The 10:1 mix is more difficult and time consuming to apply but leaves you with a nice firm substrate to stucco onto whereas the blanket is pretty spongy and works better with a layer of at least 1.5" thick over it.

[Amalgam]

I am going to start the inner shell with the home-brew mix. Any advice in how big of a batch should I mix at a time. Since I have a mixer I was planing in mixing 50 lbs of each of the three ones (Portland, lime,clay) and 150lbs of sand, but after reading some posts it looks like it is not a good idea.

[david s]

You get plenty of working time with homebrew unlike castables that use calcium aluminate based cements, especially as you’re building in winter when the materials are cooler.you main problem will be to get the consistency right as it needs to be stiff enough to stand up vertically on its own. This is particularly important at the base of the dome and wher you need to start. Personally I find it easier to mix the materials in a barrow because it is far easier to get the correct consistency by feel rather than using a mixer where you are making your judgement by eye. If the mix is too stiff you are more likely to get voids, if too fluid it will slump. Once you’ve gone high enough the walls begin to slope in and the mix can be made more fluid. I find it best to place the mix by hand ( wear gloves), place a handful on the base and use one hand on the outside to get the correct wall thickness and the other on the top, creating a flat top to receive the next layer. Proceed until you’’ve gone all the way around the dome, then do the next layer on top of the first. This is fairly quick, but small batches are better than big ones for reasons explained. When done wrap the whole thing to hold in the moisture for at least a week to enhance strength.

[Amalgam]

Thank you again David. Tomorrow I will start and will post some pictures to show my progress.

[Amalgam]

First and foremost “HAPPY NEW YEAR”. I know today is a holiday but I took advantage of that and I started my oven. I already put the first shell made with the 3:1:1:1 homemade mix. How long before I put the 10:1 vermiculite/cement layer? I read a post that I believe said one week but cannot find it again so I just want to confirm that information. Also have many hours of covered cure process before I let it cure open in the air. Thank you so much

[UtahBeehiver]

See your thread post 8, David indicated 1 week.

[Amalgam]

Thank you Utahbeehiver. No wonder I didn’t find it I was looking outside my own thread. What a moron I am LOL