Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

[david s]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

I work with proprietary castable and home brew all the time so shall throw in my .02c worth. Most castables have been designed to withstand temperatures way in excess of the temperature range in which we fire. My product is rated to 1450 C which is around three times hotter than we require. Attempting to find their recipe will run you into a dead end as they are closely guarded secrets, but they contain aggregates that are stable at very high temperatures and not required in our case. The stuff is however designed to be "fired" ie taken to a temperature w hich sinters the product. Failure to do this results in a weaker product and in addition the repeated cycling through the 500+C range is damaging as considerable chemical changes and rapid expansion of materials takes place in this range. Both home brew and castable do work for our application although I would have no idea how long home brew will last as it has not undergone industry testing.
Regarding reinforcement for both castable and home brew, the strength can be enhanced with a number of methods. My preference is stainless needles, although rebar and chicken wire may be effective too. The disadvantage of rebar is that as it is relatively thick and much more heat conductive then it gets hotter than the refractory that surrounds it resulting in greater expansion and therefore damage to the surrounding refractory. Needles allow the heat to dissipate more easily to the refractory that surrounds them. Rebar is also subject to rust in the presence of heat and moisture of which there is plenty in an oven. The problem with chicken wire is the ovens temperature. Zinc melts at around 400C so who knows how protective it will be over time. For these reasons stainless steel needles are the preferred and recommended reinforcing for any castable refractory and although expensive are probably the best solution.

[Tscarborough]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

That is close, Dave, I would only add that the clay and sand are there to reduce shrinkage cracking.

It is important to remember that mortar is not used to hold things together, it is used to hold them apart. That is to say, it allows units that do not fit perfectly to be used to build a cohesive structure. Joint size and aggregate size are tied together, and joint size is tied to unit size and regularity.


Concrete (castable) is not mortar and the requirements are totally different, having in common only some of the same ingredients, refractory or not.

[michelevit]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

You're right, decades of testing, chemical engineering and common knowledge are overrated.

I'm not discounting the fact that commercially available engineered products work, just that a much cheaper more readily available home brew version does as well.

so once again

one part portland
one part lime
one part fireclay
three parts sand
mixed dry
add minimal water.

This mixture once cured will form into a rock hard structure that will survive many years of scary fires and can achieve the desired 90 second pizza. It will not crumble, crack or disintegrate.

[cobblerdave]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

Gudday
I was of the understanding that the Portland cement component of the homebrew was the "glue" which held the structure together till the dome was completed and fired. Then fired the Portland would break down in the heat and the lime component would harden and provide the long term glue to prevent the mortar from crumbling. The clay component was only there to provide a more workable and plastic mortar during construction.
Once the dome was complete and fired the mortar instead of being the glue that held the structure up,the mortar was now the cushion between the brick during heating and cooling. The strength of the forno oven was in the fact it was a dome structure not in the strength of the homebrew mortar.
Anyway that's my take on homebrew mortar, its perfect for what it's designed to do but to expect to do something else...
As for michelvits oven. If an adobe oven can work why not. But for how long?
I would like to see a current photo now that I think about it
Regards dave

[Tscarborough]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

You have said that in your instance it worked, nothing more nothing less. Stonecutter and myself are both in the masonry industry, and as such, do not give advice based upon anecdotal evidence. We give what is known as "best practice" advice, and do so for a very good reason: For you it worked, and that is good. For the next person, it may or may not, based upon too many variables to predict. With best practices, you are almost guaranteed a successful project within a broad range of variables, because that is what they are: What works on a consistent basis.

It is up to the individual to make the call on what to use, but hopefully they will listen to best practice of the industry, not anecdotal advice.

[stonecutter]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

You're right, decades of testing, chemical engineering and common knowledge are overrated.

[michelevit]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

In 2008 I built a brickless pizza oven using the homebrew formula and it has not disintegrated. It has survived countless firings and shows no sign of failure. No cracking. No spalling.

The refractory manufactures are in the business of manufacturing and selling
refractory. I already know the answer they will give me.

I have proven that the homebrew does work as a refractory casting material.
Why is everyone so adamant that it wont work? It does work. Its is what is used
to hold a traditional brick oven together.

[Tscarborough]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

Because calcium silicate hydrate and calcium hydroxide (primary hydration products of portland cement) both begin disintegrating at around 500 degrees F.

When used as a mortar in a thin joint, this is not an issue as most of the other reaction products that are produced are able to withstand oven temps, but it DOES matter when used in mass applications (cracking and spalling).

[stonecutter]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

Portland cement when mixed with fireclay, lime and sand at a 3:1:1:1 WILL sustain
high temperatures.
I've built an oven and using the 3:1:1:1 as refractory and it works great.

If it were to fail at high temps as you claim, wouldn't all the brick pizza ovens that use this as formula as mortar would fail, no? The mortar is subjected this same heat.

Portland on its own is bad, but mixed with fireclay, lime, and 3 parts sand works great
as mortor and refactory.

I've done it and recommend it.

For the last time, 3:1:1:1 is not a refractory mix.

And no, brick ovens will not fail with this mix because they are not dependent on the mortar to hold it together. A brick dome ( or vault) has gravity, friction, and reinforcement ( as in reinforced cladding), working with the mortar cohesion to keep the structure together... a cast dome does not.

Castings are reliant on the material used, and are enhanced with reinforcement. If the material fails..spalling, degradation, crumbling...then the dome has failed or is in a state of failure. Some of the cracking issues are solved by segmenting the dome, but with a poor mix, it is only a matter of time. Some refractory mixes do contain some Portland, but nowhere near the ratios used in the 3:1:1:1. It is there primarily for early strength, that is about it...the bulk of the binding and strength is from Alumina, Mullite, Magnesia, or Silica.

Having spoken with several refractory manufacturers, they all concur with what I am relaying here.

I am not trying to convince you....this info is for someone considering 3:1:1:1 for a cast oven. Call a ceramic engineer or speak to a tech at the refractory manufacturer like I have, they will tell you the same thing about Portland in a high temp application.

[michelevit]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

Portland cement when mixed with fireclay, lime and sand at a 3:1:1:1 WILL sustain
high temperatures.
I've built an oven and using the 3:1:1:1 as refractory and it works great.

If it were to fail at high temps as you claim, wouldn't all the brick pizza ovens that use this as formula as mortar would fail, no? The mortar is subjected this same heat.

Portland on its own is bad, but mixed with fireclay, lime, and 3 parts sand works great
as mortor and refactory.

I've done it and recommend it.

[stonecutter]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

If you have never worked with the homemade refractory mix, why do you think portland is not a good idea?

What I said, was that I have never developed a homemade REFRACTORY mix.

I have used bagged refractory mortars like Heatstop50 and others brands, multiple times, on multiple builds. The 3:1:1:1 mix is NOT, repeat, NOT a refractory mix. It is considered fire mortar...a heat RESISTANT material, not refractory. Why?.......

Portland is not a refractory material, ie: it does not maintain it's strength at high temperatures. Therefore, it is not a suitable material for sustained high temperatures. This is not my opinion, it is a fact, and very well documented.

So, seeing as how this is not a personal project, and that optimum quality ( and correct use of material) is at the forefront of the OP's objective, then using Portland in a refractory application is folly, based on the facts.

[thickstrings]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

Because portland, don't quote me, breaks down around 600f and these stoves will get 3 times that hot , in the combustion chamber....

[michelevit]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

I have never worked on developing a homemade a refractory mix design, but I can tell you that using portland cement ( component of the 3:1:1:1 mix) for your application would not be a good idea.

It doesn't appear that you have though. Pics of your test brick would be cool.

If you have never worked with the homemade refractory mix, why do you think portland is not a good idea?

[thickstrings]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

Do you have a opinion on the rigidizer in the above edit?

[RocketStoveBuilder]

Re: Your Advice Re: HomeBrew Castable Mix Greatly Appreciated

tsrings,

mass heater.

As you've observed, bells are more expensive, much more in many cases, which is why we are starting with mass heaters.

Once we can manufacture our own flues, bells will our next project.

Our first rsmh heats our shop - nicely too I might add. Not as hot as a wood stove and the next morning, because of the heated mass, the chill is not there when we go to light the stove for the day. Very nice.

Buying silica sand yesterday at the local bldg. supply, we scored enough scrap cut-offs to heat our shop for a few weeks, free. More free fuel where that came from too.