DIY castable refractory

[mikku]

Re: DIY castable refractory

Gudday mikku
Your missing the point the ovens was complete in 2008 ..... Still working . I recon that fits the bill .
Regards dave

Not missing anything...read what I said, I won't screw around with something with unpredictable properties when the real thing is not expensive!

[stonecutter]

Re: DIY castable refractory

Boy, I have to disagree again! Sand by no definition is aggregate!

Some useful links

pg 11 Aggregate Specifications
and Requirements

Construction aggregate

Pg 8Carbonating and Hydraulic Mortars

[cobblerdave]

Re: DIY castable refractory

So we agree here.

I would not use it because- unpredictable qualities.

I think that pre-mix is actually cheap for what you are getting. If you do a small oven, maybe 2 or 3 bags! $75 wow---That is a bargain! Why screw around with homebrew? Even if it works--to some degree---don't see any price advantage.

Calling sand aggregate goes against everything I have ever heard--. Sand is fines.

Gudday mikku
Your missing the point the ovens was complete in 2008 ..... Still working . I recon that fits the bill .
Regards dave

[stonecutter]

Re: DIY castable refractory

Calling sand aggregate goes against everything I have ever heard--. Sand is fines.

All non-binding elements of mortar or cement are considered aggregate. Fines are part of graded aggregate.

[mikku]

Re: DIY castable refractory

So we agree here.

I would not use it because- unpredictable qualities.

I think that pre-mix is actually cheap for what you are getting. If you do a small oven, maybe 2 or 3 bags! $75 wow---That is a bargain! Why screw around with homebrew? Even if it works--to some degree---don't see any price advantage.

Calling sand aggregate goes against everything I have ever heard--. Sand is fines.

[david s]

Re: DIY castable refractory

Davids,
The question brought up was about the homebrew. Do you use homebrew in the ovens that you manufacture for sale? Do you use sand molds for the domes and special transition pieces that you manufacture? Or only in the prototype stage when you are trying to figure out what you want something to look like?

I did not see you as being critical of my form building, I probably would use sand at some point if I am trying to create something different. Gee whiz, they use sand all the time to make precision machine parts cast from a variety of materials--but I think we are talking about two different sand castings--aren't we?

The OP's question was about a homebrew castable mix for a homemade oven. I did not provide an opinion about the suggested mix apart from advising about the possible addition of stainless steel needle reinforcement and polypropylene fibres. Since you have asked no I don't use a homebrew to make my ovens, but I am not making a one off homemade product. The advice I did give was regarding moulds and again no I don't use sand as a mould also for the aforementioned reason. However, I have had experience building ovens using a sand mould (I've built three using this method) and found that it is a highly efficient method.
Regarding a homebrew mix, I have no idea how it would hold up in the long term, but I have advised two locals to use it as a castable mix in conjunction with sand moulds. They both report good results. I suspect it won't be as good as a proprietary castable, but better than cob. In fact the proprietary stuff in many ways exceeds our needs. They use high temp aggregates not sand (and yes sand is an aggregate). The reason sand is not used as an aggregate is because it is likely, in the presence of fluxes, to turn to glass at high temperature. We don't need to worry about that because we never get the oven hot enough. My castable for instance is designed to 1450 C some three times greater than we need. They are however, designed to be sintered and that is not possible unless fired in a controlled way in a kiln to around 1000 C. Without this sintering the refractory cycles through heating and cooling in the 500- 650 C range where there is a massive jump in expansion rates of certain materials. This leads to damage of the refractory particularly for large cast sections, creating very small cracks probably mostly invisible to the eye. The thing won't fall down though because of its form.

[cobblerdave]

Re: DIY castable refractory

Gudday mikku
Sorry check out " brick less oven on a shoe string" in the other oven types section. That oven was built in 2008.
Regards dave

[mikku]

Re: DIY castable refractory

Boy, I have to disagree again! Sand by no definition is aggregate!
I agree with post #4 of Deejayoh---if you are going to try to make refractory at least have the right ingredients!

What you have is nothing similar to the real thing that is sold commercially so you cannot compare costs or performance or quality. It is the real thing to ???? thing... (I was going to say "nothing" instead of the ????) but I guess you find some usefulness for the stuff you make.

But really, don't compare it to castable refractory!

[cobblerdave]

Re: DIY castable refractory

The aggregate is the 3 parts sharp sand. Its is not soup like at all.
Minimal water. Too much water then you will have soup. Just add enough
water to wet it and get the reaction going. Its like building a
sand castle at the beach. Not rocket science.

Gudday michelevit
Had a call from a friend this morning , he was very excited in reading about your cast oven. He has had a cob oven before that he had to destroy when he moved house. As he rents and will possible move again he wants to make a movable or at least a semi permanent oven that he can at least take away in parts.
Your oven has been built for a while judging by the date of you joining.
Would it be possible for a link to your build or some more details or pics
Thanks
Regards dave

[michelevit]

Re: DIY castable refractory

The aggregate is the 3 parts sharp sand. Its is not soup like at all.
Minimal water. Too much water then you will have soup. Just add enough
water to wet it and get the reaction going. Its like building a
sand castle at the beach. Not rocket science.

The homebrew you are describing has no aggregate so it must be like soup. The portland cement as described all over this forum is not a refractory material. But if you insist on calling this slurry refractory then so be it! I don't do things like you do--a little bit of this and a little bit of that. So we have some basic differences.

Enjoy your coffee and donuts

[mikku]

Re: DIY castable refractory

The homebrew you are describing has no aggregate so it must be like soup. The portland cement as described all over this forum is not a refractory material. But if you insist on calling this slurry refractory then so be it! I don't do things like you do--a little bit of this and a little bit of that. So we have some basic differences.

Enjoy your coffee and donuts

[michelevit]

Re: DIY castable refractory

When you add up the costs of your components, what does your homebrew cost per 25kg?

Much much less than the premade...

How much time did it take to scurry around and find the ingredients from the different sources?

i have a material supply store that carries all the ingredianent (sand, portland, lime and fireclay) so no scurrying around. Just ask for what I need at the counter and its loaded into my car. Also free donuts and coffee if I go in the morning.


How much time does it take to accurately measure the proportions so that you get a consistent blend between batches?

not long at all.

One scoop cement,
One scoop sand
one scoop lime,
one scoot sand
one scoop fireclay.
one scoot sand.

mix dry and add minimal water.


Homebrew works just fine.


With the premix castable, it is a rush to mix to the times stated and place the material. But the result is a glass smooth casting that is superior in appearance to the ones marketed in Ireland that need multiple scribes and cuts to come into alignment.

If I am doing a "homemade" project, I'd like it to turn out equal or better than the manufactured units, otherwise it isn't worth the effort!

Is 250 dollars too much to pay for a 225kg casting?

I see using homebrew as having too many variables to produce a predictable consistent product. Sourcing the ingredients and making sure each is fresh and clean without other contaminants IMHO isn't worth the effort.[/QUOTE]

[mikku]

Re: DIY castable refractory

Davids,
The question brought up was about the homebrew. Do you use homebrew in the ovens that you manufacture for sale? Do you use sand molds for the domes and special transition pieces that you manufacture? Or only in the prototype stage when you are trying to figure out what you want something to look like?

I did not see you as being critical of my form building, I probably would use sand at some point if I am trying to create something different. Gee whiz, they use sand all the time to make precision machine parts cast from a variety of materials--but I think we are talking about two different sand castings--aren't we?

[mikku]

Re: DIY castable refractory

When you add up the costs of your components, what does your homebrew cost per 25kg?

How much time did it take to scurry around and find the ingredients from the different sources?

How much time does it take to accurately measure the proportions so that you get a consistent blend between batches?

With the premix castable, it is a rush to mix to the times stated and place the material. But the result is a glass smooth casting that is superior in appearance to the ones marketed in Ireland that need multiple scribes and cuts to come into alignment.

If I am doing a "homemade" project, I'd like it to turn out equal or better than the manufactured units, otherwise it isn't worth the effort!

Is 250 dollars too much to pay for a 225kg casting?

I see using homebrew as having too many variables to produce a predictable consistent product. Sourcing the ingredients and making sure each is fresh and clean without other contaminants IMHO isn't worth the effort.

[michelevit]

Re: DIY castable refractory

I've built using sand mold and can attest that it is a good way to cast an oven.
I also used the homebrew recipe and found it perfect for my needs.
We're not building a bridge- we're building an oven.