DIY castable refractory

[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

[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

[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

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

[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.

[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.

[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.

[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

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

[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!

[mikku]

Re: DIY castable refractory

Some useful links

pg 11 Aggregate Specifications
and Requirements

Construction aggregate

Pg 8Carbonating and Hydraulic Mortars

I guess you proved the point. What a person "me" perceives as aggregate and what the government describes as aggregate are not the same. I guess the government is right. Sounds like a wise ass answer, but it isn't meant to be. Thanks for taking the time to present information that is more than someone's opinion.

[mikku]

Re: DIY castable refractory

Stonecutter,
If you were doing a project that required a castable refractory, would you use this homebrew recipe or buy the real stuff?

[mikku]

Re: DIY castable refractory

Cobblerdave,
If you were doing a project that required castable refractory would you use this recipe or would you buy the real stuff?

[stonecutter]

Re: DIY castable refractory

I guess you proved the point. What a person "me" perceives as aggregate and what the government describes as aggregate are not the same. I guess the government is right. Sounds like a wise ass answer, but it isn't meant to be. Thanks for taking the time to present information that is more than someone's opinion.

It's not only government opinion (only one of those links had gov affiliation), classifying sand as an aggregate is accepted and understood by masons and builders using cementitous materials.

[stonecutter]

Re: DIY castable refractory

Stonecutter,
If you were doing a project that required a castable refractory, would you use this homebrew recipe or buy the real stuff?

I have never given it much thought, mainly because I think unit masonry makes a superior oven.

But to answer your question, I would say it depends on who the oven is for.

For myself, I would definitely use a material I could make at home. My ratios wouldn't be quite the same as the ones posted here, for one, I would reduce the amount of Portland. I would probably make several different mixes before I moulded a dome.

For a client, I would use a bagged refractory product, something with a good reputation for quality. Unless they insisted on using a home made fire mortar to save a buck...then they would get a disclaimer and explanations of the differences, with pros & cons. And, I would only use it if I had a successful ratio and had tested it myself.

I would probably try to convince them to build with brick in either scenario anyway.