3:1:1:1

[david s]

Re: 3:1:1:1

The only trouble I see with using clay as a binder is that it doesn't undergo a chemical change until it is fired to temperatures that are not all that easy to achieve in a WFO. So, not being chemically changed, if it gets wet it is no longer a binder.

Yes, that's another reason why we need to keep our ovens dry. The clay is still a pretty good binder when wet though. It has to have LOTS of water for it to fail. Rather like a mud brick house that is still strong even if the bricks have taken up some moisture.

[Tscarborough]

Re: 3:1:1:1

Portland is used as a gauging agent. It allows building to proceed in a relatively quick manner. Using a sand form, for instance, you could use nothing but fireclay so long as the design allowed for proper buttressing of the dome.

[Tscarborough]

Re: 3:1:1:1

Fireclay is fired, but not to the point that it undergoes the change that would make it grog. You could dig fireclay straight out of the ground and use it, but that is not what is available to most members.

Me making grog:

https://www.youtube.com/watch?v=CNcFwByeUzw

[stonecutter]

Re: 3:1:1:1

The only trouble I see with using clay as a binder is that it doesn't undergo a chemical change until it is fired to temperatures that are not all that easy to achieve in a WFO. So, not being chemically changed, if it gets wet it is no longer a binder.

That it doesn't chemically change does not make clay an aggregate.

[Tscarborough]

Re: 3:1:1:1

9 hours later (8 for the fireclay), the 2 homebrews have set. The fireclay mix has not.

[david s]

Re: 3:1:1:1

Fireclay is fired, but not to the point that it undergoes the change that would make it grog.

So any firing it undergoes is merely to dry it. This is quite different from the common understanding of "fired" which is the irreversible change that takes place at quartz inversion 573C

[Tscarborough]

Re: 3:1:1:1

Exactly, it is dried, pulverized and ground, but not run through the kiln.

[Tscarborough]

Re: 3:1:1:1

And just to be clear, I am not guessing or extrapolating, I have been to the plant and observed the process.

[Tscarborough]

Re: 3:1:1:1

The fireclay mix has still not set, which indicates to me that it has no or very little hydraulic properties.

[Tscarborough]

Re: 3:1:1:1

It is not hydraulic, that is, it is unable to set in the presence of 100 percent humidity. Nominally, clays are considered a binder, but not cementious.

[david s]

Re: 3:1:1:1

My fingers got carried away there.

Fire clay can be hydraulic or it can not be hydraulic, it depends upon the clay.

So what kind of clay would set under. 100% humidity?

[Tscarborough]

Re: 3:1:1:1

A hydraulic one. In the case of the Italian tradition they are volcanic pozzolans, highly siliceous. There are several ways to do it however, and limestone/lime is another way to achieve a hydraulic set to a cementious material.

[stonecutter]

Re: 3:1:1:1

Maybe not, but it certainly means that it can't be considered cementitious in the general sense of the word, and any binding properties it has are reversable by excess moisture.

Aren't we talking about clay used in the oven builds? Clay changes it's physical property after firing. And, I have never seen or heard of clay that was fired lose it's binding property from excess moisture.
Bottom line, when counting out a ratio for refractory mix..you can't say clay is an aggregate. Because clay does fit the general definition of a cementitious material. And, as mentioned earlier, some clay can contain minerals ( iron rich silicious ..I'm waiting to hear more from Erik on this,T) which give it hydraulic properties...which, by definiton, would then make it cementitious.

Semantics aside...when you include clay in the ratio, it does not count as part of the aggregate number.

[Tscarborough]

Re: 3:1:1:1

At a 3:1:1:1 or 6:1:1:1 ratio it does not count as either.

[david s]

Re: 3:1:1:1

Ok, so if it's not cementious or an aggregate, it's somewhere in between and doesn't count. So lets just call it sticky stuff and move on.