3:1:1:1

[Tscarborough]

Re: 3:1:1:1

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

[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

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

[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.

[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.

[david s]

Re: 3:1:1:1

Fire clay is fired and ground high aluminum content clay with little to no hydraulic properties.

I think you are confusing Fireclay with grog. In its processing Fireclay is not fired.
On another point, if the Portland cement gives way at around 300C which is a temp that we exceed, why do we need it? Wouldn't a lime clay sand mortar be just as effective or is there some other interaction going on with the Portland?

[Tscarborough]

Re: 3:1:1:1

It ain't grog unless it has been fired.

[david s]

Re: 3:1:1:1

Fire clay is a naturally occurring material that is decomposed rock. The weather has done the job of wearing it down to extremely fine particles. It does not react chemically until it reaches 573 C. At lower temperatures the clay only acts mechanically, ie it wants to stick to itself because the particles are so fine, rather like fine sand will dry as a hard lump if wetted and dried.Fire clay is not fired and ground up (in Australia at least). That material is known as grog and is used as an aggregate to open up clay bodies.

[Tscarborough]

Re: 3:1:1:1

When portland cement (actually calcium silicate hydrate as the result of the reaction) decomposes it just degrades back to it's constitute parts minus the H20. It changes from being a binder to an aggregate, basically.

[Tscarborough]

Re: 3:1:1:1

"If he just said it's way stronger than it has to be, fine. But saying it's too strong implies the recipe that's been recommended by many people on this forum, including Forno Bravo, might actually increase the risk of failure of the oven."

I am not implying anything, especially that the 3:1:1:1 mortar will lead to failure. I am offering that the mix design designated by ASTM c-270 will offer a better mortar than the former.

"What do you mean when you say that. A lean mix has lower compressive strength. Do you mean the construction of brick, mortar, brick would have more tensile strength, or the mortar itself?"

The higher the compressive strength in a cementious material, as a rule, the lesser the tensile strength and the more "brittle" the material will be. In an oven, this is really the design criteria by which the mortar mix design should be developed.

[cobblerdave]

Re: 3:1:1:1

Gudday all
Have been watching this with interest. Can I bring up one point , it was my understanding that the Portland cement content was only there for the initial hold and that it would eventually break down under the heat produced by the oven leaving the lime to provide the "long term glue".
If I could suggest Tscarborought "cooking" the samples in a WFO?
By the way Tscarborought I think everyone appreciates you willingness to produce the samples and lead this discussion

Regards Dave

[Tscarborough]

Re: 3:1:1:1

It seems workable, I just question the ultimate bond strength:





And I made another sample cup to play with later:

[Tscarborough]

Re: 3:1:1:1

Back when I started in the industry, 20 odd years ago, most masons would take fireclay and add enough water to make a thick slurry (no aggregate), about like pancake batter, and just dip the firebrick into the mix to lay up fireplaces. I have seen some of those fireplaces and they are in good shape 5, 10, 20, or 100 years later, but! the joints are 1/16--1/8th inch, and it is very easy to take them apart.

3:1 fireclay:




It took 1 cup water to get a workable mix, but it was plenty sticky:

[Tscarborough]

Re: 3:1:1:1

My hands are already dirty, so I will make a 3:1 fireclay mix too to see if it will hold together.

[stonecutter]

Re: 3:1:1:1

Stonecutter, our friend in Tanzania is using an iron rich silicious clay which has strong hydraulic properties. Fire clay is fired and ground high aluminum content clay with little to no hydraulic properties.

Interesting..I am going to talk to Erik further about this.

I still wouldn't consider clay as an aggregate but as a binder...whether it is cementitious in nature or not.