3:1:1:1

[stonecutter]

Re: 3:1:1:1

Anyone out there prepared to build an oven with 6:1:1:1 and report back on performance?
The thing that isn't covered by any standard is the heat performance of a portland cement based mortar. It isn't a refractory, and we are just trying to get by with it.
If, as is often put forward on this forum, the portland cement burns out, we are back to 4:1 aggregate to cementitous material. Not such a strong mix.

I don't get the 4:1 thing, because clay is cementitous. It was used as an early mortar which is still used in parts of the world. I correspond with a Mason in Tanzania that builds cross vault ceilings with handmade brick, using clay mixed with sand as the mortar. The thing most people don't understand is the need to match mortar strength to the unit installed. I didn't see anything in the early posts suggesting that the recommended,and often used 3:1:1:1 is a bad mix design, only that it is rich.

[Tscarborough]

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.

[Tscarborough]

Re: 3:1:1:1

A picture is worth a thousand words, so here are some pictures. On the left, 6:1:1:1 , on the right 3:1:1:1. I used a 1/2 cup as the unit of measure.



The lean mix took 1-1/2 cups of water, the rich 1-1/4.

[Tscarborough]

Re: 3:1:1:1

Both are workable and sticky, but as you can see from the joint picture, the rich was a lot more messy.

[Tscarborough]

Re: 3:1:1:1

Lean mix:



Rich mix:



I made 2 samples in plastic cups to play with after they set (and to see how fast they set).

[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.

[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.

[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

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





And I made another sample cup to play with later:

[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

"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.

[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.

[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

It ain't grog unless it has been fired.

[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?