Mortar mix question and why lime?

[Ken.thai]

I've been trying to figure out what the best mix to make mortar for my oven, after doing some research - I just got more questions than answers

On Forno bravos website I found two different diy mixes: (https://www.fornobravo.com/pompeii-o...mortar-primer/)

A: DIY Heat-Resistant Mortar

• 1 part Portland cement
• 3 parts sand
• 1 part lime
• 1 part fireclay

B: DIY Calcium Aluminate Mortar

• 1 part Calcium Aluminate
• 3 parts sand
• 1 part lime
• 1 part fireclay

On another site I found these two formulas:

C: Refractory Fire Clay Mortar

• 2 part Portland cement
• 10 parts sand
• 2 part lime
• 3 part fireclay

D: Refractory Calcium Aluminate Fire Clay Mortar

• 3 parts Calcium Aluminate
• 10 parts sand
• 1.5 parts fireclay

Does anyone know what the best mix is? Or doesn't it differ that much?

I'm in Thailand and have limited access to supplies, but I got hold of this so far:

1. Portland cement
2. Sand
3. Fireclay (i think, see pics) it says refractory mortar, but on the product sheet it contains, Alumina (Al2O3) 30.5 %, Silica (SiO2) 61.5% and Iron Oxide (Fe2O3) 2.0% which according to wikipedia is fireclay.. correct?

I'm having trouble finding lime though, most people think I mean the green fruit here Is lime necessary? I have tried to google what it does, but doesn't find any good explanation..
I think I found the correct translation for "hydrated lime" now (แคลเซียมไฮดรอกไซด์), so i will go for a hunt tomorrow.

Over and out pizza lovers

[david s]

Caution against using the recipe that includes calcium aluminate cement with lime because the lime acts as an accelerant reducing the already very short working time. Most builders here have found the 3:1:1:1 (sand Portland cement, hydrated lime, powdered clay) perfectly adequate, cheap and highly workable, with sufficient working time.

[UtahBeehiver]

As David describes in last post. Fireclay is just powdered clay that is used for bricks, pottery, etc, it is not a mortar. The DIY 3.1.1.1 is a solid mix that hundred of builders have used.

[Ken.thai]

Thanks for the answers guys! I think fireclay and clay is two different things, no? On wikipedia it says: The chemical composition typical for fire clays are 23-34% Al₂O₃, 50-60% SiO₂ - which is exactly what's in the bag I got in above post. So when you say fireclay, you don't refer to this, but something else? - sorry for the confusion

[Ken.thai]

So now my question really is, what mix should i use for my fireclay, sand, portland cement and lime ? still 3.1.1.1? Or try get normal powdered clay instead? (if so, what then is this fireclay i got used for?)

[david s]

The stuff you have in the bag says it’s refractory mortar.
There is a difference between cement and mortar. Cementious materials are calcium aluminate cement, OPC (ordinary Portland cement and either hydraulic lime or hydrated lime. All of these cementious materials will react chemically with water to go hard.

Mortar is a mix of cementious material and a fine aggregate, usually around 3-4 parts aggregate to ea ch part of cementious material.

Aggregates are not cementious ( the won’t react and go hard with the addition of water and once dry will return to their original state if wet down again. Aggregate materials include sand, grog (ground fired/sintered clay) and powdered unfired clay.

I think what you have in that bag is refractory martar, a mix of calcium aluminate cement and high temperature aggregates comprising grog and powdered clay. It should be ready to go, just add water. But be careful calcium aluminate cement goes off really fast so you won’t have much working time. Only use small batches.

By contrast the homebrew 3:1:1:1 has a much longer working time and is way cheaper.

I hope this clarifies things for you.

I’m presuming you are using this mortar or homebrew as a mortar for a brick build rather than as a castable mix.

[Ken.thai]

The stuff you have in the bag says it’s refractory mortar.
There is a difference between cement and mortar. Cementious materials are calcium aluminate cement, OPC (ordinary Portland cement and either hydraulic lime or hydrated lime. All of these cementious materials will react chemically with water to go hard.

Mortar is a mix of cementious material and a fine aggregate, usually around 3-4 parts aggregate to ea ch part of cementious material.

Aggregates are not cementious ( the won’t react and go hard with the addition of water and once dry will return to their original state if wet down again. Aggregate materials include sand, grog (ground fired/sintered clay) and powdered unfired clay.

I think what you have in that bag is refractory martar, a mix of calcium aluminate cement and high temperature aggregates comprising grog and powdered clay. It should be ready to go, just add water. But be careful calcium aluminate cement goes off really fast so you won’t have much working time. Only use small batches.

By contrast the homebrew 3:1:1:1 has a much longer working time and is way cheaper.

I hope this clarifies things for you.

I’m presuming you are using this mortar or homebrew as a mortar for a brick build rather than as a castable mix.

Thanks for the detailed explanation, much appreciated!

Regarding the mortar I got, this is one of my confusions.. Because, I think it's not mixed with any cementius material - I think it is fireclay! According to the fact sheet on my "mortar" it states:

• Alumina (Al2O3) 30.5 %
• Silica (SiO2) 61.5%
• Iron Oxide (Fe2O3) 2.0%

And according to wikipedia, this composition IS fireclay: https://en.wikipedia.org/wiki/Fire_clay - you get why I get confused?
The shop said, yeah it's ready to go.. But I tried to mix this shitz with water, and it doesnt really set like cement.. I reckon its fireclay hey

[david s]

Try wetting the sample you mixed up. If it does not return to mud then you can assume it contains calcium aluminate cement. If it turns back into mud it is clay only.

[Ken.thai]

Try wetting the sample you mixed up. If it does not return to mud then you can assume it contains calcium aluminate cement. If it turns back into mud it is clay only.

Cheers mate, I tested it and after a day it havent set at all like cement, just crumbled..