Clay Mortar

[dimitrisbizakis]

Hi everyone, i was wondering, i have found an old factory that was making clay bricks.
I've got some bags from there and it contents is 98% clay and 2% silt.
I have already used this clay with 50% sand to make a dome for an cob oven.
Can i use this clay with fine sand and perhaps some lime as a mortar for building the dome?

[david s]

Re: Clay Mortar

Hi everyone, i was wondering, i have found an old factory that was making clay bricks.
I've got some bags from there and it contents is 98% clay and 2% silt.
I have already used this clay with 50% sand to make a dome for an cob oven.
Can i use this clay with fine sand and perhaps some lime as a mortar for building the dome?

Yes you can, but if the mix contains a high proportion of clay you will get shrinkage cracks. Use the home brew mix ie. 3:1:1:1 sand, cement, clay, lime. This mix works well and has proven to be a cheap and superior mortar for WFO's.

[dimitrisbizakis]

Re: Clay Mortar

Yes you can, but if the mix contains a high proportion of clay you will get shrinkage cracks. Use the home brew mix ie. 3:1:1:1 sand, cement, clay, lime. This mix works well and has proven to be a cheap and superior mortar for WFO's.

What's the difference of the clay i have found and the fire clay everyone says?
I mean, the clay i have is not a light gray but it can handle temp's up to 1000C (tested on a cob oven) so what is the worst scenario that can happen?

[david s]

Re: Clay Mortar

What's the difference of the clay i have found and the fire clay everyone says?
I mean, the clay i have is not a light gray but it can handle temp's up to 1000C (tested on a cob oven) so what is the worst scenario that can happen?

IMO pretty much any clay should be ok. (others may disagee) You only have about 16% by volume of clay in the mix anyhow. When firing in a WFO the temp only gets to around 500C at max.

[dimitrisbizakis]

Re: Clay Mortar

IMO pretty much any clay should be ok. (others may disagee) You only have about 16% by volume of clay in the mix anyhow. When firing in a WFO the temp only gets to around 500C at max.

Only at 500 "C"?
Are you sure?
What's the purpose of the clay in the mix?
The cement is Portland or refractory?

[dimitrisbizakis]

Re: Clay Mortar

He's sure. It's a pizza oven, it burns wood, there is no fan-forced air, no metallurgical coke or coal, no oxygen injection. In short, it's a wood fired oven, not a blast furnace

Unless you are using a draft door!
Right?

[cobblerdave]

Re: Clay Mortar

Gudday
Disagree mick .like you said the refractory properties are really not required.
What you do get is a great mortar that's plastic,sticks to what is a really smooth surface easily, can handle lager gaps in the brickwork.I think the home brew mortar is what enables a bunch of mug first time bricklayers acheive the results that they do.
I now enough about bricklaying to know my bricklaying skills basically suck but I've built a good solid working oven with the forgiving nature of this stuff. If I built again I would use fireclay in the mortar mix or at least a clay rich brickies loam.

Regards dave

[dimitrisbizakis]

Re: Clay Mortar

Gudday
Disagree mick .like you said the refractory properties are really not required.
What you do get is a great mortar that's plastic,sticks to what is a really smooth surface easily, can handle lager gaps in the brickwork.I think the home brew mortar is what enables a bunch of mug first time bricklayers acheive the results that they do.
I now enough about bricklaying to know my bricklaying skills basically suck but I've built a good solid working oven with the forgiving nature of this stuff. If I built again I would use fireclay in the mortar mix or at least a clay rich brickies loam.
Regards dave

What was your mortar mix Dave?

[Tscarborough]

Re: Clay Mortar

"If you use fired clay, say saved from cutting the bricks, then that is an inert filler"

That is not true, the brick powder has hydraulic properties, and is used in lime plasters to give a quicker set than the lime alone.

[cobblerdave]

Re: Clay Mortar

What was your mortar mix Dave?

1 part Portland cement
3 part sand
1 part lime
1 part fireclay
As per for forno recipe

I have also used a mix using no fireclay but brickies loam ( brickies sand with a clay content ) on an unrelated job and this mix had the same sort plastic character. You can move the brick a bit sqish it down and move it sideways without the brick losing its grip to the mortar.

Regards dave

[Tscarborough]

Re: Clay Mortar

In the lime plaster that I refer to, you should not use ANY portland. Some of the latest research shows that my old rules were wrong. My rule of thumb used to be you could gauge with up to 10% cementious (which would include brick dust or portland) material, but it appears that anything more than 2% is deleterious to the plaster. Mortar is a bit different than plaster/stucco though.

Edit-Googlize "Smeaton Project" for the study. Page 12 of 18 for conclusions.

[Tscarborough]

Re: Clay Mortar

Yes, it is important to note that when talking about brick dust in this context, that it is not FIREBRICK dust, just normal silicious clay brick.

[dimitrisbizakis]

Re: Clay Mortar

Yes, it is important to note that when talking about brick dust in this context, that it is not FIREBRICK dust, just normal silicious clay brick.

Are you talking about plastering only or it can be used as mortar for the Dome?
Why not Firebrick Dust?
Firebrick dust here in Greece is called samot or (at free translation) firedirt and is VERY expensive and i don't know the reason...25 kg costs 20 Euro!!!

[Tscarborough]

Re: Clay Mortar

Because the silica is the hydraulic agent and high alumina firebrick have proportionately less silica. Fire clay is not the same thing as brick dust (and 20 Euros for 25 Kg is cheap).

[dimitrisbizakis]

Re: Clay Mortar

Because the silica is the hydraulic agent and high alumina firebrick have proportionately less silica. Fire clay is not the same thing as brick dust (and 20 Euros for 25 Kg is cheap).

Fire clay is clay higher in Alumina, i guess.
20 Euros is a day's work here...anyway!