#21  
Old 01-02-2014, 02:20 PM
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Default Re: Fireclay? Refractory Mortar? In Utah?

It is important to understand the function of the various parts of a mortar.

The portland serves as a gauging material, i.e. it allows the mortar to set in a reasonable period of time.

The lime is the actual long term binder, as well as an air entraining agent and lubricant.

The clay is a filler like the sand, and fills the smaller end of the aggregate spread. Some clays may also work as a gauging material with the lime.

It is not debatable that portland cement hydrates disintegrate at temperatures above 500 degrees, that is simple scientific fact. If you were to make a straight 1-3 portland sand mortar, the mortar would not last long, although the oven would probably not fail for years. Mortar is used to hold the brick APART, not TOGETHER, and a hemispherical structure is self supporting.
I
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  #22  
Old 01-03-2014, 03:25 AM
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Default Re: Fireclay? Refractory Mortar? In Utah?

Quote:
Originally Posted by Tscarborough View Post
It is important to understand the function of the various parts of a mortar.

The portland serves as a gauging material, i.e. it allows the mortar to set in a reasonable period of time.

The lime is the actual long term binder, as well as an air entraining agent and lubricant.

The clay is a filler like the sand, and fills the smaller end of the aggregate spread. Some clays may also work as a gauging material with the lime.

It is not debatable that portland cement hydrates disintegrate at temperatures above 500 degrees, that is simple scientific fact. If you were to make a straight 1-3 portland sand mortar, the mortar would not last long, although the oven would probably not fail for years. Mortar is used to hold the brick APART, not TOGETHER, and a hemispherical structure is self supporting.
I
Damn right.
IMO the most important part of the mortar is the lime as the long term binder.

Not 100% sure what the clay does, but I've always thought it could be as simple as filler. Is that 500 degrees C or F for the disintegration of the Portland?
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  #23  
Old 01-03-2014, 04:05 AM
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Default Re: Fireclay? Refractory Mortar? In Utah?

Gudday
It's the stuff that makes it " plastic" a stick able and squishy mortar. Using " brickies loam" sand with a clay content ,produces the same effect. Using a commercial plasticizer is the modern way, but a " squit " of mums dishwashing liquid will do. But in all deference to Tsar is the homehandyman way and shouldn't be used on a commercial job.
Regards dave
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Last edited by cobblerdave; 01-03-2014 at 04:07 AM.
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Old 01-03-2014, 10:32 PM
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Default Re: Fireclay? Refractory Mortar? In Utah?

There is some confusion regarding Fireclay. In the refractory or ceramics industry it is a clay that can withstand extremely high temperatures. In the building industry it is just a powdered clay added to mortar to improve plasticity but is usually not a true Fireclay. We do not require a true Fireclay for the temperatures our ovens are fired to, a bricklayers clay will suffice, but remember that a high proportion of clay wil contribute to excessive shrinkage therefore tending to to create shrinkage cracks, so use it sparingly.
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Old 01-04-2014, 05:02 AM
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Default Re: Fireclay? Refractory Mortar? In Utah?

Something worth noting about using Portland in the mortar for ovens, is the fact that almost every oven built on this site is non-commercial. Recreational ovens never receive the same amount of usage as a commercial ones, which you would be hard pressed to find some that were built with a high ratio of OPC in the mortar. 3:1:1:1 is not a new mix design.... Masons have been using that and similar mortars in fireplaces for decades, and they are always site mixed. The similarity between a fireplace and a recreational oven? The mortar is not subjected to super high ( higher than 1200*), constant temperatures. It does last, but how long has to do with many, many variables...so, back by what is already known by ceramic & refractory engineers and masonry heater/fp/oven builders...limit the mortars dependance on OPC.

As mentioned on this thread and many others, OPC is not a refractory material, and needs to be treated as such when designing a mortar mix. Additionally, every component of a mortar design should be suited to the application, according to what is the best material that is available to the builder.
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Last edited by stonecutter; 01-04-2014 at 05:34 AM.
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  #26  
Old 01-04-2014, 05:29 AM
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Default Re: Fireclay? Refractory Mortar? In Utah?

Quote:
Originally Posted by wotavidone View Post
Is that 500 degrees C or F for the disintegration of the Portland?
Starting at 500 degrees Fahrenheit
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Last edited by stonecutter; 01-04-2014 at 07:18 AM.
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  #27  
Old 09-07-2014, 08:28 AM
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Smile Re: Fireclay? Refractory Mortar? In Utah?

The Home Depot has 50lb bags of fire clay
For $5.00
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