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  #21  
Old 03-16-2013, 03:50 PM
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Default Re: 3:1:1:1

I realize that it would take some serious Google-Fu to find a free C-270 specification so let me summarize it for you.

ASTM C-270 allows for 2 methods by which to specify a mortar:

Proportion specification
or
Properties specification

Proportion specification is the one we are using, it denotes a mortar type by the volumeteric amounts of each ingredient. Mortar types are designated M,S,N,O, respectively in order of design strength, although the proportion specification does not call out or require a specific strength for each and there is no allowance given for either field or laboratory testing. This is the most common for all but government work. See chart below:



Properties specification is used when the physical properties of a mortar are thought to be critical, i.e. when free money is involved, AKA known as the Government. It requires that the actual physical materials to be used be tested in a laboratory under given conditions (ASTM C-780, Standard Test Method for Preconstruction and Construction Evaluation of Mortars for Plain and Reinforced Unit Masonry). This is expensive and is often abused and misunderstood to think that you can grab mortar off a mason's mortarboard and test it. Not allowed. This is the properties chart showing required strengths:



I doubt any of that will mean much, but at least it gives you an idea of what is involved.
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  #22  
Old 03-16-2013, 04:10 PM
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Default Re: 3:1:1:1

Let me also explain why I think that the mortar we use for homebrew should fall in the Type N range or less. The first problem with homebrew is that we can't (or shouldn't) use the sand called for in C-270 (ASTM C-144 masonry sand).

ASTM C-144 is designed for standard 3/8"-3/4" joints and the sieve ratios are optimized for that joint size. Optimally for an oven, we want zero joint at the face, which realistically translates into 1/8 to 3/8" on the face. The sand required for this joint is both finer and more consistently sized than that specified in ASTM C-144, which is why I often recommend laying the units with one type of mortar and parging the back with another.

Given that we are usually using the wrong or right-on-the-edge sand, it is even more important to not make the mortar too strong, as it will overpower both the aggregate and the units and cause cracking in the mortar joint.

Using the proportion specification and guidelines and considering that the fireclay is an aggregate and our sand differs from C-144, by making Type N mortar, we are in fact making a Type O which is appropriate for the brick and the end use.
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Old 03-16-2013, 04:20 PM
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Default Re: 3:1:1:1

Quote:
Originally Posted by Tscarborough View Post
3:1:1:1:1 is not really correct either, it is 3 parts sand by volume of the cementious ingrediants, and lime is considered a cementious ingredient, so the actual ratio is: 6:1:1:1.
So, 3:1:1:1:1 (is there now a new ingredient in the mix?)

Given that clay is not a cementious material then it would be considered an aggregate, so the ratio would now be 4:1:1 aggregate, lime cementl,or 2:1 aggregate, cementious material. Marginally stronger than the recommended 2 1/4 ratio

Last edited by david s; 03-16-2013 at 04:23 PM.
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Old 03-16-2013, 04:28 PM
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Default Re: 3:1:1:1

My fingers got carried away there.

Fire clay can be hydraulic or it can not be hydraulic, it depends upon the clay, but regardless it has volume. The allowed range is for differences in sands, i.e. sharp sand, beach (rounded) sands, silica sands, granitic sands, etc, but the overiding goal of the mortar is to provide workability, bond strength and the capacity to resist cracking from any source.

Last edited by Tscarborough; 03-16-2013 at 04:36 PM.
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Old 03-16-2013, 06:59 PM
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Default Re: 3:1:1:1

By all reports the 3:1:1:1 home brew performs (FOR OUR APPLICATION), as well as and in many cases, better than commercial refractory mortars. That's good enough for me and I'm sticking (pardon pun) to it.
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  #26  
Old 03-16-2013, 07:47 PM
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Default Re: 3:1:1:1

No worries.
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  #27  
Old 03-16-2013, 08:21 PM
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Default Re: 3:1:1:1

But isn't Tom saying a version with less cement could perform even better? I've built multiple ovens with home brew, but there is always room for improvement.
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Old 03-16-2013, 09:07 PM
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Default Re: 3:1:1:1

Quote:
Originally Posted by shuboyje View Post
but there is always room for improvement.
Someone has to take the first step in suggesting a new or different idea.....
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  #29  
Old 03-16-2013, 10:30 PM
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Default Re: 3:1:1:1

I tell you what I think, not what you should do, that is up to you.
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  #30  
Old 03-17-2013, 06:02 AM
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Default Re: 3:1:1:1

Quote:
Originally Posted by wotavidone View Post
Personally, I think the confusion comes from applying house building knowledge to refractory work.
From all that I have read, including a manual from the local cement manufacturer, that 3 to 1 sand to cement is normal every day brickies mortar.
Lime is considered cementitious, and arguably the fire clay, since it doesn't get fired hot enough, is not. (Yes, I know, fired fire clay is considered cementitious, but I don't thing that is what most people get when they buy a bag of clay. And the stuff from the tray under the wetsaw has already been hydrated, how cementitious can that be?)
So at this point we might argue the ratio of sand+clay to cement + lime is 2:1 in the homebrew. A very rich mix indeed if you are building a house. If anything moves the bricks might break before the mortar gives.


As Brickie and many others have pointed out the job of the mortar is to keep the bricks apart, and I don't contest this at all, when building a house or the stand for the oven. However, for an oven, I actually want it to stick the bricks together. A strong brew in this situation is a good thing, I reckon.
In any case, there should be no confusion. Who cares what the science says - 3:1:1:1 is widely reported as being a very successful mortar for pizza ovens.
An oven is more dynamic than a wall or building, so the idea of a leaner mix, which would have greater tensile strength, is a good improvement
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