limestone vs. brick construction

[wotavidone]

Re: limestone vs. brick construction

Limestone is not lime.

Obviously. However, nonhydraulic lime mortars set by carbonation, i.e. turning back into calcium carbonate (the principal constituent of limestone).

Lime mortar - Wikipedia, the free encyclopedia

So the question still remains - why is this calcium carbonate good when it's providing long term strength to the mortar, bad when it's the masonry unit?

[stonecutter]

Re: limestone vs. brick construction

Obviously. However, nonhydraulic lime mortars set by carbonation, i.e. turning back into calcium carbonate (the principal constituent of limestone).

Lime mortar - Wikipedia, the free encyclopedia

So the question still remains - why is this calcium carbonate good when it's providing long term strength to the mortar, bad when it's the masonry unit?

Show me one example where limestone was or is being used as a liner for a furnace, wood stove, wood oven...or even a fire box in a fireplace. How about limestone burnt in a kiln, ground down then moulded into units used in the previously mentioned applications? You won't. It will spall, delaminate, and degrade with every cycle.

It's weak in that state, and it contains other minerals that react poorly to thermal shock...feldspar and quartz to name a couple. And Lime in mortar is never the only binding component when used in thermal applications ( ovens, fireplaces)....other pozzolins are added, like clay or crushed brick. These add strength and durability to the mortar.

[Tscarborough]

Re: limestone vs. brick construction

Quite frankly, I do not know what purpose the lime serves in home made refractory cement other than as a plasticizer.

[Toomulla]

Re: limestone vs. brick construction

Thanks to all for the responses I agree with all the recent comments, I would say we have established that limestone is not a suitable material for long term success ( if that is all you have got and you don't care how long it lasts go for it) have we also established that the Idea that mortar is flexible or self repairs is incorrect and that we rely on gravity friction and adhesion to keep the components in place with the mortar suction and adhesion assisting while laying the bricks only particularly as the chemical reactions rely on moisture and we strive for a moisture free environment once the dome is complete

[wotavidone]

Re: limestone vs. brick construction

Thanks to all for the responses I agree with all the recent comments, I would say we have established that limestone is not a suitable material for long term success ( if that is all you have got and you don't care how long it lasts go for it) have we also established that the Idea that mortar is flexible or self repairs is incorrect and that we rely on gravity friction and adhesion to keep the components in place with the mortar suction and adhesion assisting while laying the bricks only particularly as the chemical reactions rely on moisture and we strive for a moisture free environment once the dome is complete

I have a lot of unanswered questions, myself.

For example, I question whether lime is only to provide plasticity.

Think Brick Australia represents the brick manufacturers of Australia.
They have an Industry Reference Guide.

http://www.thinkbrick.com.au/system/...pdf?1394520197

Part 2 deals with mortars and references Australian Standard 3700
Two interesting things jump out at me when I skim it.
1) Type M2 mortar is the preferred mortar for fireplaces and barbecues. It consists of 1 part cement, 2 parts lime, 9 parts sand.
2) AS3700 does not permit the use of fireclay as an admixture, which might explain why it's so hard to get at an ordinary hardware store, rather than just the relative scarcity of fireclay deposits in Australia.

It's commonly acknowledged that Portland cement decomposes at temperatures easily achievable in a pizza oven or incinerator. So we'd better hope that the mortar specified by Standards Australia and the industry representative body is using the lime for something other than plasticity while wet, eh? Though the reference guide does extol the virtues of lime for this purpose.

Which brings me back to my original point.
That is, we use lime, which is limestone burnt and slaked to form calcium hydroxide, as at least one of the binders in mortar. Everything I have ever seen on this says that this lime hardens by carbonation. Which is essentially turning it back to limestone. At that point we say the lime component is contributing to the strength of the mortar, and lose no sleep over its durability at pizza oven temps.

Given that using limestone as a masonry unit in a fireplace or oven is considered a bit of a no-no, I'm a bit bemused by the somewhat passionate replies I get for mentioning this apparent contradiction between using lime in mortar (where we expect it to turn back to limestone) and using limestone.
Anyway, all I originally suggested was that since the OP had access to these limestone blocks, and was planning to spend short period of time building a dry stacked oven as an "inexpensive first step towards something more permanent", little would be lost if he gave it a go and it didn't work.

I wasn't suggesting building a fireplace in anyone's house, or pressing burnt lime into bricks or any such nonsense, and I do know the difference between limestone and lime.
Ah, the joys of trying to have a reasoned discussion with the denizens of the internet.

By the way Toomulla, we only strive for a moisture free environment in our oven after we have given the initial moisture time to chemically react with the binders we use, whatever they might be. Concretes and mortars that are allowed to dry out before these reactions take place will be weak.

[Toomulla]

Re: limestone vs. brick construction

I have a lot of unanswered questions, myself.

For example, I question whether lime is only to provide plasticity.

Think Brick Australia represents the brick manufacturers of Australia.
They have an Industry Reference Guide.

http://www.thinkbrick.com.au/system/...pdf?1394520197

Part 2 deals with mortars and references Australian Standard 3700
Two interesting things jump out at me when I skim it.
1) Type M2 mortar is the preferred mortar for fireplaces and barbecues. It consists of 1 part cement, 2 parts lime, 9 parts sand.
2) AS3700 does not permit the use of fireclay as an admixture, which might explain why it's so hard to get at an ordinary hardware store, rather than just the relative scarcity of fireclay deposits in Australia.

It's commonly acknowledged that Portland cement decomposes at temperatures easily achievable in a pizza oven or incinerator. So we'd better hope that the mortar specified by Standards Australia and the industry representative body is using the lime for something other than plasticity while wet, eh?

Which brings me back to my original point.
That is, we use lime, which is limestone burnt and slaked to form calcium hydroxide, as at least one of the binders in mortar. Everything I have ever seen on this says that this lime hardens by carbonation. Which is essentially turning it back to limestone. At that point we say the lime component is contributing to the strength of the mortar, and lose no sleep over its durability at pizza oven temps.

Given that using limestone as a masonry unit in a fireplace or oven is considered a bit of a no-no, I'm a bit bemused by the somewhat passionate replies I get for mentioning this apparent contradiction between using lime in mortar (where we expect it to turn back to limestone) and using limestone.
Anyway, all I originally suggested was that since the OP had access to these limestone blocks, and was planning to spend short period of time building a dry stacked oven as an "inexpensive first step towards something more permanent", little would be lost if he gave it a go and it didn't work.

I wasn't suggesting building a fireplace in anyone's house, or pressing burnt lime into bricks or any such nonsense, and I do know the difference between limestone and lime.
Ah, the joys of trying to have a reasoned discussion with the denizens of the internet.

By the way Toomulla, we only strive for a moisture free environment in our oven after we have given the initial moisture time to chemically react with the binders we use, whatever they might be. Concretes and mortars that are allowed to dry out before these reactions take place will be weak.

I agree entirely at the end of all the discussion most of our constructions will outlast us, so if you longevity is not an issue use what you have and the shorter it needs to last the rougher you can be I.e a dry stack can still cook a pizza the value of the discussion is that readers will little knowledge get exposed to a variety of views

[wotavidone]

Re: limestone vs. brick construction

P.S. I believe that the self healing properties of lime are due to growth of crystals across hairline cracks, I doubt that it'd work in an oven. Crystallisation occurs when things precipitate from solutions such as water based solutions or molten slags. Don't want to see either of those in our ovens.

[stonecutter]

Re: limestone vs. brick construction

Which brings me back to my original point.
That is, we use lime, which is limestone burnt and slaked to form calcium hydroxide, as at least one of the binders in mortar. Everything I have ever seen on this says that this lime hardens by carbonation. Which is essentially turning it back to limestone. At that point we say the lime component is contributing to the strength of the mortar, and lose no sleep over its durability at pizza oven temps.

Given that using limestone as a masonry unit in a fireplace or oven is considered a bit of a no-no, I'm a bit bemused by the somewhat passionate replies I get for mentioning this apparent contradiction between using lime in mortar (where we expect it to turn back to limestone) and using limestone.
Anyway, all I originally suggested was that since the OP had access to these limestone blocks, and was planning to spend short period of time building a dry stacked oven as an "inexpensive first step towards something more permanent", little would be lost if he gave it a go and it didn't work.

I wasn't suggesting building a fireplace in anyone's house, or pressing burnt lime into bricks or any such nonsense, and I do know the difference between limestone and lime.
Ah, the joys of trying to have a reasoned discussion with the denizens of the internet..

You are missing the point....That lime is only a fractional part of fire mortar. Fire mortar is not 'limestone' when it cures, not any more than concrete is. There is no contradiction...you are comparing apples to oranges.

You seem to have taken the comment about [ not using limestone units for fireboxes etc,etc] out of context. Let's just say that nothing is mentioned about the negative aspects of using limestone blocks to build an oven. Some random reader wants to build an oven, and has some limestone..junky stratified stone that has no business as an oven building unit. Well, lime is in the 'homebrew'....this must be a great stone to build with. Next thing you know, there's a thread about Why did my Oven crumble? An exaggeration, but realistic to some degree....people use this forum as a research tool. I didn't say that because I think you're a moron. But I would say a vast majority of visitors to the forum have little to no masonry knowledge. For example, how many builders on here had any knowledge of masonry or oven building experience prior to reading the Pompeii PDF? The accuracy of the information which is posted on this forum has great importance. True, it's not rocket science, but for a reasonably simple project, there are a bunch of things that can go wrong...from poor building practice to using improper material. Even then, there are builds that fly in the face of 'best practice'. That in itself has a lot of variables. What is available to the builder...what can the builder afford....limitations of the builder etc,etc. And that doesn't mean it's a bad oven, but it does need to come with caveats...in the interest of proper building techniques and using proper materials.

The assumption is made (at least by me) that when most people post about building an oven on here, they don't want to build another. So, applying the best methods possible will yield the best possible result. That's different if they say, it's temporary, I don't care if it lasts. The information still needs to be correct, so someone else doesn't run with it on a 'permanent' oven. That may not sound like people aren't getting credit for knowing better. It's not that....this is a resource. Good info will make it a trusted one.

If I misread your comments, then my bad. Text is almost impossible to convey feelings beyond words...I guess that's what emoticons are for.

[Tscarborough]

Re: limestone vs. brick construction

Best practice would be a calcium aluminate cement. It is refractory. Refractory is technical term with a specific meaning. We talk about things that we can do as individuals on our own projects but that is quite apart from what should be done when being paid by others to perform a service. Professionals should always adhere to and promote best practice.

Best practice does not permit homebrew. Best practice does not allow limestone in fireplaces or ovens.

What you do yourself at your own house does not have to conform to best practice.

edit-- FYI None of the refractory materials I sell contain lime in any form.

[wotavidone]

Re: limestone vs. brick construction

Stone cutter, you may think I'm passive aggressive, but you are just plain aggressive.
I apologise for having an enquiring mind that likes to understand the science behind what we do.

[stonecutter]

Re: limestone vs. brick construction

Stone cutter, you may think I'm passive aggressive, but you are just plain aggressive.
I apologise for having an enquiring mind that likes to understand the science behind what we do.

Well, I'm sorry if it came off that way.

But I'm not sure why you are apologizing for having a desire to understand more, I thought I was clear that that's what we are all here for...a positive interchange of information, ie: good discussion. The replies put up to your earlier posts are referred to as 'nonsense' and then it's implied that you have to put up with some keyboard scholar (my interpretation of denizen), probably won't help continue any positive dialogue. What I'm saying is that you should expect some push back when you post stuff like that.

I have enjoyed some of your posts, like the thread on refractory, and I have no problem dropping this and moving on if you want to talk some more about lime or limestone applications.

[wotavidone]

Re: limestone vs. brick construction

Well, I'm sorry if it came off that way.

But I'm not sure why you are apologizing for having a desire to understand more, I thought I was clear that that's what we are all here for...a positive interchange of information, ie: good discussion. The replies put up to your earlier posts are referred to as 'nonsense' and then it's implied that you have to put up with some keyboard scholar (my interpretation of denizen), probably won't help continue any positive dialogue. What I'm saying is that you should expect some push back when you post stuff like that.

I have enjoyed some of your posts, like the thread on refractory, and I have no problem dropping this and moving on if you want to talk some more about lime or limestone applications.

Denizen is just another word for "citizen".
It was the bit about moulding blocks out of burnt lime I felt was far enough away from what I was asking to make me feel you were being sarcastic.

I think it all comes down to being difficult to communicate when its only the written word with no clues as to tone.

Anyway, truce.

Having read through your posts again, I think I discern the answer to my question. I get the impression that the reason limestone blocks aren't good is because striations of other types of stone cause spalling and cracking, not because it's a case of things getting hot enough to decompose the calcium carbonate to burnt lime.
Is this correct? Because it's wondering about getting hot enough to decompose the calcium carbonate that bothers me.
Here in my town the common advice from the old Greeks and Italians is to use "ordinary brickies mortar with half the cement replaced by lime".
I noticed that one of the pioneers of oven building here has his house for sale.
I reckon his oven would be well over 20 years old. I might go to the open just so I can have a look at it.

[stonecutter]

Re: limestone vs. brick construction

Denizen is just another word for "citizen".
It was the bit about moulding blocks out of burnt lime I felt was far enough away from what I was asking to make me feel you were being sarcastic.

I think it all comes down to being difficult to communicate when its only the written word with no clues as to tone.

Anyway, truce.

Having read through your posts again, I think I discern the answer to my question. I get the impression that the reason limestone blocks aren't good is because striations of other types of stone cause spalling and cracking, not because it's a case of things getting hot enough to decompose the calcium carbonate to burnt lime.
Is this correct? Because it's wondering about getting hot enough to decompose the calcium carbonate that bothers me.
Here in my town the common advice from the old Greeks and Italians is to use "ordinary brickies mortar with half the cement replaced by lime".
I noticed that one of the pioneers of oven building here has his house for sale.
I reckon his oven would be well over 20 years old. I might go to the open just so I can have a look at it.

Sounds good.

The effects of heat on limestone that you listed are some of the problems with using it in general, and especially so in high heat situations, yes. It also has a tendency to heat up very unevenly, which is not uncommon for natural stone, which is usually an amalgam of different minerals. As we all know, that is a major problem for any material, especially when subjected to thermal cycling, because it causes greater stress.

I would say that the lime replacement in the brick mortar is because the masons that recommended that understood the weaknesses of Portland cement.

Also, to your concerns about decomposition of lime in fire mortar.....all mortar degrades eventually. The trick is selecting the right ratios of binders and aggregates to work with the application. In the case of the component (homebrew), all the material has varying tolerance for thermal shock. As mentioned, none of them are true refractory, except the clay...that's why I refer to it as fire mortar...it is only fire resistant. It will degrade eventually, but how fast is relative to the component ratio, how it is mixed and how the oven is used. I would further say that the reason the component mix works well is that the demands on the material are fairly light.

[newhopeclan]

Re: limestone vs. brick construction

Thanks, all, for the great information. I love the passion that a discussion about lime mortar can incite! I am actually an architect, and have a limited familiarity the process of making lime from limestone. I just wasn't sure of the temps involved, etc. I didn't think I would get hot enough to initiate that process, but was mostly concerned about the heat-retaining capacity and the durability of limestone in an oven application. Sounds like everybody agrees that it isn't a great idea. In the end, the limestone was not available when I wanted to start, so I built my oven with solid clay brick that I came by through a friend. I had a great time building it, and now my questions have a lot to do with oven geometry, fire building and cooking techniques, so I think I will start a new post and leave the mortar discussion to the experts!

Thanks again!

[newhopeclan]

Re: limestone vs. brick construction

My final post - here is a photo of my brick oven. My new post will be called "Dry-stack brick pizza oven" if anybody has any interest in helping me make it more efficient.