limestone vs. brick construction

[newhopeclan]

I am planning to build a dry-stack pizza oven in my back yard as a first inexpensive step toward something a little more permanent. This link shows the general level of complexity / design of my oven:

http://www.westernexplorers.us/A_sim..._bake_oven.pdf

I am just starting to research my project, and have a fundamental question. I have access to a pretty decent quantity of modular limestone (similar size as brick) that was originally used as cladding on a home. The actual floor of the oven will be firebrick, but assuming I can get the joints tight, would limestone be an appropriate material for the walls and roof?

I don't see a lot of dry-stack ovens on this blog, so if there is another more appropriate site, feel free to point me in the right direction.

As for actually using the oven, I find some resources that say to remove the embers and all coals/soot before baking, while others leave them in. When is one appropriate vs. the other?


Thanks in advance for your help!

Mike

[Toomulla]

Re: limestone vs. brick construction

Looking forward to the responses as I thought you burnt limestone and wood in a kiln to make lime but don't know the temps involved

[wotavidone]

Re: limestone vs. brick construction

Looking forward to the responses as I thought you burnt limestone and wood in a kiln to make lime but don't know the temps involved

You need a minimum of 900 Centigrade to decompose the carbonate. Unlikely (but not impossible) to achieve this in a wood oven. In a dry stacked oven where expense is a concern, I'd certainly be trying it. If it doesn't work nothing much is lost.
I reckon you'd need real bricks for the floor. The coals sit on that, and wherever there is a localised hot-spot you may damage that area if it's just limestone. Marble floors fail, apparently, and marble is recrystallised carbonates.
So floor no, dome maybe, if it's a dry stacked oven where little is lost if it fails. I'm all in favour of experiments that further the knowledge, as long as the loss on failure is low for the experimenter.

As for actually using the oven, I find some resources that say to remove the embers and all coals/soot before baking, while others leave them in. When is one appropriate vs. the other?


Thanks in advance for your help!

Mike

One tends to leave the fire in (swept to one side) to maintain high temps when cooking pizzas, and clear it out when baking bread. For roasts, a small fire might help, or might not be necessary, depending on how much thermal mass you have and how much you loaded it with heat.

[wotavidone]

Re: limestone vs. brick construction

A postscript - I just read the linked PDF. I would say that oven will probably not acheive temperatures high enough to decompose limestone. I'd certainly give that a try - especially if those limestone blocks are free

[wotavidone]

Re: limestone vs. brick construction

PPS, that oven is a little too simple. You should at least overlap the bricks in the corners so the side walls are tied to the back wall.
Wouldn't be good if the whole lot fell over while you had the fire going.

[Tscarborough]

Re: limestone vs. brick construction

Trust me, limestone will not last long in a fireplace/firepit, much less an oven.

[wotavidone]

Re: limestone vs. brick construction

Trust me, limestone will not last long in a fireplace/firepit, much less an oven.

Sounds like it ain't such a good idea. Maybe just settle for any fired clay bricks you can get hold of.

[Toomulla]

Re: limestone vs. brick construction

Trust me, limestone will not last long in a fireplace/firepit, much less an oven.

You could use the lime to mix grog for the replacement brick oven

[wotavidone]

Re: limestone vs. brick construction

Trust me, limestone will not last long in a fireplace/firepit, much less an oven.

It's all very confusing.

On the one hand, we put lime in the mortar, expecting the lime (calcium hydroxide) will carbonate and turn back into limestone (calcium carbonate), thus providing the strength after the Portland Cement breaks down.

On the other hand, we say don't use limestone (calcium carbonate) for the oven as the heat will break it down.

It's all too hard, think I'll go light the oven and cook something to take my mind off this conundrum.

[Tscarborough]

Re: limestone vs. brick construction

Limestone is not lime.

[Toomulla]

Re: limestone vs. brick construction

I would like to hear from stonecutter, I understood that lime was added to a Portland cement mortar to improve workability and offered some self healing of shrinkage and other small cracks via the lime dissolving and recrystallising there seems to be some idea that it makes the mortar flexible there is no such thing as flexible cement to my knowledge

[Tscarborough]

Re: limestone vs. brick construction

As I said, lime is not limestone. Lime is added to mortar for several reasons, and in fact lime mortar with no portland cement is often a better choice than a portland cement/lime mortar (PCL).

Mortar is not "flexible" per se, it has a modulus of elasticity (MOE) measured by flexural strength. "Strong" or "hard" mortars made with a high ratio of portland cement and no lime have a low MOE, while lime mortars and PCL mortars have a higher MOE. High lime mortars also are capable of autogenous healing, while portland cement does not have this property.

[Tscarborough]

Re: limestone vs. brick construction

Note also that autogenous healing takes place on a microscopic scale, not a macroscopic one. That is, if you can see a crack, it ain't gonna heal itself, no matter what the composition of the mortar is.

[stonecutter]

Re: limestone vs. brick construction

I'm not sure I can add much to what's already been said. The most important parts of this discussion are these:

Limestone is not a suitable material to build an oven with.

Limestone is not the same as type S or NHL used for mortar.

Tom and I could probably turn this into a 20 page thread about lime and limestone. In the end, all the info is out there, and let the builder use discretion.

[stonecutter]

Re: limestone vs. brick construction

I would like to hear from stonecutter, I understood that lime was added to a Portland cement mortar to improve workability and offered some self healing of shrinkage and other small cracks via the lime dissolving and recrystallising there seems to be some idea that it makes the mortar flexible there is no such thing as flexible cement to my knowledge

I will touch on this a bit, and say that numerous study's have shown lime mortar to be superior to opc based mortar in many ways. When opc is added to lime, the mortar has a higher compressive strength, but comes at a cost... Breathability and tensile strength...that being relative to masonry. There is a ton of information out there about opc and lime mortar...it's not really that critical to small scale projects like what you see on the forum.

The main focus should be on the material used for building, with what type of mortar a close second...and there is a lot of forgiveness in that area