Lime mortar & wood ovens?

[TrevorML]

Hi good folks

some time ago while renovating my house I discovered the joys and environmental benefits of using lime mortar for construction... I then got to thinking when preparing for my Pompeii oven if it is at all possible to use lime mortar in it's construction... especially considering that cement based mortars have only been around since ~1860's and only used widely since ~1920's/30's when it replaced lime almost totally... so all pre-1860's ovens surely would have used lime or hydraulic lime mortar exclusively

if anyone has ANY info on this I would be most pleased to hear from them

cheers
Trevor

[Mojoe]

Here's a little tidbit: Cement - Wikipedia, the free encyclopedia

[TrevorML]

Thanks Mojoe... I was aware of that one.. good ol' wikipedia is always a first port of call... I should have been more specific... I am trying to see if it is possible to use non-Portland based cement as I would like if possible to use a pure lime/sand mortar without the addition of Portland cement

cheers
T

[Mojoe]

Ah, I see... less history and more field experience. Just from briefly scanning the net it appears to be a suitable alternative. Hopefully someone will respond with the insight you seek.

[james]

Hey Trevor,

Where are you looking to use your lime mortar in your oven project? I am working with lime plaster for internal wall finish in our house, and for the enclosure for our new outdoor kitchen.

In general, portland or calcium aluminate based mortars work well for the construction of the oven chamber itself. They set and cure to a hard material that can (in varying degrees) withstand the heat and thermal cycling that a brick oven undergoes. You try to minimize your joints, to make the mortar less "mission critical."

I would be very interested in learning more about Lime, and how it sets.
James

[TrevorML]

Hi James

a reasonable why use lime link...

the lime cycle...

the British Lime Assoc has great info...

a great little illustration of the lime cycle...

yet another good site...

I have used lime for wall rendering and for bedding/grouting sandstone paving tiles... it is a fantastic, very forgiving material... don't have to worry about it setting on you if you mix up too much... just keep it wet... can leave it covered for work the next day or even days down the track... just keep it wet/moist as it sets through drying and the uptake of CO2 from the air that it released in it's manufacture (a part of the lime cycle)... I have used commercial lime putty fro the only supplier here in Oz and made my own from hydrated lime powder and both seem to work fine...

when I was first time going to make my own putty from the hydrated lime I was enquiring from a building supply place... run by an Italian family so thought they would know all about lime... to work out quanities etc and when he learnt of my using a mix of just lime, sand and water for my wall render he was totally aghast...

"you can't do that... it will all fall off!!!"

no... I said... it doesn't as I had already done it with a lime putty, sand mix with NO portland cement at all... and why do they put lime in mortar... because it makes it "sticky" and VERY workable!!!!

lime mortar is a fantastic thing to work with... and fully recyclable... old lime mortar can easily be scraped off of old bricks etc... easily crushed without anywhere near the same energy required to crush concrete/cement based products and then reused in the next lot of lime mortar...

basically... it starts out as limestone... is burnt and releases CO2... etc etc.. then takes back CO2 from the environment to set... and in the process returns to being limestone.... it breathes... caustic BUT non-toxic...

HENCE... my desire to find out if it is OK in the making of wood-fired ovens... especially since surely all ovens would have been built with lime or hydraulic lime until near mid-1900's

cheers
T

[james]

Where does Pozzolan fit in here? I always thought the Romans mixed pozzalan with lime to make a mortar that would set through a chemical reaction. That is how they made some of their serious marinas and other major construction projects. Is that how that made their brick ovens? I have asked various Pompeii experts, but never found anyone who could answer.

As an aside, did Pozzolan stop being used in the middle ages? Stone construction fell back, and was replaced by more "rustic" wooden structures in many places. Still, brick ovens were built at the time, and some are still standing. Something must have gone right.

What was the heat resistant mortar they used?

Hmmmmm.
James

[james]

One more thing. Thanks for the Lime cycle graphic. Nice.
James

[barbarian]

I just watched a show yesterday about Roman structures and yes they indeed used lime made from crushed lime stone pozzolan ash (1:2 ratio) and water not only as mortar but also for casting very large objects..I have to say it was pretty amazing to see the chemical reaction the lime made with the water then make a mold and drop it underwater to set
I can see substituting pozzolan ash with fly ash which according to this story causes a similar chemical reaction as pozzolan ash
http://www.djc.com/news/co/11133038.html

Originally Posted by james

Where does Pozzolan fit in here? I always thought the Romans mixed pozzalan with lime to make a mortar that would set through a chemical reaction. That is how they made some of their serious marinas and other major construction projects. Is that how that made their brick ovens? I have asked various Pompeii experts, but never found anyone who could answer.

As an aside, did Pozzolan stop being used in the middle ages? Stone construction fell back, and was replaced by more "rustic" wooden structures in many places. Still, brick ovens were built at the time, and some are still standing. Something must have gone right.

What was the heat resistant mortar they used?

Hmmmmm.
James

[Dannyboyblue]

Interesting thread here.
I love the idea of being as traditional as possible in oven construction.
It seems to comes down to how the lime mortar reacts to the heat.

The Building Limes Forum (thanks for that link, Trevor) says
''12. The use of lime has ecological benefits
Lime stone can be burnt at relatively low temperatures to achieve full calcinations. Kilns need to reach 900 to 1,000ºC as opposed to 1,300 to 1,400 for OPC. Free lime absorbs carbon dioxide in the setting process of carbonation. It is possible to produce lime locally on a small scale and if this is done the consequent reduction in long distance transport also has ecological benefits."

So would the high heat of a pizza oven make the lime unstable in the lime cycle with its continued refiring?

Any one know?