Lime mortar & wood ovens?

[Les]

Danny - I did a quick google and found this, looks safe to use lime (whew)

Mortar joints between firebrick in a combustion chamber should never exceed 1/4 inch in width. In fact, a smaller joint is preferred. If traditional sandy mortar is used, it should be a high-lime content mortar that does contain some Portland cement. High-lime content mortars perform well when subjected to repeated episodes of high temperatures.



Les...

[james]

I think the big question is whether a pure air-dried lime mortar will withstand frequent high heat cycles (up and down). I have to admit that I am not experienced with pure lime mortar, but it makes me nervous. With all the energy that goes into constructing the dome, it would be a shame for it to not last. So, voting on the side of caution, I would still add portland.

That said, my experience is limited, and there are different reasons for making a decision -- beyond what is practical and modern. :-)

Jim, Dave or Jeff. Do you guys have some experience here?
James

[barbarian]

like the saying .. do as the romans do or something like that

[Dutchoven]

Trevor
Great question. I am in the process of repointing a structure that was most likely builr with entirely lime/sand mortar. In the research I had to do to complete this task my only concern would be the length of time to set, as you already know. Many possibilities abound in this but I might recommend the use of a small amount of portland/cal-alum cement. The mixture that was recommended to me for this point job referred to a type "O" mortar which is 6-9/2/1...sand/lime/cement...with the addition of 1 to 1 1/2 parts fireclay you might have a really good mix. Maybe even use some fly ash from one of our oven friends near you...could be interesting. Hope Unofornaio catches this thread as well as a few others that are in the masonry trade professionally!
Best
Dutch

[Hendo]

Originally Posted by TrevorML

... 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...

Trevor,

Just as an aside, do you watch "Grand Designs" (ABCTV Thu 6pm). Last week's episode was about a couple building an environmentally friendly house in Wales, and they got the same reaction from builders when they said they wanted to use lime in the render for the outside and inside walls, as well as in the floor slab!

They got there in the end, but not without difficulty. I recall the host saying that the interior had a pleasant acoustic - I took it to mean that the lime render wasn't as 'hard' acoustically as normal plaster, but I'm not absolutely sure about this.

The website at Grand Designs - Carmarthen, from Channel4.com/4Homes is not that informative, but there is a video clip called the “Carmarthen Walkthrough” at Channel4 - Player where you can see the finished result.

Cheers, Paul.

[TrevorML]

Hi Dutch (and James, Les and others)

if your wall already uses lime mortar I personally would stick to pure lime mortar as I have seen real life examples and somewhere on the net where the use of cement in mortar has led to VERY serious degradation of the surrounding material do to the impervious nature of cement retaining all of the moisture in the brick/stone leading to the material basically just rotting away... will see if I can find a link to some on the net...

the setting time is not too much to worry about really... the original builders built the building with it and it was fine and is still standing... the long setting time refers more to the complete set when the full chemical process has taken place... I could easily walk on my paving the next day with no problem and the render could be touched... altho could scratch it for a couple of weeks but now it like stone...

infact when laying bricks... the mortar sets very firm within minutes it seems but remains damp and fragile only if knocked until the next day or so...

I was hesitant at first until I kept on reminding myself that in the order of 3 - 4000 years of continuous use is not too bad a track record in the use of lime mortar... how long has portland cement been around... 150 yrs and only about 70 to any scale... sort of speaks for itself really

same issue with mud brick and pise... the critics say it is not strong enough to stand up to the ravages of time, weather etc etc... but there are examples that are 2000 years old still standing and still in use... what is important is HOW it is used and the detailing used in it's use... not the material itself

the uptake of cement has more to do with politics and business and money rather than the inadequacies of the materials themselves... cement enabled faster construction of thinner walled building techniques which meant that the builder could be in and out of a site quicker and with less of a cost to him in materials and labour... the typical trend with all of the 20th cent processes... seems to have been the dawn of the age of the accountant, and the bottom dollar, in all decision making processes... environmental and people issues just did not register at all... obviously there were other issues at play as well... the Great Depression... the lack of materials after the 2 big wars... etc etc... but the bottom dollar approach had a very big part to play in it

this whole attitude towards cost and the lack of consideration for the environment plays throughout so many areas... paint manufacture, cabinetry etc... where big business dominates the initiation of processes that are followed... I remember reading a long time ago about a paint company employee going to one of the Shaker communities and in a "display" house sneaking a sample of the paint from the walls only to go back to the lab and reverse engineer the samples to work out the original recipes and then patent them... not for the betterment of mankind and building practices in general... but to shelf the recipe so no one could ever use it commercially... as it lasted FAR TOOOOOO LONG !!!! hence less dollars for the business community... whereas these recipes used originally were not held in monopoly but freely available for all

this is not about any luddite principles at work... just a respect for the environment and people...

there is my soapbox for the day... I can see this is going to be one of those days at work... I can just see it...

but it would be good to have some knowledge chime in on the use of pure lime mortar use in wood ovens

cheers
Trevor

[TrevorML]

Hi Paul

I do watch Grand Designs... but unfortunately we missed last weeks episode!!! and was most peeved when we realised and did not tape it!!!... is always the way that the one you miss is the most relevant

thanks for the link to the episode... must see if Borders or ABC has the DVDs

have you built your oven yet?

cheers
Trevor

[Dutchoven]

Trevor,
Your point is very good. In my research I ended up speaking with a representative from the International Masonry Institute(he was a specialist in repointing brickwork and restorative brickwork), he is the person who ultimately recommended the very small amount of portland cement in the mixture. Many areas on our building had been patched with a straight portland mortar and the trapping of moisture created the most problems. Even with a small amount of portland the mortar mixture we ended up using is quite soft even after now almost 5 weeks since we began the project as compared to portland cement mortars after only a few days.
Thanks for caring.
Trevor are you in the masonry trade?...or some other building trade?
Best
Dutch

[TrevorML]

Hi Dutch

not directly in the building trade... long story short... in University student admin currently but trained as an architect and after some years doing contract and freelance work ended up via a weird route in the Uni's admin... so now my training is just put to use in home reno's and continuing my love for responsible architecture and building

cheers T

[asudavew]

seriously..........

we live in a new time and day

give up your concrete floors, hallways, and streets, walk somewhere else


I don't think a bit of cement will ruin the world.

But if you are convinced to build with lime
then build.

I look forward to your success.