Rammed Cob/using Pine needles?

Hello fellow homesteaders!
Recently I've been conducting research and experiments on all earth building related and as I don't want to bore you with the theatrics of the whole process -I'll get straight to the point.

One question I have for you guys is can cob be rammed to make a stirdy wall? Some will say it wouldn't seem strong enough hopelessly comparing it to the original materials such as sand,cement, and clay in rammed earth but as I see it- Rammed earth is just another type of adobe(using cob made with straw,clay,water,etc) If I'm doing the same process in pressing cob (with the assuption Im building a cob home) isn't that the same as rammed earth?

Secondly - I've made plenty of test bricks in which one had no straw (turned out brittle and more easily crackable); the second was with pine needles, so it was still absent of straw( in which Im starting to believe pine needles just isn't the same because th e difference in the strength of the pine needles is very hard to form into cob balls for the form and the strength of pine needles isn't needed and just gets in the way of binding the materials). And lastly I've made a cob model with pine needles which it turned to rock like the others but as soon as it rained it was stirdy a little but also flimsy. I recycled the earth back to its original place in fustration and I'm hoping ....just hoping regular grass straw or mulch is the answer to my problem.

On a side note , where I live has plenty of red clay, and I use topsoil sand to form the cob which seems to work but If I could get an opinion on my organic material I've been incorporating that would ease me a great lot.

If cob is done right it has no voids so ramming it further will not make it more stable.

The big factors that make cob as stable as can be are the quality of the sand and the fiber enforcement.

The sand needs to be sharp. This makes the cob strong.

The fibers need to be strong, long and bind well to the sand and clay. This makes the cob tough.

Pine needles are definitely not long enough for this.

I would expect the best outcome with recycled twine at 1-2 foot in size - longer could be getting harder to mix.
Straw is in my case the preferred material because it is a lot cheaper and works good enough.

Thank you for reminding me that I need to make more tests and start doing the models homes I planed.

I Ben...welcome to Permies...

As stated already...Ramming and Cobb work is not really the same thing. Cobbs...or earth/clay matrix...are worked damp to wet...most rammed earth matrix are worked very dry and in forms. Now where there is "cross-over" is in "light straw clay" or "light woodchip clay" infill methods that are rammed and do use forms. Earth matrix building has countless forms and fashions from around the globe, from massive pure clay without adulteration of any kind (pure clay) to those types with all manner of amalgamation and additive. As for strength, many forms would give OPC (ordinary portland cements) a run for their money in the way of strength and durability in compression. OPC in general is not a very "permaculturist" based medium, so many of us do not promote or chose to use it in the industrial format and rely instead on limes, and perhaps geopolymers as they are becoming better understood.

Even though many species of Pinus around the globe are more than long enough to act as a "botanical fiber additive" they are entirely too brittle in nature after being dried to give much strength. There are those that have used some species with limited success so if I was faced with an abundance of them and clay...I would make "test brick" (that are aged at least 6 months) and compare them to some of the other available fiber material at hand. Adding just a soil to the mix is not advisable at all. anything added to an earth matrix for building must be in the purest form possible and have a specific reason for being there otherwise the mix is just "mud" and will definitely need an armature to have structural integrity.

Fiber lengths vary in the many different modalities. Most are from 30 mm to 100 mm in length. When a method employs a longer form, 300 mm to over a meter, they are "laid in place by hand" at each stratum course, and act more like bridging for that stratum. I am not a proponent of "free cobbing" and probably never will be in most applications accepting for limited structural sizes (ovens, tiny structures, and the like.) I tend to lean toward and only recommend "infill systems" and none structural "earth work," unless that "earth work" (cobbing) is of a massive form, where the wall diaphragm structures are greater than 600mm in thickness or more, with excellent small and large fiber bridging and tying throughout the matrix.

Hope that helps...good luck and keep asking questions and experimenting!

First off! thanks for the swift reply. It really helped alot in deteriorating any prolonged horrific months work of testing. Which concludes if you don't know the basics of the materials and the knowledge of fundamentals your gonna need alot of tissue.
You're also welcome jay C. Im drawing up a few pictures myself on how to go about the architecture. The pine needles get the boot in this situation.

I'm starting to realize and get a real picture in my head of cliffs, and how the materials works like roots. Non-cut ( all my experiments except # 2 resulting in a stable brick rock/pine adobe in mind ). I digged a small hole, cut some top-soil, and shifted the rocks- which magically appeared back in the mud upon being rained on some how? if you can imagine this is the worst part of the process through normal means labor intensive wise.The tension of downward compression was all go but the bending and twisting pressure gave out. Only to have my experiment and dreams crumble before me in the bare hands of my friend, even though it was a kind of a struggle involved. Which steamed me as I replied to my friend "it's not supposed to be thrown around and beatin' to a bloody pulp"."It's supposed to sit harmlessly and harmononically ontop of eachother's unit's". The pine tendons could be seen in the adobe but not nearly enough pine nor the the fact the absents of straw held the adobe formed together.

My cob sculpting skills are average compared to the results I was given( so a full cob wall is out of the picture for me probably and Im keen on the pattern of adobe but stacking arches, dome making, mud roof crafting, earthen floors or even starting a course are a little vague to my ideology. The test for these bricks were in a timely manner about 2 or 3 days and then it would rain before I check the results.

I'm not sure what to call it but we built several buildings in what might be called rammed cob back in the 90s and they are still going strong. Yes, when we've needed to make a hole in one of these walls, you could describe it as "it gives portland cement a run for its money."

We always called it rammed earth, until the designer, a local Ladakhi engineer and activist, went and studied rammed earth in France and learned that real rammed earth is much sandier and much drier. Then we thought we should stop calling our old method rammed earth and started calling it packed earth, but rammed cob would also be a good name.

How we made our walls was, we would test some ratios of the sandy soil of the site mixed with some clay from not too far away, by making adobes of the different mixes and stamping them in well. Then we'd dry the adobes and make sure they don't crack from shrinking (ie enough sand), and how they react to being kicked or dropped (ie enough clay). So we made simple forms of planks about 1 to 2 feet tall, packed this mix in and rammed it as hard as we could with hand stampers, let it dry a day or two, moved the form over to a new spot, and after a few days moved the form on top of the recently built stuff. It has been very strong, and we have no worries about that. We used arched earthen wood-free lintels the first year because of a delay in wood delivery, so the next year we tried breaking one out to replace it, but the arch was so strong, "giving concrete a run for its money," that it took strong guys with sledge hammers to chip it away. So we went ahead and built the whole building and some small outbuildings with it. When the designer went years later to study modern rammed earth, he took samples of our clay to the lab and discovered that it was actually fine silt, not clay. And yet the structures are very strong and good. When we need to break them down, either you have to chip away, or if you can push it over, it comes down in big solid chunks that crash on the ground and sit there like boulders.

We didn't use any biomass such as straw in these buildings,because as you can see in the backgrounds of the photos, there's a real shortage of biomass in ladakh. Later when we did vaulted roofs over a 5 or 7 foot span, we did put some thorn bushes in as binding but I'm not sure it helps or hurts, but those vaulted roofs are also strong enough. Same material -- wetter and with more clay (actually fine silt) than proper rammed earth.

Silt in general is to be avoided...as you can see however...some forms are very unique and actually have the characteristics of a "pozzolanic" like you may find in a natural concrete...Above could well be a form of that...and these are also a foundational element of "geopolymers."

That was an excellent post Rebecca!

Thank you, Jay!

Yes, that silt is really claylike. We have always used it for claymodeling: just for fun, not fired or anything, and we never thought it wasn't clay, as the objects dry and keep their shape just like clay. So it's not just ordinary silt that would be bad for earth building.

You know...you may have something unique there...

If you can ever find a way for an in depth analysis of the elements in the silt, it may turn out to be one of (or several) elements in natural concrete. These do present as a "clayey silt" in some forms. That could have some pretty far reaching positive economic importance to the local community.

Regards,

j

Those buildings look awesome man and well constructed , it's with these pictures I have a finer idea of how to create a second story in the house (thanks alot).
Yes, I tried searching around for different names with "also known as" others coming close to being called" poured earth , cast earth, just all different confusing names although I have alot more to work with earth building now upon discoveries.

Rammed earth's reputation for a strong structure with sand and cement put me off ease at first but thanks to you guys , I know I wasn't the only one with this idea in mind. As of right now I'm trying to figure out the roof and the floor structural engineering- I know it's a million ways to finish it but the structures daunting on scarcity from my current knowledge(wood or bamboo). Soon I hope on crafting another adobe test, drafting and creating a prototype of the house-So when I use straw I hope it's a little easier to sculpt and play with. Anybody else have trouble with making the worm test? -It has to be the lack of sand now that I think about it.It's a silly question on the surface but that bases should allow for good sculpting craftsmanship and finer details.