Can I use Autumn Leaf litter in cob making?

So I am working my rear off raking all these leaves that come into my yard every year. I get to thinking, "what use can these leaves be other than to compost in the back yard?" I have been thinking of building a RMH for some time. I have everything in the house infrastructure that I need, I just need to locate raw materials. I was wondering if anyone has any experience making cob from leaf litter. The leaves that I have will keep piling higher and higher in the compost, and I sure don't mind the nutrient rich soil that they produce, but I am also looking for material that is readily available to create the cob for the RMH. Leaves seem to be plentiful. What do you all think?

Yep, we've tried that. We've built a lot of buildings out of rammed earth and also of lightly rammed earth we call packed earth, maybe it's like cob in formwork. We've been building and living in these houses for 20 years.

The past four years we've been experimenting with insulating materials mixed in, with either our usual mud-building mix, or a high percentage of straw/wood shavings mixed with a good sticky clay that we get from further away. We made one long room with the roof-bearing wall made of the mix packed in forms, and then we've also been making lots of large sort of adobe bricks. So, our experience is that with chopped straw or wood shavings, the result is hard and strong. But with autumn leaves, the result is crumbly.

For the insulating heat riser of a rocket stove, we used straw-mixed cob, and it has been working well for several months.

I think the leaves will be more useful for your compost and soil.

Hi James,

Rebecca has stated it perfectly!!! (excellent job Rebecca!)


Think of it this way James, if something works well in a compost heap...it really won't work well in the wall of a structure, as it just has to much "organic decomposable elements" in its interstitial matrix. This is why we can build a straw bale house, but can't (or at least shouldn't) build a hay bale house.

Good thinking of alternative uses and don't stop asking questions!

Regards,

j

Thanks Rebecca and Jay.

That makes sense. I have since been looking at a few sites where the permies are making briquets and "logs" out of the leaves using a binding agent like flour water. Once dried, they can be used for wood stoves and rocket stoves. Might be something that I try...

Have a great day!

Jamie

Even neglecting the "organic" part of leaves as a cob ingredient, they are the wrong shape to use in any kind of cob that wants to be strong. Straw pieces act as linear strings with the cob gripping at each point; flat leaves act like separators, keeping one part of the cob from interacting with another part. Even in kilns, where any organic matter will be burnt out completely, dried grass clippings work excellently as wet reinforcement and dry insulation, while leaves introduce weakness planes where the kiln wall can slip apart.

I know this is a very old topic, but I just wanted to chime in for people like me who are still looking.

Hay is not more decomposable than straw. Straw does really well in a compost pile.

You don't build hay bale houses because of the moisture content (mold) and the fact that they can spontaneously explode (bigger problem than mold!).

I am curious why straw and not hay is used in cob because hay is much more plentiful where I am (at least organic hay is readily available and organic straw is not) and when the hay is distributed through the mud it won't have those same issues with moisture and spontaneous combustion. I assume it has to do with straw having more structural integrity but I am not sure, which is why I am doing some online sleuthing.

Granted, straw will decompose readily, but it does not have as much nutrition in it as hay, less for fungus or bugs to thrive on. Also, it does not have as many seeds which might sprout while cob is wet. Straw is pretty much just strong hollow tubes, while hay has plenty of flat blades of grass which are weak and a bad shape for strong cob.