Rammed earth recipe?

Hello Permies,

We were planning to do a big project in our house, since we found this forum we feel so inspired to build naturally. We would love to build our kitchen island walls from rammed earth.  They say mostly the recipe is 25% clay and 5% concrete and the rest sand.
We did an earth test and it looks like it has around 43% sand, 55% silt and 2% clay. Im trying to find the right recipe for rammed earth for our ground online but I can't find much about the silt part.
Somwere I red that it should consist of 25% silt/clay. But can you count silt as a clay? Doesn't it need more clay than only 2%?

Thank you so much with helping!

The best way is to try it out.

Make a block of it in a makeshift press of some kind, like two nesting buckets whose sides and bottoms won't give out. I would stand the buckets on a flat, hard surface, and find something unyielding that will fit the inside of the inner bucket to keep it from bulging up.

Then mix up your rammed earth mixture, place it in the bottom of the bottom bucket, place the top bucket atop it with the reinforcing metal plate/paver/rock/whatever, and then either get inside and jump up and down on it, or find another way of applying pressure.

You can then take the resulting cylinder out (I would grease the bucket like a pan before you load it with earth to facilitate this), and subject it to any standard masonry tests. You will find out in short order whether or not your recipe worked.

I admire your enthusiasm for rammed earth, but the wall thickness is typically much more than what you'd find on kitchen island walls. An alternative to this that would result in much more interior storage space would be to build an island structure and prepare it as a matrix onto which you can apply cob. You don't need masonry to support a kitchen island.

But let us know what you decide, and good luck.

-CK

Hello Chris, thank you much for helping! yes that is actually the best idea. Just try it out ourselfes. Ill post about  the recipe if it will be good. We got the idea of rammed eart because we want to incoperate a rocket stove in the island and we red the material is great as a heat battery too.

Kind greetings from Netherlands

I agree that you will lose a lot of space, but maybe you aren't concerned about the space and just want a particular look/feel, a heat sink or a structure to moderate humidity or temperature.

Anyway, compressed earth blocks is something I really want to try and one unexpected thing I have heard mentioned is to avoid clays that expand when wet since they can cause blocks to self destruct rather quickly. In your case, it might actually not matter as much though since it would be indoors and presumably better protected from moisture.

One rammed earth company is basically doing an engineered sandstone that appears to me to contain little to no clay. I doubt that it has quite the same ability to transfer moisture and to cool without the clay, but might be very appropriate for your use case if you can figure it out.

The image doesn't seem to work. But I did some experiments, with sand, without sand, with less concrete and more but the samples all broke after drying. So this recipe doesn't work. It's a good point to think about clays that will not expand much. Now Ill be back to the idea to just recycle old brick (thats also used in the building plan). Still very interested in trying rammed earth, so if ill get to try a new recipe ill keep you posted.

Kind greetings

I think you mean 'cement' not concrete as part of the mixture.

Its important to get it correct in the first place.
Cement as an additive to concrete.
Sometimes lime can be used as an alternative.
I think you should look at cob instead it will make narrower walls, but by experimenting you
may be get something that works.