There are many ways to build a wall. Compacting a mixture of local soil and cement against wood formwork is certainly not the easiest. Throw 4 inches of insulation and a whole bunch of rebar into the middle of an 18″ rammed earth wall and it’ll satisfy the building inspector, but it takes a full team mixing and ramming, constant inspection for bulges and blowouts, and a whole lot of patience to get it right.
We’re figuring out this system of structural insulated rammed earth on the fly. Of course we had a big head start with the help of our friends Brad and Roger from Earth Wall Builders. It’s a modern take on traditional rammed earth that EWB has mastered. Rather than relying on clay as a binder, we use a mixture of local material composed of sand and silt to larger aggregates, add in a bit of portland cement (significantly less than concrete), and some concrete pigment for a richer color and wet it just enough for it to hold together. It goes into the hand built formwork along with rebar and rigid foam insulation and is compressed with pneumatic rammers and then hand tamped to ensure a good surface finish and adhesion to the rebar. The process is tedious, especially in building formwork, but as one of the stars of this project, these rammed earth walls deserve all of the time that we are putting into them.
So why rammed earth? Well, it’s particularly appropriate for Southern Utah for a couple of reasons. We can use more local materials and cut down on materials like Portland Cement with high embodied energy. Then when we strip the forms, we have an entirely finished wall, inside and out with no need to add drywall or any other finish material. The red sand makes for a great base material for the walls, and the desert climate with little precipitation means less surface erosion over time. A mild winter also allows us to build in February with less risk of our walls freezing. And then of course the finished walls are very much a product of the intensive process that it takes to build them, showing each layer of material and telling a story about its conception that a stud wall just can’t.
Ed Abbey (who actually hung around Bluff, Utah in his time) once said something like: “There is no shortage of water in the desert but exactly the right amount, a perfect ratio of water to rock, water to sand.” The same could be said for a carefully built rammed earth wall.
- Jared and Shay