Building RE in Africa
House plans are in a bit of a lull these days as I focus on guesthouse and greenhouse, and, on fixing tractor. We’re going to move a bunch of dirt this summer, so a tractor with brakes will be useful.
I’ve also, though, been reading up on converting dirt into rock hard walls. Rammed Earth (RE) is magical that way – if, that is, a lot of labour is added. I’m reading to learn more details about RE so we can more accurately lay down the foundation this year.
Did you know that clay particles are tiny discs? When we mix jagged edged sand and gravel with clay and silt, add just the right amount of water, and then pound the mixture into a form, the clay discs slither into all the spaces between the jagged bits and bind it all together. It’s important that the moisture content of the mix just barely allows for this fluidity of clay particle movement.
We’re fortunate that the proportions of the hill we’re converting into wall are nearly perfect. I did the soil-mixed-with-water-in-a-jar test last year and found that we have about 70% sand/gravel and 30% clay/silt. What I didn’t know at the time, though, is that we need to ensure we have the RIGHT kind of clay. We’ll do that additional test once we have a softer hill to work with. Here’s hoping it isn’t bentonite. Bentonite clay expands when it absorbs moisture – which isn’t great for earthen walls.
In South Africa, back in the 80s, we built a rammed earth home with 8 inch thick walls. We used homemade tampers and did all the pounding by hand. That house was not built into a hill and we weren’t concerned with insulation in that climate. The way RE is done in cold climates is with Styrofoam insulation sandwiched between two earthen walls. There will be an 8 ” inside wall, then 4 inches of insulation and an 8 ” outer wall. That’s a lot of dirt and a lot of pounding. For now, what we need to know is that the foundation will be about 24 ” wide to accommodate this wall.
The plan is to transform what is abundant into a more or less permanent dwelling – but that in eras to come, if the house needs to return to the hill, it can do so with grace.
Can we build RE on top of a tamped rubble-rock filled trench? Or do we need a reinforced concrete foundation? We’ll look into that over the next couple weeks.
Best. David and Maggie.