Rammed earth is having a moment in the magazines, mostly in places where it does not rain sideways for a week. Quarry Steading is in Glen Clova, where it does. This is what four years of that wall have taught me.
The mix is the site
We dug a test pit in the field behind the ruin and sent the subsoil to a lab, then ignored the lab and did the jar test in the kitchen: shake the soil in water, let it settle, and read the layers of sand, silt and clay like strata. The Clova soil came out at roughly 28 per cent clay, which is too sticky on its own, so we blended it two to one with the crushed stone that was left over from rebuilding the gables.
Every batch was rammed in 150 mm lifts inside plywood shuttering that we made ourselves. You can see the lifts in the finished wall, a faint band every hand's width, and the client has stopped apologising for them to visitors because the visitors like them.
Weather
Three things keep the wall dry: a wide overhang, a high plinth of stone, and a lime render on the weather face. The render is the one people argue about, because a bare earth wall is beautiful, but on the west side of a Scottish glen a bare earth wall is a slow puddle. We left the inside faces raw and the east face raw, and rendered the rest. Four winters in, the rendered faces are fine and the raw east face has weathered back about 3 mm, which is what the books said it would.
What I would do differently
- Order the shuttering ply thicker. Ours bowed on the long wall and the bulge is still there.
- Ram the window reveals with a timber former rather than cutting them afterwards.
- Build the sample block in October, not April, so it sees a winter before the real wall does.
The children in that house sleep in the earth rooms by choice. That is the only performance test I trust completely.
