For the month of August, our fellows embarked on a special build project: creating a Cob Bench in the Verde Partnership Garden at Verde Elementary School in North Richmond. This project combined hands-on learning (including a deeper dive into soil textures), teamwork, and traditional building methods using natural materials.
Here’s a summary of the process and learning journey:
- The VPG team selected the bench location near their garden beds, activating the space as an additional breakout and teaching area.
- The team cleared the area by weeding and removing large plant matter.
- With Adam’s support, they staked out a crescent shape using rope and measurements to guide the bench’s size.
- A trench was dug and backfilled with drain rock to prevent flooding during the rainy season.
- Guided by the VPG team, clay soil was harvested directly from the ground, followed by soil ribbon tests to confirm clay matter.
- The cob mix was prepared: a 2:1 ratio of clay soil to sand, blended with water and stomped, then reinforced with about 10% straw for strength and stability.
- “Slip” (a clay and water paste) was made to coat the cinder blocks, giving the cob something to bind onto.
- The first layer of cob was applied. The next day, cracking was observed, so the team repeated the cycle—mixing, stomping, and applying—building strength layer by layer (about 3–4 rounds). They discovered the best mix for their soil was closer to a 1:1 ratio of clay soil to sand, with more water and straw.
- After two weeks of curing, a lime plaster base coat was applied: 2–3 parts play sand to 1 part Type-S lime, with water as needed.
- The final layer of Lime Putty with Pigment was added: 1 part Type-S lime to ¾ part water (as needed) plus a full bag of mineral pigment. A second round with more pigment was applied later to adjust for too much lime in the initial mix.