Quick Answer
To install formwork for rammed earth walls, use a sturdy, well-drained frame, level it with a spirit level, and secure it with stakes and strings. Ensure the formwork is at least 1 inch (2.5 cm) higher than the desired wall height to account for the soil mix settling. Compact the soil mix in 2-3 inch (5-7.5 cm) layers to achieve the desired density.
Designing the Formwork
Designing the formwork is a critical step in building rammed earth walls. The formwork should be sturdy enough to withstand the weight of the soil mix and the tamping process. Use a durable material such as plywood or oriented strand board (OSB) for the formwork, and ensure it is well-drained to prevent water from accumulating in the soil mix. The formwork should also be designed to allow for easy removal after the soil mix has been compacted.
Building the Formwork
To build the formwork, start by creating a level base using stakes and strings. The base should be at least 1 inch (2.5 cm) higher than the desired wall height to account for the soil mix settling. Once the base is secure, attach the formwork panels to the stakes using screws or nails. Ensure the formwork is level and plumb throughout, using a spirit level to check the alignment. Use stakes and strings to secure the formwork to the ground, making sure it is tightly secured to prevent movement during the tamping process.
Compacting the Soil Mix
To compact the soil mix, use a hand tamper or a mechanical tamper, depending on the size of the wall. Start by compacting the soil mix in 2-3 inch (5-7.5 cm) layers, using a gentle tamping motion to avoid compacting the soil too tightly. Continue compacting the soil mix until the desired density is achieved, typically 90-95% of the soil’s maximum density. This will help to achieve the optimal thermal mass and structural integrity of the rammed earth wall.
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