Quick Answer
Most Effective Plastering Methods for Earthbags: A combination of lime-based plasters, such as lime putty and hydrated lime, and natural cements like slaked lime and gypsum can be applied to earthbag structures. A mixture of 1 part lime putty, 1 part sand, and 0.5 part hydrated lime provides a durable and breathable finish.
Choosing the Right Plaster Mix
When selecting a plaster mix for earthbag structures, it’s essential to consider factors like durability, breathability, and ease of application. A mix with high lime content (around 50-60%) is ideal for earthbags, as it allows for good adhesion to the polypropylene material and provides resistance to moisture and erosion. However, a high-lime mix can be slow-drying and prone to shrinkage, so it’s crucial to apply multiple thin coats to avoid cracking.
Applying the Plaster Mix
To apply the plaster mix, start by roughening the earthbag surface with a wire brush to create a bond between the bags and the plaster. Then, mix the plaster ingredients according to the recipe and apply the first coat, using a trowel or a brush to spread it evenly. Allow the first coat to dry completely before applying subsequent coats, following a 24-48 hour drying cycle between applications. A general rule of thumb is to apply three coats, with each coat consisting of around 1/8 inch (3-4 mm) of material.
Finishing the Surface
Once the final coat has dried, use a sanding block or a sanding sponge to smooth out the surface, removing any imperfections or bumps. For a more durable finish, consider applying a thin layer of a natural sealant, such as beeswax or plant-based oils, to protect the plaster from the elements. This step should be done with caution, as excessive sealing can compromise the breathability of the structure.
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