Is it necessary to plaster exterior rammed earth walls for protection?

Weather Resistance

Rammed earth walls are highly susceptible to weathering and erosion, particularly in areas with intense sunlight, high winds, or heavy rainfall. Plastering the exterior walls with a breathable, water-resistant plaster such as lime or clay can help to protect the rammed earth from water damage, salt crystallization, and erosion. A 1-2 cm thick layer of plaster is typically sufficient to provide adequate protection.

Insulation and Thermal Mass

While plastering can help to protect the exterior walls, it can also reduce the thermal mass of the rammed earth. Rammed earth walls gain and release heat slowly due to their high density and thermal mass, which can help to regulate the indoor temperature. To minimize the impact of plastering on thermal mass, it’s essential to use a thin layer of plaster and to ensure that the plaster is not sealed or painted, allowing for airflow and moisture transfer.

Formwork and Soil Mix Considerations

In arid and desert climates, where the risk of water damage is low, plastering may not be necessary. However, it’s still essential to use a water-resistant soil mix and to design the formwork to minimize the risk of water seepage. A 1:3 or 1:4 mix of soil to sand is typically recommended for rammed earth construction in dry climates, while a 1:1 mix may be more suitable for areas with high rainfall.