Can Cordwood Walls with Natural Mortar Survive Heavy Rain?

Designing for Water Resistance

Cordwood masonry construction involves stacking horizontal logs end-to-end, with the log ends facing outwards. This design allows for efficient use of space and creates a natural water-resistant barrier. However, the joints between the logs still require a high-quality natural mortar mix to ensure water tightness. A ratio of 1:3 cement to sand is a good starting point, with the addition of natural fibers like hemp or flax for improved tensile strength.

Building a Rain-Resistant Cordwood Wall

To build a rain-resistant cordwood wall, start by excavating a trench for the foundation, sloping it to allow water to drain. Then, lay a layer of compacted gravel, followed by a 2-inch layer of natural mortar. Begin stacking the log ends, overlapping them by 2 inches to create a staggered pattern. Apply a thin layer of mortar between each log, making sure to fill the gaps tightly. As you build, use a level to ensure the wall remains plumb and the mortar sets properly.

Additional Considerations for Heavy Rain

Insulation is crucial in cordwood construction to prevent moisture buildup. Use a minimum of 2 inches of insulation, such as cellulose or wool, between the log ends and the exterior of the wall. Additionally, consider applying a waterproof coating to the exterior of the wall, such as a natural oil-based sealant or a lime-based render. This will help protect the cordwood from prolonged exposure to rain and maintain its structural integrity.