Is There a Difference Between Natural and Commercial Mortar for Cordwood?

Natural Mortar Advantages

Natural mortar, typically made from a mixture of clay, sand, and straw or other natural fibers, offers excellent insulation properties, with R-values ranging from R-10 to R-20, compared to commercial mortar, which typically ranges from R-2 to R-5. This is due to the natural fibers, which trap air and create a more consistent thermal mass. In addition, natural mortar is more durable and can last for centuries, whereas commercial mortar has a lifespan of around 20-30 years.

Choosing the Right Mortar Mix

When selecting a natural mortar mix, it’s essential to use a combination of clay, sand, and natural fibers. A typical mix ratio is 1 part clay to 2 parts sand, with 10-20% natural fibers added. The mixture should be tamped into the cordwood cells using a mallet or tamping tool to ensure a tight bond. It’s also crucial to use a natural cement, such as lime, which will help to create a strong and durable bond between the cordwood and mortar.

Mortar Application Techniques

When applying natural mortar to cordwood, it’s essential to work in small sections and use a level to ensure the mortar is evenly distributed. A 1/4-inch layer of mortar is recommended to allow for easy tamping and to prevent the mortar from seeping into the cordwood cells. Use a damp sponge or brush to spread the mortar and avoid creating air pockets or voids. The mortar should be allowed to dry completely before the next layer is applied, which can take anywhere from 24 to 48 hours, depending on the climate and humidity.