Light Clay Infill
There are two main types of light clay infill.
1. Slip N’ Chip
This is what we tend to call light clay woodchip infill. For areas where there are mills, this is a particularly convenient and appropriate building technique to use. Clay and water are whipped into a runny milkshake consistency (called clay slip) and then “tossed” together with the woodchips, ensuring that the woodchips are thoroughly coated, but not sopping, with clay.
This mix is then tamped (a firm, yet gentle pressure is used) into the cavity of the walls.
To achieve the cavity a balloon frame is built in the carpentry/framing stage of building, and forms are affixed to the exteriors of the framing. The cavity is usually made to be from 6” to 1’ thick. The forms are much like concrete forms, with plywood covering one side of the wall completely, and 2’ thick strips of plywood being leapfrogged on the other side. The leapfrog side is where the workers have access to the inside cavity.
The forms may be taken off immediately to allow the walls to dry.
To ensure the infill is locked into the walls well keyways are often placed inside the framing.
2. Light Clay Straw
This mix consists of loose straw being tossed with clay slip. The process is the same as for slip n’ chip.
The main performance difference between the two comes down to thermal performance. Since the straw naturally has trapped air within itself, a light clay straw wall tends to provide better insulation.
Availability of the raw materials is something to consider. Being located on Vancouver Island, where we have a large wood industry and virtually no straw providing industry, the woodchips become an obvious choice when wanting to keep costs down and materials more local.
Alternatively, a reed matt (or something similar) may be used as a permanent form. This eliminates the need to use plywood (even if it is a temporary use) and keyways. It also gives a nice even and clean surface for plastering onto later.