Slip straw is a great beginning natural building technique because it is quick to learn, simple, and can be used in new buildings or to add non-toxic insulation to existing buildings. Ben Waldman, contractor and natural builder, taught a slip straw workshop at the GrowHaus in Denver last month.
Workshop participants included permaculture students, landscapers, farmers, and people who wanted to explore options for building projects they have coming up.
Slip straw is made by combining fiber (preferably wheat straw) with a runny clay slip. The hollow shaft of the straw creates air pockets, while the clay binds the fiber together and adds thermal properties.
Once the straw and clay slip have been mixed to the right consistency, the mixture is added into a wall’s framing and then tamped down.
Slip straw is not load bearing on its own, but is meant to be used as an infill for framed walls. Different framing designs were discussed, along with their advantages and disadvantages for combination with this technique.
Once the straw has been fully tamped into the wall, it will be finished with a clay or lime plaster. Clay is able to control moisture on its own, which helps protect infill of the wall against mold or rot.
Clay plaster is another huge topic that will be taught at a future workshop, but students in this class got to have some hands-on introduction.
Burlap coated in clay slip was added over wood framing members to help bind the plaster to the wall.
Students left the workshop having gained firsthand experience with natural materials, knowledge of how to achieve the right mixtures for slip-straw and the steps involved in applying this method for better wall insulation, and access to additional resources.