Slip straw, or light straw clay, is the third natural building method we incorporated into our house. Comprised of loose straw tossed with clay slip, this mixture is stuffed into removable forms to build a wall that is generally well-insulating. All of the upper floor walls of our house will be slip straw, as well as this small section of wall that faces west in our future living room. Before beginning with slip straw, we built the urbanite stem wall up to the right height and framed the wall with wooden boards.
A table for mixing the slip straw was made from straw bales and a piece of use plywood covered with a tarp.
We then filled a five-gallon bucket with some of the thin clay slip we had perviously made.
Each batch of slip straw was made with one flake from a rice straw bale which we broke apart, fluffing it up and removing all the clumps that were stuck together. We then poured roughly a one-gallon bucket of thin clay slip over it, like salad dressing.
Ryan McCutchan and Michael G. Smith.
We tossed the straw and clay slip like we were tossing a salad. The goal was to get each piece of straw lightly coated in the clay slip.
For forms we used pieces of plywood screwed to the boards that frame the walls. The slip straw was packed into these.
After filling this first one we added another board on top and filled that one before removing the first layer of boards. We proceeded this way removing the bottom board after the top one was full and moving it up.
With every board being removed you kind of wonder if all that straw is just going to fall out, but it doesn't.
The key to getting the slip straw to form a solid wall like this is to tamp it down. The goal is to compact it to the same consistency as a straw bale. Too much tamping could compact it too much and remove the air pockets that make this material a good insulator. We used this simple wooden tamper that Michael made from a piece of scrap wood.
As we moved higher up the walls, straw bales made easy scaffolding.
A crew from the workshop made this quick work. A few people worked mixing the slip straw, someone handed it up to people at the top of the wall, someone else stuffed the slip straw in, and a couple others tamped it down.
Feet make another good tamping tool, as long as it's not overdone.
In a couple short work sessions with a good crew, this wall grew to almost its final height.
Another wall raised... a good reason to smile.