Brief :

Light Slip Straw Wall or Straw Clay Wall is an infill wall system of loose straw lightly coated in clay that is packed into forms to insulate and enclose a building. In an attempt to implement this system in a project where rice and millet straw is available in abundance, it was decided by the team to try the technique hands-on in a 1:1 panel. The main objective is to understand the construction technique, its material proportions, effectiveness, and most importantly - how does it function in time

Material Procurement :

For the wall frame, one can go with any local wood or bamboo that is available. For this sample we have used Pinewood for our frame. Straw is essentially a farming waste; hence, it is readily available. Choosing the right type of clay for making the slip is necessary for a good bind. As we were only making a sample terracota clay was obtained from a local pottery studio for the works.

On site we intend to take the site mud (it is clay-ey), add lots of water to it in a drum, let it settle and take the top "creamy" part for using as slip

Making the frame:

The depth of the frame can be decided based on the function that the wall shall be serving. For our first panel, we decided to go ahead with a 100 mm thick wall as we wanted to explore whether it will withstand as an external wall. The cavity for the straw filling was 600mm x 1500mm (2 feet x 5 feet). 2 wooden sections were further fixed internally on each side creating a key for the straw mixture.

Making the straw mixture:

To understand the quantity of straw required, a 25 kg cement bag was considered as an approximate measurement. For the preparation of clay slip, the ratio of clay to water we arrived at while slowly slowly addign water was 1:1.5. The slip should look watery enough to create a thin layer when a clean hand is dipped in it and does not drip. Once the slip is prepared, start sprinkling it onto the straw. The straw should be tossed in the slip and not drenched in it. To check the consistency of the prepared straw, take a portion and twist it – if it drips clay or sticks to your hand, the straw is too wet. Add more straw in this situation. And if the straw is unable to retain the twist, it can do with some more slip. The perfect consistency of the straw is when we twist the straw and it retains its shape as is.

Making the wall:

Before we prepared the slip straw, the frame was fixed with planks of wood of 1.5 feet as formwork. After this, a small quantity of the straw mixture was stuffed in the panel and tamped (compressed) down using wooden members. Wooden strips were added into the frame at equal intervals of 2 feet. 2/3^rd wall was completed on the first day of construction. Before starting the remaining construction, the topmost surface of the completed layer was scored and slip was sprinkled onto it to reactivate it. The last third was done on the second day of construction. The formwork was removed after 48 hours of completion of the wall.