Soak rush leaves for 2 hours in a bucket of water.
Twist the rush leaves into ropes and set them on a wet burlap sheet until you need them.
Take one rush rope and wrap it up around the back side of the seat frame, right next to the upper left-hand corner and leg. Leave 4 inches of free rope at the end and hold it taut.
Wrap the same piece of rush under the left side of the seat frame, right under the upper left-hand corner. Cross the rush under itself and bring it across to the opposite corner of the chair.
Bring the rush under the right side of the seat frame, right under the upper right-hand corner. Cross the rush over the right side of the seat frame, then under the back side of the seat frame, right next to the upper right-hand corner.
Cross the rush over the back side of the seat frame, then cross it under itself and bring it across to the lower right-hand corner. Using the same methods as the other two corners, cross the rush under the front right-hand side, then over, then under the lower right-hand side, then over, then under itself and across to the bottom left-hand corner.
Cross the rush under the lower left-hand side, then over, then under the front side, then over, then under itself and across to the top right-hand corner, where you started.
Continue weaving the rush in the pattern described in the above steps. The rush will get closer and closer to the center, forming an angular pattern. If you run out of rush, attach another piece of rush to the end, using a square knot. Make the knot at the bottom of the chair, where it won't be seen. When you reach the center of the chair, let the rush dry out.
Trim the dried free ends of rush and tuck them into an inconspicuous part of the chair.