Measure the inside opening of the sliding screen door in both directions. Add 2 inches to each measurement. Cut a piece of thin cotton fabric matching this new measurement.
Remove the screen door from the tracks and lay it on the lawn with the spline side up. This is the side that shows black, licoricelike strands pushed into the channel around the screen’s edges.
Pull out all four spline pieces from around the screen. Use the tip of the spline tool to dig underneath one end of each spline and grab the end. Pull the spline up and out. Discard the old spline. Remove the screening and roll it up, setting it aside in case you want to replace it later.
Lay the fabric on top of the door opening. Move the fabric around until there is a 1-inch overhang on each side of the opening. Secure the fabric in place with small pieces of masking tape.
Measure the spline channel length at the top of the opening and cut a new spline piece matching this length. Lay the spline on top of the fabric over the channel. Push the spline into the channel using the spline tool. The spline encases the fabric’s top edge between the screen frame and spline material.
Cut the spline and insert it into the bottom channel, pulling the fabric taut. Do the same with the two side channels. Pull and manipulate the fabric until it's straight and taut in all directions.
Trim any fabric edges showing outside of the splines by cutting the cloth right up to the spline. Leave about one-eighth-inch overhang.