For irregular patching jobs, like this one in an exterior privacy wall, plastic window screen and grout can be a cheap, quick, and easy way to do them.
This wall is made of nylon fishnet and cement. Although only about 1/8 inch thick in many places, it has somehow managed to survive hurricanes. You can probably credit that to its irregular shape, which includes a serpentine foundation line. It is the nature of cement to shrink and crack, though. When a banana plant and heavy raceme of bananas fell on it, the wall failed and a big chunk broke out of it.
The patch, made of plastic window screen and grout is probably only about 1/16 inch thick. We shall see how it holds up, but I am confident it will be around doing its job for many years to come.
Step 1: The Hole
This is the hole. I strung a few ropes through it, as best I could, to act as clotheslines to pin the screen material to.
I used my trusty pressure sprayer to clean the area so that the grout would stick well. Grout doesn't shrink, like cement does, so the crack problem should be reduced, or eliminated.
I used a pressure sprayer to clean the wall before applying the grout.
Step 2: The Screen
Here the screen has been put in place using clothespins. The screen comes in rolls. I hung the two pieces I needed vertically so that the seam where the screens overlapped would be vertical and tend to stay together as I brushed on the grout.
Step 3: Adhering the Screen to the Wall
Adhering the screen to the wall was simple. I just mixed up some grout and brushed it on. It penetrated the screen and stuck it down to the wall underneath. (The pink color was just from pigments added for a previous sculpture project.) Painting the seam stuck the two pieces of screen together. Folding it over the top rope made a nice edge.