Wall patch requires sanding so that it can be undetectable. The proper tools and techniques are need to properly sand the area in order to produce a flat, even surface. Wet sanding is one of the best techniques for this type of repair.
1 - Using Fine Sandpaper
Use a150 grit fine sandpaper to do your sanding work. Purchase sandpaper sheets that will fit into your hand sander. Install the paper, securing one end of the paper under the hand sander clamp. Pull the paper taut and secure it under the other clamp. Tighten the clamp screws.
2 - Preparing the Area
Go over the entire wall with the hand sander. Mark any raised areas with a pencil. Use the light from a lamp to check for any difficult to see problem areas.
3 - Repairing Gouges and Ridges
Use a trowel to apply a layer of joint compound to areas that have gouges or ridges. Removing dent damage with sanding will require more effort and time. Sanding should be done once the compound is dry.
4 - Light Sanding Techniques
Be careful not to over sand an area or scrub back and forth. Hold the sander on a slight angle. Lightly press the sander on the patch area.
5 - Priming the Area
Prime the area that was repaired. Once the primer has dried, lightly sand the area again. This sanding step is important to creating a surface free from any fuzz or lumps. Apply a second layer of primer to the area. Sand the primed area again, once it has dried.