I saw the instructable on making shelves out of Longboards (https://www.instructables.com/id/Hanging-Shelves-Made-From-Longboards/) and wanted something similar but out of a used skim board. It's smaller and the one we had was decorated so I used the back half as artwork, so it's both art and a shelf!
One skim board of your choice
two small and two large L brackets with necessary screws.
Jigsaw and screwdriver
Step 1: Picking the Board
You should pick a board that is good quality but that you are willing to cut and never use as a board again.
Step 2: Cut the Board
Pick a straight line across the board, mark it somehow and cut along it using a Jigsaw.
Note: If you use tape put it on the back of the board, i.e. not on any decals that might be torn off. I learned the hard way! See just above the cut, where the tape peeled it off.
Step 3: Attach the Back to the Shelf
Using L brackets, attach the back of the shelf to the shelf. This creates the stand alone shelf and back. This step is optional because you could just attach the back to the wall somehow. I chose this method to keep things simple and lined up.
For the very detail oriented only; I made sure to keep the shelf half approximately 1/4 inch off the wall to leave room for the back. I also placed the back approximately 1/4 inch high to that it doesn't cover any part of the bottom. That way the bottom exactly matches up with the top.
Step 4: Pick a Place and Attach It to the Wall and Then Done!
Using another set of L brackets, attach the shelf to the wall.
Step 5: Finished Product
Now you've completed the Skim Board shelf project! Congratulations.