Hairline Cracks
Step 1
Evaluate the size and location of the crack to the shelf. If it is overly long or a danger structurally, you may have to consider replacing the shelf completely.
Step 2
Fill small hairline cracks with wood fill putty. Use a small putty knife and spread wood fill into the crack perpendicularly to the crack. This will force the filler into the crack better than drawing the knife along the same direction as the crack.
Step 3
Wipe the knife clean and use it to scrape off the excess putty on the wood. Be careful not to pull the putty from the crack. It may take two coats of the putty to get it filled evenly.
Step 4
Sand the crack after it has dried for the duration indicated on the wood fill package. Use fine grit sandpaper with smooth even strokes, following the grain of the wood if possible. When smooth, wipe the wood clean and finish with stain or paint to complete the repair.
Larger Cracks
Step 1
Clean the crack to make sure there is no trapped debris. Use a can of compressed air to blow dust or small flakes of wood from the crack.
Step 2
Use a utility knife to carefully cut out the edge of the crack to create a V shape. This may not be possible for the entire length of the crack, but it will benefit the larger areas.
Step 3
Fill the tip of a putty knife with wood filler and begin slowly packing it into the crack. If the crack is very narrow, the tip of the utility knife may work better. Pack the filler tightly and overfill the crack rather than leave it flush with the wood.
Step 4
Allow the wood fill to dry for the duration indicated in the instructions. Use a fine grit sandpaper to smooth the repaired crack flush with the rest of the wood. Use smooth, even strokes and avoid gouging the repaired wood fill.
Step 5
Clean the shelf with a damp cloth to remove any dust from the sanding. Use wood stain or paint to hide the repair.