When they give you those big puppy eyes, you have no choice but to forgive your dog for chewing up your windowsill. Then the culprit will wander off to take another nap, and you'll be the one in charge of windowsill repair. The process is a lot like repairing scratches in a wooden door, which is another DIY project that many dog owners have to take on at some point. It's a good thing that pup is so cute!
Wood Filler or Wood Putty?
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The chew marks created by your dog have to be filled in with something. There are several products that can be used for windowsill repair. The severity of the damage from a dog chewing on windowsills may determine what kind of material you use for the fix (or whether you're better off replacing the windowsill altogether).
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Wood filler is a combination of wood fibers and resin material. Once it cures, wood filler is extremely hard and can be sanded and stained. (If you have access to sawdust, you can experiment with making your own wood filler by mixing sawdust with glue or lacquer.) It's probably what you'll want to use if there are chunks missing from the windowsill. Wood filler cures to be so hard that it shouldn't be used for outdoor repairs since exterior wood shrinks and contracts depending on weather conditions.
There are also many wood epoxy and wood putty products on the market. These are thicker solvent-based products. Wood putty remains a little rubbery even when it hardens completely and usually shouldn't be sanded or painted, so it's best used for filling in small holes or chew marks that don't need to be sanded. When in doubt about what product to use, opt for wood filler.
Things You'll Need
Utility knife or screwdriver
Orbital sander or sandpaper
Cloth
Wood markers or paint
How to Repair a Chewed Windowsill
Step 1: Prepare the Sill
Chip away any loose wood chunks or slivers from the chewed area with a utility knife or screwdriver. Get down to eye level to check whether any chewed wood is sticking up above the surface of the sill. If it is, sand down the area with an orbital sander or a piece of fine-grit sandpaper. For minor damage, you may decide to skip sanding at this point; you're going to sand the surface smooth after it's patched.
Step 2: Apply Filler
After reading the package directions for your wood filler, use a putty knife to pack the chewed areas with the resin. Add enough filler to build up the sill to its original dimensions. Smooth out the filler using the putty knife but don't worry about getting it perfectly smooth. It's better to overfill the gouged areas than to underfill them. You can remove excess wood filler once it hardens, but adding too little filler will leave depressed areas in the wood.
Step 3: Sand the Sill
Let the wood filler dry completely according to manufacturer directions. How long this takes depends on the depth of the gouges you filled in, but it shouldn't take more than a few hours tops. Sand the sill until the patched section is flush with the surrounding wood. Use a damp cloth to wipe away any dust.
Step 4: Paint or Stain the Sill
Paint or stain the sill to blend the repaired section with the original wood. You may need to repaint the windowsill trim too. If your sills are made from unpainted wood, use wood markers to carefully draw faux wood grain onto the patched spots to match the surrounding area.