How to Use Wood Filler for Projects and Repairs

Repair cracks, dents, holes, and more with these tips for using wood filler.

While learning your way around a saw can improve your woodworking chops, learning to use wood filler properly will give your projects and repairs a professional edge. This common product might seem simple enough to use, but there are many types of wood filler, each with its own intended purpose and best use cases.

Once you learn the varieties of wood filler and how and when to use each one, your surface repairs will be long-lasting and virtually invisible.

Wood filler is a hardening substance used to fill imperfections in wood surfaces. The solution often consists of tiny wood fragments suspended in a water- or petroleum-based binder.

Types of Wood Filler

Below are four of the most common wood filler varieties used by DIYers. Note that there are many specialty wood filler varieties and you should always consult the manufacturer's instructions for each product's specifications.

When Not to Use Wood Filler

Wood filler is intended to fill small voids for visual repairs and should never be used as a substitute for fasteners or other joining materials, such as glue. Larger damage and structural issues cannot be mended by wood filler and an alternative repair will be necessary.

Additionally, rotten, structurally compromised wood will need to be reinforced and repaired, with wood filler being reserved as an optional last step to smooth the top layer. Wood hardener can be applied to soft, splintered wood to help reinforce it before the wood filler is used.

How to Pre-Tint Wood Filler

Many wood fillers come tinted to allow the user to better match the filler to the material. However, these and other fillers are often labeled as "tint-able," which means colorant can be added to the filler before application, allowing for custom color curation. While this can be very handy, it can also be a little tricky to get the color right. Some fillers require a darker stain to match a material, while others do better with a lighter stain. Sometimes, you'll find no stain at all results in the best shade.

Take your time and practice on a scrap piece, letting the filler dry before utilizing your mixture on your finished piece. Keep in mind that water-based fillers must be mixed with water-based stains, while petroleum-based fillers require solvent-based stains.

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How to Use Wood Filler

Follow these steps to learn how to use both water-based and petroleum-based wood fillers. For best results, consult the manufacturer's instructions for your specific product alongside this basic guide.

What You'll Need

• Water- or petroleum-based wood filler

• Stiff putty knife

• Tack cloth

• Vacuum

• 220-grit sanding block or orbital sander

• Rag

• Cleaning solution (reference manufacturer's instructions)

Step 1: Prep Material

Before attempting to fill the material, prep the surface. Sand away any rough edges and remove all dust and debris.

Step 2: Mix Wood Filler

Use a small, stiff putty knife to mix the wood filler in its container until it's thoroughly combined and has a consistent texture and color throughout.

Editor's Tip: If using petroleum-based wood filler, return the cap whenever you aren't actively scooping filler from the container to prevent it from drying out.

Step 3: Fill the Void

Use the putty knife to smear the wood filler into the void, being careful to not scratch the wood surface. Build the filler up above the wood surface to account for shrinking as it dries, but refrain from applying too much wood filler, as this will drastically increase the time you spend sanding. Let the filler dry according to the manufacturer's instructions.

Step 4: Sand the Filler

Once you've ensured the wood filler has completely hardened, sand it until it's flush with the wood surface. Sanding by hand is recommended, but a powered sander is an option if the wood filler is too hard. For more sanding control, opt for a higher grit, like 220. Once you reach the wood's surface, sand in the direction of the wood grain to better match the wood's surface.

Step 5: Finish the Material

Finish your DIY wood project as you normally would. Sanded wood filler tends to leave plenty of dust behind, so remove it with a vacuum followed by a tack cloth before applying your finish.

How to Clean Up Wood Filler

When it comes to cleaning up your tools and other surfaces, check the manufacturer's label for complete instructions, including products for removing the filler. Most water-based wood fillers will easily come off with water, especially if tackled before they have time to harden. For petroleum-based fillers, manufacturers often recommend mineral spirits or other solvents.

Editor's Tip: If you leave the wood filler to harden on your metal putty knife, you can easily remove it by placing the knife against a work surface and sanding away the filler using an orbital sander.