Sanding Mill Marks In Wood Trim

By Robert Robillard on Workshop tips

If you want an “A” paint job on crown moldings and trim then you need to take the steps to prepare the wood prior to painting.

This means sanding out the mill marks left on the wood from the moulding and planner blades.

What are Mill Marks?

When boards are run through a planer, the rotating planer knives take shallow bites out of the wood. Mill marks appear as a series of repeating raised bumps that run across the grain of the board.

Look closely at the molding picture below. I drew pencil marks over some of the mill marks and if you enlarge the photo you will see the marks continue down the molding board.

If the knives are very dull, the marks really stand out, but more often they are less pronounced, in some cases invisible to the naked eye but will often show up when light hits the wood at an angle, similar to a sunset or sunrise.

It’s important to note that mill marks are present on every board that has been run through a planer, regardless of quality or source. Sometimes mill marks are very hard to see. If you don’t detect and remove them, they will really stand out once a stain or finish has been applied.

The best way to sight mill marks or any other minor flaws or defects is to use reflected light. Position a lamp above the work surface at about a 30 degree angle to the surface.

You will be surprised when the marks you could not see before now look like mountain peaks and valleys.

The best way to remove mill marks and other minor defects like small surface scratches is by sanding.

This molding will be installed Monday ~ YES! my shoulder is feeling better and I’m going back to work as a carpenter this coming Monday!!!

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About the author

Robert Robillard

Robert Robillard

Carpenter / Remodeler / Editor

Rob Robillard is “The Concord Carpenter” Rob is a builder, general contractor, carpenter, woodworker, and editor of Concord Carpenter and ToolBoxBuzzr As a General Contractor and carpenter, Rob owns and operates Concord Carpenter LLC. A full-service remodeling and construction company. Rob is a recognized leader in home building best practices and a source for how-to information for building professionals. On this website, Rob covers all aspects of home construction, building science, home improvement, woodworking, remodeling, and some of the best product and tool reviews. Rob is in charge of our Tool and Product Review series - Concord Carpenter Videos where we post all of our tool reviews and video tutorials. Rob approaches remodeling and building construction with a pragmatic and problem-solving approach. He enjoys using his knowledge and experience to help and educate building professionals as well as DIYers on best practices in the construction and remodeling industry. He's a strong advocate for "raising-the-bar" in the construction trades and promoting the trades to youth. #BeAMentor #Green2Great Craftsmanship, quality, and pride guide his journey on this channel The Concord Carpenter's motto: "Well done is better than well said!" : Read more about Rob

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