Putting the "log" back in Blog

Get Woodworking Week: Filling Knot Holes

Posted on February 8th, by Andy Brownell in Around the shop, Gorilla Glue. No Comments


This is a post I originally made back in 2009 following Woodworking in America. Here’s an easy way to fix some mistakes (for beginners or advanced woodworkers) with Gorilla’s 2-Part Epoxy. I’ve also got a video posted here on Tube in case you don’t feel like reading.

The wood that I obtained from a local source was decent, but certainly not top grade material. It had some knots on otherwise clear boards, and it just didn’t seem right to trash a huge piece on account of a few minor imperfections. The inside of the bookcase only had one spot the size of a dime that needed repairs. The remaining boards were the undersides of shelves, which again, will rarely, if ever be seen once in place. So while aesthetics were not a primary concern for this cosmetic repair of otherwise nice boards, I did want to fill the knot holes with something that was stable, but had a little give to allow for movement over time. Enter Gorilla Glue’s new epoxy.

When I was learning the basics of furniture construction at J. Miller Handcrafted Furniture, Jeff showed me this great technique he used to simulate inlay, without all of the fuss of wood movement. He used a slow setting epoxy mixed with a black dye to create the look of fine grained ebony inlay. Knowing this worked for his projects, I figured I’d give it a try with some of the knots in my bookcase.

Ingredients and Preparation

The two part epoxy comes as a clear formula, so I needed to simulate the color of the native wood (perhaps a little darker), to still keep the appearance of a naturally occuring knot in the wood’s surface. I used my random orbit sander with my built in dust collection bag to capture the fine sanded grains of wood from the same surface I was filling. For a hole of this size, I only needed about a teaspoon worth of the fine sawdust. I mixed a bunch more, because it is better to have too much, than to run out mid-stream.

Next I add in about 3x the volume of epoxy to sawdust in a disposable mixing cup, and gently stir the mixture until all of the ingredients are well blended. Try to avoid mixing to vigorously so you can keep out the bubbles. At this stage, the epoxy mixture will begin to resemble the darker color of your wood surface (if wet), and will be about the same consistency as a thick cake batter.

Then, on a taped- off surface (blue painters tape is best) around the area to be filled, either gently pour, or spoon in the epoxy mixture to the hole needing to be filled. Simply spread the mixture around until the hole is filled in completely. Don’t worry about a mess, that’s what the painters tape is for. Be sure to leave a generous amount over the hole, extending beyond the level of the board. This allows for any settling that may take place, and the remaining amount is removed once cured.

The Waiting Game

Allow for the full 24-hour recommended cure time before peeling away the tape. Most of it should lift off with a little effort, just be sure not to get too close to theedge of the area that is filled in. Then using a small, sharp and finely tuned block plane, i shave away the pieces of epoxy right to the surface of the wood. Take small shavings – resembling something akin to large skin flakes from a bad sunburn – to avoid tear-out of the epoxy. I then sand the surface with 220 grit sandpaper.

Results and Verdict: The final surface will receive my favorite finish, Watco Danish Oil (wet sanded) and butchers wax. I have applied some water to the surface for now to simulate what it will look like finished. Overall, I am fairly pleased with the results, and will certaily use this technique in the future if I have any minor imperfections to fill, or for wood that will be painted. For larger repairs that need the natural wood appearance, and are more visible, this may not be the best approach, however as I said most of this will be invisible to human eyes for the next 100+ years, and I can live with that.

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