Structural Crack Filling

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Blog entry by Ancientwood posted 08-24-2009 11:35 PM 1422 reads 0 times favorited 4 comments Add to Favorites Watch

Ancientwood has developed a technique for filling large, structural cracks, sometimes found in Ancient Kauri slabs. This is a step-by-step approach for creating a flat surface with beautiful patterns and design.

1. The slab must first be flattened. This can be done with a drum sander, planer or a CNC router.
2. After the slab is flat, locate cracks that need filling.
3. Fill any hairline cracks with color-matched latex putty. Wet the adjacent area of the Ancient Kauri with spirits to get an accurate color match for the putty (be careful not to get mineral spirits on the crack you are filling!)
4. Locate any larger cracks that may continue through to the underside of the slab.
5. Remove any bark within the crack (reserve for future use).
6. Dam the bottom of the crack by clamping wax paper and plywood to the bottom of the slab.
7. We use clear epoxy mixed with finely ground Ancient Kauri bark as the filler.
  • Grind collected bark with coffee grinder or something similar.
  • Sift ground bark with flour sifter to filter out the larger pieces – set aside.
  • Mix your epoxy (we use West System 105 epoxy resin and 207 special coating hardener), being careful not to create too many bubbles and making sure to combine both parts thoroughly.
  • Once the epoxy is mixed, add enough of the ground and sifted bark while slowly stirring to create a consistency similar to peanut butter. For a large crack you may want this thicker, and only partially fill the crack the first go. You can add more epoxy after the initial filling. We often use the epoxy clear on subsequent fills. This allows an opportunity to “see into” the wood, giving an interesting sense of depth to an otherwise flat surface
    8. Use a flat blade tool to push the filler into the cracks until they are slightly over-filled (if not enough is added to fill the crack, a divot will appear after sanding).
    9. Sand up to 2000 grit, carefully sanding the epoxy, as it will be much harder than the surrounding wood.

4 comments so far

View a1Jim's profile


117721 posts in 4084 days

#1 posted 08-24-2009 11:39 PM

Interesting aproach,thanks for sharing.

View Scott Bryan's profile

Scott Bryan

27250 posts in 4329 days

#2 posted 08-25-2009 12:04 AM

That is an interesting technique to fill cracks. It should be applicable to other woods as well.

Out of curiosity rather than using ground bark have you ever tried using sanding dust?

-- Challenges are what make life interesting; overcoming them is what makes life meaningful- Joshua Marine

View RBWoodworker's profile


441 posts in 3858 days

#3 posted 08-25-2009 05:38 PM

It works really good and is a solid fill and usually prevents the cracks from spreading.. however..this type of filling does not take a stain, so while it’s great for natural finishes.. if your going to stain your piece..I wouldn’t recommend it..another thing I use instead of sawdust is chalk from colored crayons.. if my piece is of an odd color..I try and color-match using the chalk crayons of different shades till I get the correct great when mixed with the epoxy..Just rub the crayon on a piece of sandpaper to get the powder and add it slowly to the epoxy..

-- Randall Child

View Ancientwood's profile


10 posts in 3764 days

#4 posted 08-25-2009 06:31 PM

Yes, we have used sanding dust and it works great. In fact, mixing in dust from other species (and products) will result in some interesting color changes.

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