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Filling voids in Burls

A burl (or burr) is a tree growth in which the grain has grown in a deformed manner and may contain small voids or cavities. A burl will occur as a round growth on the trunk of a tree above ground. Underground burls can be like a large onion starting at ground level and expanding outward underground, or as a bulging growth among the roots of a tree.

When turning burls, it is important to use sharp tools with light cuts to avoid chipping the burl as a result of the voids in the wood.  

Burls often have interesting and unusual patterns in the wood and can be incredibly beautiful. However, it is quite common to find cracks, pits cavities and voids in the burl, which can make it a little more challenging to work with. Some burls have a combination of these beautiful "flaws", all of which provide an opportunity to create a unique blank by enhancing and emphasizing these features.

                   

 These natural voids can be filled with a variety of materials such as wood sanding dust, metal powder or crushed stone powder if the voids are large.
  • Metal powder is commonly used for filling voids as its shine provides a natural metal accent to highlight the interesting void pattern. Copper powder, brass powder and aluminium powder are the most common.
  • Stone powder, made from crushing semi-precious stones, also provide a natural and beautiful way to fill these voids, often with bright colours.
  • Other substances such as coffee, baking soda or paint powder may also be used and depending on the colour of your wood burl, these may create the desired effect. In fact practically any fine powder substance may be used to fill these voids and you may be able to find many some not mentioned here that produce a super finish.

Fill the voids following these simple steps:

  1. First turn your burl down to the desired size or slightly larger leaving room to sand the piece down.
  2. Identify the voids that you wish to fill and take note how deep they are. Deeper or larger voids may require multiple "coats" of fill to achieve a solid and even fill.
  3. Pack the void with the powder of your choice and saturate with CA glue.
  4. Fill the void to a level above the surface of the wood so that you can sand the filled area level to the turned piece.
  5. The same effect can also be achieved by mixing your powder with clear epoxy. The longer drying time and the ability to mix the powder in with the epoxy may be preferable for filling larger voids.
  6. Once the piece is filled, allow it to dry completly before sanding and finishing it.

The diagram below shows burl voids filled with copper powder.