How to spalt wood

Updated: May 6, 2019

spalted-maple-bowl-isolated-on-white Frank Anusewicz/Shutterstock

Wood rot isn’t exactly what you’d consider attractive. But under the right conditions, it can be. The patterning caused by fungus in wood is called spalting. It occurs naturally in dead wood, or you can create it yourself.

Choice woods for spalting are those prone to rotting, such as poplar, maple, and birch. Under ideal conditions, you can make spalted wood in a couple of months, though results will vary depending on fungal and wood species and the climate in your area.

My best results came from using wood with a moisture content of 30 to 50 per cent. Since fungi need a moist environment to grow, wet wood provides an ideal habitat for broad colonization. First, find a patch of damp ground with rich soil. If you’re using a block of wood, place it with the end grain in contact with the earth; for a board, lay it flat. Cover the wood with sheet metal roofing or plywood to help keep in moisture.

Coloured streaks will appear on the surface when fungi take root.  Leave it for at least six weeks, then inspect every two to three weeks for more signs of coloration. Occasionally poke a pocket knife into the wood to test the density—it should have some give, but you don’t want to wait until the wood is spongy.

Satisfied with the colouring? Scrape off the soil, and hose it clean. Put your spalted wood on blocks or a pallet to allow it to dry and to stop the spalting; cover with sheet metal or plywood to protect it from rain. After a couple of days, coat the ends with an exterior paint or varnish to slow evaporation and reduce checking (small cracks from the wood drying too rapidly). Outside, your wood will dry to about 15 per cent moisture. Bring it indoors until it’s 8 to 10 per cent before milling into your finished product; otherwise, it will keep spalting, and your wood will be too soft.

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