SPALTED WOOD
What causes spalting?
Wood infected by fungi which during natural process of decay have created a pattern of light and dark areas usually bordered by black or brown lines. Lines called zone lines
Spores, via the air or ground, contact the wood and germinate producing a strand of mycelium (vegetative part of the fungus, tube or threadlike). The mycelium branches and rebranches to form an interwoven mat. At the tip of each mycelium are digestive enzymes that absorb and metabolize the wood cell structures.
As fungus advances it leaves nutrient-poor areas behind. The degree to which the fungus decays the wood depends more on the type of fungus than on time.
Appearance of mushrooms, conks, etc is indication of fungal activity in the wood.
Three types of fungus rot: soft, brown, white.
Soft rot fungi advance slowly and cause less structural damage than do brown and white types. Example: “blue stain in pine” Also color streaks in ambrosia maple. Fungus introduced by the ambrosia beetle.
Soft and brown rot fungi metabolize only the cellulose, while the white rot metabolizes both cellulose and lignin.
Cellulose: long chain polymers, orientation of the molecules with the long axis of the wood cells account for many of the basic properties of wood.
Lignin: about 25% of wood composition, complex and not understood; acts a binder for the cellulose fibers
Thus when lignin is attacked the structure of the wood is undermined. Pigments that color the wood are mainly in the lignin, so advanced stage of white rot leaves the wood looking bleached and is soft and fibrous. But the white rot fungi are chiefly responsible for the zone lines.
Zone lines result when 2 different fungus colonies meet.
How does one create spalted wood?
Necessary conditions:
1) Food: normally present in the wood
2) Temeperature: 74 to 90 F
3) Moisture: above 26% and less than 40% (above 40% -- not enough oxygen; below 26%, growth won’t continue) Drying below 20% prevents fungus growth
4) Oxygen: wood must have at least 20% air. As moisture increases, air content decreases
Lumber industry will store logs in ponds to prevent attack from fungi
Sow what does the woodturner do to get spalted wood?
Need fresh cut wood. Cover it with wet leaves and keep out of the sun. Easy to do on the coast or back East. Other approaches : put piece of spalted wood on the freshly cut wood. Put the fungus on the wood. Takes 1 to 2 years. In our climate, best to bag up the fresh wood.
Which woods will spalt?
“heartwood” resistance:
Slightly resistant: Ash, Beech, Birch, Cottonwood, Elm, Maples, Poplar, Pines, Sycamore
Moderately resistant: Douglas Fir, Larch, Tamarck
Resistant: Cedar, Black Cherry, Chestnut, Juniper, Mesquite, Bur Oak, White Oak, Osage-Orange, Redwood, Black Walnut, Yew
How to turn and treat spalted wood:
From Mark Lindquist:
Rough turn on lathe, then final shape via body grinders and disc sanders. Dry in microwave oven. Finish sand using foam backed paper. Finish with mixture of linseed oil and high gloss polyurethane varnish. Buff with tripoli
From Robert Lentz:
Uses face plate with 12 or more screws, 1.5 to 2.5 inches long. Dries small items in microwave; larger ones – air dry. Uses CA glue for repairs. Finishes with mineral oil followed by Deft semigloss clear finish, buff with steel wool. Final buff with cotton pads – minerla oil ; rub with tripoli.
From Ron Fleming:
Use 50-50 mixture of dish soap and water (Ron Kent does this) to reduce tear out. Apply with paper towel while rotating. For drying – coats inside and outside with soap solution. Covers with plastic bag- uses clothes pins at lip. Once a day turns bag inside out. Takes up to 2 months. Finishing – waterlox on inside and a layered lacquer finish on the outside.
Johnson:
After roughing out and drying. Apply CA, epoxy, or Minwax woodhardener.
Lots of sanding. Finish with poly-finish.
Gerton:
Loads of CA
Health concerns with spalted wood:
Older literature warned of many things about the fungi. More recent research done at BYU does not indicate that there are toxic are carcinogenic issues. Airborne spores may induce allergic reactions similar to dust from many woods. Some people are allergic to molds, etc and should take appropriate steps. In general, use dust collectors and masks, and even air-filtering hoods.