Spalted wood is highly prised for its unusual patterns and colorations, but it's not necessarily easy to work. "Spalting" occurs in an early stage of the decay process, when various colonies of fungi stake their claims to a piece of fallen wood. The characteristic blue-black lines that run through spalted wood actually represent the lines of demarcation between incompatible colonies of micro-organisms and, while beautiful to look at, they mean that the wood is in an early to mid-stage of decomposition. Below, Ellis Walentine and Michael Dresdner offer some expert advice on dealing with spalted wood that's gone a little soft.
Michael Dresdner: "Assuming the spots aren't too mushy, you can pot them with a wood hardener designed to soak in and stabilize rotted wood. They come in two versions — a one package pour on and a two part thin epoxy with names like "Woodrot" and the like. In my opinion, the epoxy is the better of the two. You can get some from System Three here in Seattle — they have ads in most of the woodworking magazines. Once stabilized, you can treat it as any other wood. The epoxy will affect the way it takes stains, but most folks don't stain spalted wood. It will not affect finish adhesion, and rarely affects glue adhesion.
Ellis Walentine: "The mushy spots of any spalted wood are the areas where the spalting has proceeded too far. The best treatment in some cases may be to scrap the wood. If you can't afford (or bring yourself) to do that, there's a type of epoxy that is very thin and foul-smelling designed to harden up these soft fibers (See Michael's answer above).
Otherwise, in situations where the mushiness is not a major functional issue, you can just proceed with sanding and finishing, and use it without trying to harden up those fibers. Avoid pure oil and Danish oil finishes, because they will penetrate deeply into the soft spots and darken them considerably. A coat of wax is the least apt to discolor the soft spots, but if you simply must build a film finish, give the wood a couple thin coats of blond shellac to seal the fibers."
From the Woodworker's Journal eZine 2000 archives.