Lumber Stains and Their Control in Northern White Pine

Northern white pine (Pinus strobus L.) logs and lumber frequently develop stains which reduce their value. Losses from staining have increased with increased summer logging and from increased proportions of sapwood in smaller diameter logs. Many stains are caused by fungi. Among these the most common is blue stain, a deeply penetrating bluish discoloration caused by fungus of the genus Ophiostoma. A chocolate-brown stain which develops in stored lumber is also caused by fungus. A pink to intense red stain is often an early stage of the red ring rot caused by Fomes pini. Practices which retard drying such as solid piling favor the growth of molds, which may be green, purple, red, or black. Mold stains can usually be removed by planing, though the stains caused by the fungi which are usually also present are too deep to be removed by surfacing. Among chemical stains, coffee stain is the most common. It is thought to be caused by sugars which are concentrated and brought to the surface during drying. Shortening the storage period for logs, and shortening the period of solid piling of freshly sawed lumber to one day are effective preventives for coffee stain. Sap stains caused by fungi can be controlled by logging white pine and sawing it during colder seasons. Another measure is to season the boards rapidly by end-racking or triangular piling. Pine lumber sawed during the warm season should be dipped in a stain-preventive chemical solution and immediately piled to season rapidly. Stain-free logs must be obtained at the sawmill if dipping and rapid drying are to be effective. Treated stock should be protected from rain and promptly placed in well-located seasoning piles. Dipping treatment of 4 by 4 lumber consumes approximately 15 gallons of stain-preventive solution. costing 15-20 cents per 1,000 board feet. Interior stain, caused by delay in chemical dip treatments after sawing or. by deep stains in the log, sometimes appears during resawing or surfacing. If lumber dip treatment is delayed at concentration yards, it is recommended that dip treatments be made at small sawmills before the lumber is moved to the concentration yard. Solid piling of chemically dipped lumber to be kiln dried is safe for several weeks if the treating concentrations for chemicals are doubled.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member