Commercial antisapstain chemicals in New Zealand

IRG/WP 3142

J A Butcher

Almost all sawn timber of exotic softwoods (principally Pinus radiata) and a large proportion of indigenous sawn timber receives an antisapstain chemical treatment to prevent fungal degrade during subsequent seasoning, storage, or transportation (if exported). Antisapstain chemicals are also widely used to protect freshly peeled round produce during drying. A further, specialised, use is as the fungicidal additive to concentrated boron salt solutions used in boron diffusion treatment of sawn timber; such timber is very prone to mould and stain during the diffusion period. In all cases, the chemical is applied to green timber by momentary immersion in the solution, or by spray. The amount of solution that remains on the surface of dipped timber is very small; solution uptake by dipping green 100 x 50 mm² rough-sawn timber is approximately 18 litres/m³ - equivalent to 1 gal/100 bd ft of 4 x 2 in². The concentration of chemical in solution is that shown by experimentation or experience to be necessary to inhibit almost all fungal growths for a period of 3-4 months. However, adjustment to solution concentrations is often necessary if full cost-effectiveness of the treatment is to be achieved. For example, in winter and early spring chance of fungal infection is usually low, so solution concentrations can be reduced. In contrast, wet warm summers tend to promote fungal degrade and so solution concentrations need to be increased. The condition of the timber also dictates concentrations. Rough-sawn timber absorbs more solution than planer-gauged material, so concentrations must be increased if gauged timber is to obtain adequate protection. This is of particular concern when mills attempt to gauge timber before boron treatment; lack of mould and stain control has limited this worthwhile development. Since antisapstain treatment results only in a superficial deposit of fungicide on the surface of green timber it is merely a preventive, or prophylactic, treatment. The full success of an antisapstain chemical in preventing fungal degrade therefore depends on the timber being free of infection at time of application. Prompt handling between felling, conversion, and antisapstain treatment is a prerequisite of treatment.


Conference: 80-05-05/09 Raleigh, North Carolina, USA

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