Experimental Preservative Treatment of Three Tropical Hardwoods By Double-Diffusion Processes

The double-diffusion preservative treatment was applied to three tropical hardwoods, cativo (Prioria copaifera Gris.) gallinazo (Schizolobium parahybum (Veil.) Blake), and lechose (Brosimum utile (HBK) Oken), especially common in Costa Rican lowlands, but also common through much of Central and South America. Evaluation was on the basis of the extent of penetration and retention of preservative chemicals. Variables studied included moisture content at time of treatment, effect of incising, soaking time, concentration, and temperature of the treating solution. Duration of soak had the most pronounced effect on retention, but the time needed was shown to depend on the sample condition and preparation, solution concentration, and retention level desired. It was shown that heating of the first solution can reduce the time needed for soaking or it may be employed to increase the chemical retention for a given treatment time. Seasoning and incising effects varied with a given species and also chemical components. With all three species, nearly all the variously modified treatments produced chemical retentions considered adequate to protect wood against severe decay and insect attack. It seems very probable that, with some additional experimentation, schedules for a double-diffusion process could be found that would yield effective treatments of numerous other tropical species.

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