The combined effect of boric acid impregnation together with boron steaming and steaming heat treatments were evaluated in this study. Boric acid pre-treated wood samples and untreated ones subjected to steaming heat and direct steaming treatment in a close reactor at 13 bar pressure and 180 ºC for 30 minutes. Compression strength parallel to grain of wood samples, leaching test and pH measurements were performed. Quantity of boron in leached and unleached wood samples was determined with ICP (Inductively Coupled Plasma). Retention values obtained in treatments were enough to protect wood against many wood degradation organisms. Approximately 32 kg/m3 and 2.52 to 14.1 kg/m3 retention was obtained in pre-treated samples with vacuum impregnation and treatments in boron steaming medium respectively. After the treatments, all of the samples got dark color and became more brittle due to thermal degradation of wood components. A significant decrease on the compression strength parallel to grain of wood samples was monitored especially subjected to direct steaming boron treatment. Depending on pre-treatment and applied second treatment, strength values were decreased with a range of 6 to 27% compared with controls. Since strong acidic conditions tend to catalyze hydrolysis, dehydration and oxidation reactions in wood that adversely effect the strength of wood, treatments at high temperature caused strength losses. Heat treatment had less degradation potential than steaming in the study. Treatments in boron steaming medium have no/little effect on boron release and almost all boron was leached from the wood samples. Only boron steamed samples decreased boron leaching with a 20% rate. Biological resistance tests are needed to evaluate the performance of the treatments in both leached and unleached samples.

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