A commercial silicon emulsion was applied to decrease boron leaching from either Na-borate or disodium octoborate tetrahydrate (DOT) treated wood. Treated wood specimens at target retention levels of 4, 8 and 12 kg/m(3) Na-borate were soaked in the silicon emulsion and dried at 105 degrees C for 24 h. In the second trials, wood specimens previously treated with DOT solutions at 1% and 1.5 % concentrations were surface treated with the silicon emulsion. The specimens were then subjected to a 10-day leaching process followed by decay and termite resistance tests under laboratory conditions. Retention levels of 1 kg/m(3) were retained in the Na-borate and silicon emulsion-treated wood specimens after the leaching process, but nearly no boron remained in the wood specimens treated with Na-borate only. In the DOT treatments, about 2 kg/m(3) retention levels were retained in the specimens after the leaching process. The Na-borate + silicon emulsion-treated and-leached specimens showed better performance than the Na-borate only treated specimens in decay resistance tests. The DOT and silicon emulsion-treated specimens remained almost intact even after the leaching process due to higher boron content compared to the Na-borate treatments. Even though termite resistance tests caused higher mass losses in the leached specimens in all treatment groups when compared to the decay resistance tests, silicon treatments also reduced the mass losses in the specimens after the leaching process. More detailed studies are needed to obtain a better understanding of the mechanisms of interaction between silicon emulsion and wood components. (c) 2007 Elsevier Ltd. All rights reserved.