In this study, two colloidal dispersions of pure amorphous silicon dioxide particles, acetylated, and heat-treated samples were tested for a possible application as a wood protection agents. The silicon, acetylated, and heat-treated samples were exposed to an accelerated weathering experiment, and their dimensional stability was assessed. The weathering experiment comprised cycles of 2 h UV-light irradiation followed by water spray for 18 min. The surface changes of the weathered samples were characterized by FT-IR spectroscopy and color measurements. According to results, the silicon treatments showed lower color changes than untreated ones. However, acetylated and heat-treated samples provided the lowest color changes. The resistance of the silicon, acetylated, and heat-treated wood to decay was studied by means of brown and white rot fungi in laboratory decay tests. Decay test results revealed that acetylated and heat-treated wood samples showed better decay resistance against P. placenta and C. versicolor than silicon treatments. Samples modified with silicon were exposed in above ground standard lap-joint test in Ultuna, Sweden. The dispersions of pure amorphous silicon dioxide impregnated in wood did not significantly influence its hygroscopic and dimensional behavior. However, the silicon treatment reduced the color changes caused by weathering. The silicon impregnated samples showed a weak fungal discoloration similar to that of chromated copper arsenate impregnated controls in above ground standard lap-joint test. (c) 2006 Wiley Periodicals, Inc.