Wood products, especially those used in outdoor conditions, can be damaged by dimensional changes and decay fungi. It is therefore advised to use impregnation treatments to mitigate these hazards. While the potency of the chemicals employed in the treatments is important, characterization of the treatments is also crucial to ensure deep and durable protection. In this study, eastern white pine (Pinus strobus L.) and white spruce (Picea glauca (Moench) Voss) were impregnated with propiconazole and 3-iodo-2-propynyl butylcarbamate (IPBC) through diffusion. Instead of using pressure treatments, the samples were dipped in solutions containing amine oxides, which can diffuse into the wood. The treatments were characterized by the mass of fungicide impregnated, fungicide leaching, and the impregnation depths of both the fungicides and the amine oxides. It was found that the treatment impregnated slightly more than 0.040 kg/m3 of both fungicides, meeting EU standards. It was also shown that the presence of amine oxides slightly prevented the leaching of the fungicides in white pine. The penetration of the amine oxides was several millimeters deep in all directions, but the penetrations of the fungicides were much shorter and only longitudinal.