A method of treating a wood object against unwanted effects caused by fire or, correspondingly, micro-organisms or insects. The wood object is treated with a mixture which comprises at least one active substance, which active substance or active substances are mixed into a liquid intermediate substance before use. A liquid dispersion of an agent that increases the hydrophobicity of wood, such as an aqueous dispersion of alkyl ketene dimer or alkenyl diketene dimer, is added into this mixture. By treating the wood object with a mixture that is generated in this way, the active substance will remain in the wood, and it is possible to prevent or significantly delay rainwater flushing it out.
