In order to prolong the usage of wood one needs to prevent the growth of rot and fungi. The most common substances used today are not environmentally friendly and they need to be replaced by more environmentally friendly options. Water glass or sodium silicate has been known for a long time having properties which give the wood resistance to rot and fungi and in addition also fire retardant properties. The present invention discloses a method for treatment of wood to improve the flame retardant properties and also the resistance to rot, fungus, mold and insects of a wooden material. The wood treatment method of the invention comprises the steps of providing a wooden material and providing water based formulation which is stable in room temperature or in temperatures ranging from 15-35° C. The water based formulation of the invention consist essentially of an alkali metal silicate, water and an insolubilization agent which is selected from an organic acid, an inorganic acid or an inorganic polyvalent ion, added in an amount lower than the amount of insolubilization agent needed for the formulation to reach the gelling point. Further the wood treatment method includes the steps of applying the water based formulation on the wooden material and drying the wooden material treated with said water based formulation at any given temperature in order to remove excess of water and also curing the dried wooden material at an elevated temperature in order to insolubilize the alkali metal silicate.