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Recycled recovered wood, for example, from historic buildings, containing biocides, fire retardants or anti-weather paints is an attractive material for manufacturing composite wood panels which can be used for decoration as well as load-bearing walls with a typical patina. This paper investigates the effect of four inorganic wood preservatives—CuSO₄·5H₂O, ZnCl₂, H₃BO₃ and (NH₄)₂SO₄—commonly used in the past, with the focus on their effect on the quality of wood bonding. The milled surfaces of Norway spruce (<i>Picea abies</i> Karst L.) wood were treated with 0.5, 1 and 2% aqueous solutions of these preservatives. The effect of preservatives in spruce wood was evaluated: (1) by its wettability with the drops of redistilled water, measuring the contact angles; (2) by the shear strength of the “spruce wood—polyurethane (PUR) Kestopur 1030 glue” interphases according to the standard EN 205; (3) by microscopic analysis of the “wood—PUR” interphases. The wettability of spruce wood worsened when using ZnCl₂, by a maximum of 28.2%, but on the contrary, it improved due to other preservatives mainly by using (NH₄)₂SO₄, at a maximum of 22.9%. In general, the shear strength of glued joints “wood—PUR” continually decreased with higher concentrations of all the preservatives. The most significant decrease of adhesion “wood—PUR”, by 19.8% from 10.66 MPa to 8.55 MPa, was caused by 2% ZnCl₂ used for the treatment of both spruce wood specimens in interphase with the PUR glue. On the contrary, the less significant decrease of adhesion “wood—PUR”, by 2.5%, was caused by 0.5% (NH₄)₂SO₄ applied only on one surface of the two inter-bonded spruce wood specimens. The effects of preservatives on the wood wettability and its adhesion with PUR glue were partly confirmed by microscopic analysis.