Surface retention of polyurethane and acrylic coatings on impregnated spruce wood (Picea abies Karst) and comparison with some wood preservatives

The natural spruce wood has low resistance against biological degradation and weather effects, so further protection is required, up to meeting the durability requirements for wood used in exterior classes. According to the wood preservatives standards, coatings as water repellents belong to the group OS (organic solvent) preservatives. The coatings have a water-repellent function, and they are not toxic, so these advantages make them usable like impregnation material.  The objective of this work is impregnation of the spruce wood (Picea abies Karst) using the “Double vacuum process” with coating material based on polyurethane and acrylic isocyanate resins and determinate the coatings quantity in wood. The impregnation efficiency is expressed through the retention. The coatings retention is compared with the minimal standard prescribed retention of the preservatives, most frequently used, namely creosote, copper chrome arsenate (CCA) and waterborne copper-rich systems like copper azole (CBA-A, Thanalite E), to show the efficiency of the applied double vacuum process. The coating retention is not significantly different from the minimum prescribed retention of creosote and amounts 118 - 149 kg/m3 or 32 to 38 times higher than the recommended retention of CCA or CBA-A for wood protection in the exterior use. The polyurethane and acrylic wood coatings can be successfully applied for wood impregnation purposes. Key words: impregnation, retention, spruce wood, polyurethane coatings, acrylic isocyanate coatings.