This research is mainly focused on the impact of thermal modification on the transverse anisotropy and dimensional stability of native beech wood (Fagus sylvatica L.) and beech red heartwood. Applied to two time-temperature regimes, the first period of maximum temperature to 180° C and the second to 230° C. The factor of anisotropy in native beech wood is 1.29 and beech red heartwood is 1:24. Dimensional stability of the native beech wood is improved for 33.3% and beech red heartwood for 29.1%. The changing of the volume mass per thermal modification of 6% is too small and does not affect other properties.

Impregnating materials may affect the stabilization of wood dimensions in two ways: blocking of free water movement paths and chemical connection with hydroxyl groups of wood. The degree of modifi cation depends on the applied material, its penetration and fi xation to the wood. The paper investigates the impact of impregnation and coating with polyurethane and acrylic coatings of spruce wood (Picea abies Karst.) on absorption of water and dimensional stability of wood (anti-shrinking effi ciency) after being immersed in water for a specifi c time. Impregnated spruce wood absorbs two times less water than untreated wood and it is dimensionally more stable than coated spruce wood. The water absorption of coated spruce wood is low, but it is not dimensionally stable.

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.