Wetting of elements of external decks was researched with regard to their construction. The main goal was to determine the quantity of absorbed water and in this way to assess the influence of wetting on wood dimension stability in regard to fixation. The test methods were the SIST EN 927-5 and the artificially accelerated aging. It turned out that the front side screwed together with siliconizing is an inefficient way of fixation. Due to in efficient silicon sealing and an increased portion of the front wood from the borehole, the volume of absorbed water increases. Backside screwing proved to be very efficient, since in this case, the volume of absorbed water was the smallest. Unfortunately, this way of fixation cannot always be carried out in real situations. Using the method of artificially accelerated aging, noticeable changes on the wooden deck were exhibited and analysed. The boards of the decks bent and changed dimensions as well as colour. However, it was not possible to find out the pros of individual fixation systems on the basis of final results of artificially accelerated aging. Furthermore, both methods were used to test and analyse the samples made of a wood-polymer composite. The material demonstrated good dimension stability and considerably lower water absorption compared to absorption of solid wood.